Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

We have performed surface acoustic wave (SAW) measurements to examine vacancies in a surface layer of a borondoped silicon wafer currently used in semiconductor industry. A SAW with a frequency of f(s) = 517MHz was optimally generated by an interdigital transducer with a comb gap of w = 2: 5 mu m on a piezoelectric ZnO film deposited on the (001) silicon surface. The SAW propagating along the [100] axis with a velocity of v(s) = 4: 967 km/s is in agreement with the Rayleigh wave, which shows an ellipsoidal trajectory motion in the displacement components u(x) and u(z) within a penetration depth of lambda(p) = 3.5 mu m. The elastic constant C-s of the SAW revealed the softening of Delta C-s/C-s = 1.9 x 10(-4) below 2K down to 23 mK. Applied magnetic fields of up to 2 T completely suppress the softening. The quadrupole susceptibilities based on the coupling between the electric quadrupoles O-u, O-v, and O-zx of the vacancy orbital consisting of 8-7 states and the symmetry strains epsilon(u), epsilon(v), and epsilon(zx) associated with the SAWaccount for the softening and its field dependence on C-s. We deduced a low vacancy concentration N = 3.1 x 10(12)/cm(3) in the surface layer within -lambda = 3.5 mu m of the silicon wafer. This result promises an innovative technology for vacancy evaluation in the fabrication of high-density semiconductor devices in industry.

DOI： 10.7566/JPSJ.83.034702

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

We study the ternary clathrate Pr3Pd20Si6 in specific heat and ac susceptibility measurements on a high-quality single crystal, distinguishing antiferromagnetic and antiferroquadrupolar ordering, as well as a hitherto unknown magnetic low-temperature transition. The specific heat shows the direct involvement of nuclear spin degrees of freedom in the antiferromagnetic ordering, which is well supported by our calculation of the hyperfine level scheme without adjustable parameters. Pr3Pd20Si6 is, therefore, one of the rare materials where the nuclear moments are involved in the formation of the magnetic ground state.

DOI： 10.1103/PhysRevLett.111.077202

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

We have investigated the quadrupole ordering of 4f-electrons and the rattling motion of guest rare-earth ions in the clathrate compound Pr3Pd20Ge6 using ultrasonic measurements. The elastic constants (C-11 - C-12)/2 and C-44 exhibit considerable softening at low temperatures. A minimum of (C-11 - C-12)/2 at T-Q1 = 0.25 K indicates antiferroquadrupole ordering associated with a Gamma(3) doublet of a crystal-field ground state at the 8c site, while a minimum of C-44 at T-Q2 = 60 mK indicates the ferroquadrupole ordering of a Gamma(5) triplet of a crystal-field ground state at the 4a site. The antiferroquadrupole phase depending on magnetic field direction shows a highly anisotropic behavior. The field-induced ordered phase due to the level crossing of the CEF ground state at the 8c site in magnetic fields along the [001] direction has been found. Furthermore, for the elastic constant C-44 and the attenuation coefficient alpha(44) we found a frequency dependence at two different temperatures of 15 and 25 K, which we describe in terms of the Debye-type dispersion with an Arrhenius-type relaxation time tau = tau(0) exp(E/k(B)T) for two different activation energies of E-L = 102 K and E-H = 198 K. These ultrasonic dispersions are caused by the thermally activated rattling motions of guest rare-earth Pr3+ ions at the 4a site of Pr3Pd20Ge6.

DOI： 10.1143/JPSJ.81.034710

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

The low-temperature ultrasonic dispersion in the transverse (C-11 - C-12)/2 mode of PrMg3 with the non-Kramers-doublet ground state has been investigated in temperatures down to 20 mK. The dispersion is caused by a thermally activated motions characterized by an Arrhenius-type relaxation time of tau = tau(0) exp(E/k(B)T) with low activation energy, E = 500 mK, and slow attempt time, tau(0) = 0 8.5 x 10(-10) s. The coupling of the electric quadrupoles of the non-Kramers-doublet ground state to transverse lattice vibrations leads to a vibronic ground state with dissipation. The vibronic state in PrMg3 releases the entropy of k(B) ln2 with lowering temperature across the activation energy. A Kondo-like singlet state due to the binding of the non-Kramers doublet to the lattice vibrations appears at low temperatures far below the activation energy.

DOI： 10.1143/JPSJ.81.023710

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We have investigated low-temperature properties at a longitudinal elastic constant C-L[111] of a boron-doped silicon crystal grown by a floating zone (FZ) method. The softening of C-L[111] depending on magnetic fields indicates that a magnetic charge state V+ of a vacancy orbital accommodating three electrons is stable. Appreciable anisotropy in the softening of C-L[111] at magnetic fields along the [111] and [1 (1) over bar0] axes up to 10 T is described in terms of a quadrupole susceptibility for the vacancy orbital consisting of a Gamma(8) quartet ground state and Gamma(6) doublet excited state due to the spin-orbit interaction.

DOI： 10.1143/JPSJ.80.094601

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

Elastic properties of cubic PrMg3 with a non-Kramers Gamma(3) doublet ground state have been investigated with ultrasonic measurements. The temperature dependence of the elastic constant (C-11-C-12)/2 in PrMg3 exhibits a characteristic minimum around 28 K and successively shows pronounced softening below 8 K down to 20 mK. The observation is well described by multipole susceptibility considering both an electric quadrupole O-v and electric hexadecapole H-v with Gamma(3g) representation for the crystal field level Gamma(3) ground state and Gamma(4) triplet excited state located at 54 K for PrMg3. The contribution of the hexadecapole in the Gamma(3)-Gamma(4) system to the multipole susceptibility should be emphasized to explain a common feature of the minimum typically observed in (C-11-C-12)/2 of Pr-based compounds PrPb3, PrAg2In, and the present PrMg3, as revealed by systematic ultrasonic measurements.

DOI： 10.1103/PhysRevB.84.045110

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

We have performed ultrasonic experiments on clathrate compounds ROs4Sb12 and R3Pd20Ge6 to explore rattling and tunneling of a guest rattler's motion. We have found frequency dependence of the elastic constants and ultrasonic attenuations, which is called as ultrasonic dispersion, due to thermally activated rattling. At low temperatures, Curie-type elastic softening obeying 1/T with antiferro-type intersite interaction, which corresponds to quantum tunneling, appears and continues even to the lowest 20 mK in LaOs4Sb12 and La3Pd20Ge6. The understanding of the local charge fluctuation, rattling and tunneling, being coupled to conduction electrons in metals is a basic issue in the aspect of electron-phonon interaction in strongly correlated phenomena such as heavy fermion state, superconductivity and multi-channel Kondo screening effect.

DOI： 10.1143/JPSJS.77SA.153

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Ultrasonic attenuation measurements have been firstly performed for a large single crystal of PrOs4Sb12 with the dimensions of 5.97 x 0.6 x 0.6 mm(3). Remarkable frequency dependence around 20-40K has been observed in the elastic constant and attenuation coefficient of the longitudinal C-11 mode associated with E-g symmetry strain in part, which results from a thermally activated off-center rattling with E-g symmetry of a Pr ion inside a Sb icosahedron cage. Parameters of a characteristic time tau(0) = 3.1 x 10(-11) s and an activation energy E = 225 K were obtained. This E-g rattling involving a local charge fluctuation inside a Sb cage periodically arranged may couple to the conduction electrons. As a result, the electron-phonon coupling would lead to heavy fermion and its superconductivity in PrOs4Sb12. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2006.01.070

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

We present tunneling and rattling motions of an off-center guest atom in a cage referring to a clathrate crystal La3Pd20Ge6. The elastic constant C-44 of La3Pd20Ge6 shows a Debye-type dispersion of around 20 K obeying a relaxation time tau=tau(0) exp(E/k(B)T) with an attempt time of tau(0)=2.0x10(-12) s and an activation energy E=197 K. At low temperatures below 3 K down to 20 mK, the C-44 shows a softening of C-44=C-44(0)(T-T-C(0))/(T-Theta) with T-C(0)=-337.970 mK and Theta=-338.044 mK. These facts are attributed to two different types of off-center motions with Gamma(5) symmetry in the 4a-site cage of La3Pd20Ge6, a thermally activated rattling motion over the potential hill, and a tunneling motion through the potential hill at low temperatures.

DOI： 10.1103/PhysRevB.70.184126

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

The elastic properties of a filled skutterudite PrOs4Sb12 with a heavy fermion superconductivity at T-C=1.85 K have been investigated. The elastic softening of (C-11-C-12)/2 and C-44 with lowering temperature down to T-C indicates that the quadrupolar fluctuation due to the CEF state plays a role for the Cooper paring in superconducting phase of PrOs4Sb12. A Debye-type dispersion in the elastic constants around 30 K revealed a thermally activated Gamma(23) rattling due to the off-center Pr-atom motion obeying tau=tau(0) exp(E/k(B)T) with an attempt time tau(0)=8.8x10(-11) s and an activation energy E=168 K. It is remarkable that the charge fluctuation of the off-center motion with Gamma(23) symmetry may mix with the quadrupolar fluctuation and enhance the elastic softening of (C-11-C-12)/2 just above T-C.

DOI： 10.1103/PhysRevB.69.180511

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

Lattice effects in a cerium based clathrate compound Ce3Pd20Ge6 with a cubic Cr23C6-type structure have been investigated by ultrasonic and thermal expansion measurements. Elastic softenings of (C-11-C-12)/2 and C-44 proportional to the reciprocal temperature 1/T above T-Q1=1.25 K are well described in terms of the quadrupole susceptibility for the ground state Gamma(8) quartet. A huge softening of 50% in (C-11-C-12)/2 and a spontaneous expansion DeltaL/L=1.9x10(-4) along the [001] direction in particular indicate the ferroquadrupole ordering of O-2(0) below T-Q1. The elastic anomalies associated with the antiferromagnetic ordering at T-N2=0.75 K and the incommensurate antiferromagnetic ordering are also found. Notable frequency dependence of C-44 around 10 K is accounted for by the Debye-type dispersion indicating a Gamma(5) rattling motion of an off-center Ce ion along the [111] direction with eight fractionally occupied positions around the 4a site in a cage. The thermally activated Gamma(5) rattling motion obeying a relaxation time tau=tau(0) exp (E/k(B)T) with an attempt time tau(0)=3.1x10(-11) sec and an activation energy E=70 K dies out with decreasing temperature, and then the off-center tunneling state of Ce ion in the 4a-site cage will appear at low temperatures.

DOI： 10.1103/PhysRevB.68.184109

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We have performed low-temperature ultrasonic investigations using a top-loading type dilution refrigerator to examine the detailed H-T phase diagrams below 1 K in Ce3Pd20Ge6. The field dependence of the elastic constant C44 under fields along [0011 and (CH Ci(2))/(2) under fields along [1101 shows the anomaly which is the phase transition point from autiferromagnetic (AFI\4) phase III coexisting ferroquadrupolar (FQ) ordering to pure FQ phase II. Several anomalies corresponding to subphases near 0,5 T. 1,2 T and i.6 T have been observed in both cases, These anomalies are closely related to the weak incommensurate magnetic Bragg peaks below 0.5 K with a propagation vector k [0,0,1-tau] (tau similar to 0.06), observed by the neutron diffraction for Ce3Pd20Ge6. In the series of R3Pd20 compounds, two successive AFM phase transition at Tivi characterized by a propagation vector k(1)=[111] at Sc sites and T-N2 characterized by k(2)=10011 at 4a sites were commonly observed. In Ce3Pd20Ge6, a structural phase transition associated with the (O-2(0-) (or O-2(2-)) type FQ ordering at Sc sites will prevent the AFM ordering at Sc sites preferable along k(1)=.11111.

DOI： 10.1143/JPSJS.71S.121

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

Elastic properties of the perovskite manganite La1-xSrxMnO3 (x=0.12, 0.165, 0.3) with both orbital and charge degrees of freedom have been investigated by means of ultrasonic measurements. Above the structural phase transition point T-s = 290 K for x = 0.12 and T-s= 310 K for x = 0.165, the transverse (C-11- C-12)/2 mode with the elastic strain of E-g symmetry exhibits a pronounced softening, while the C-44 mode with strain of T-2g symmetry shows a monotonous increase in lowering temperature. The softening of (C-11- C-12)/2 is described in terms of the quadrupolar susceptibility for the coupling between the quadrupolar moment, O-2(0)=(2l(z)(2)-l(x)(2) -l(y)(2))/ root3 and O-2(2)=l(2)(2)-l(y)(2), of the dy doublet of the Mn3+ ion and appropriate elastic strain with E-g symmetry. Elastic softenings of (C-11- C-12)/2 and C-44 modes above T-co = 145 K of x= 0.12 are responsible for the symmetry breaking character of the charge ordering, while a round minimum of the bulk modulus CB around T-co = 100 K of x = 0.165 indicates a glass state in charge ordering. The disappearance of the ultrasonic echo signal below T-co=145 K for x=0.12 is ascribed to a considerable sound wave scattering by elastic domains in the triclinic structure.

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The elastic constant of C-44 in Yb4As3 relating to the transverse ultrasonic mode shows a pronounced softening around the structural phase transition point at T-c = 292 K associated with the charge ordering of Yb3+ and Yb2+ states. The group theoretical analysis leads to the charge fluctuation mode with Gamma(5) symmetry coupled to the elastic strain epsilon(yz), epsilon(zx), epsilon(xy) of the soft C-44 mode. In a framework of the Landau phenomenological theory for the phase transition, the order parameter Q(yz) = Q(zx) = Q(xy) not equal 0 below T-c gives rise to the linear chain of Yb3+ ions among the body diagonal [111] direction as well as the trigonal distortion of epsilon(yz) = epsilon(zx) = epsilon(xy) not equal 0. Furthermore, this theory explains experimental observations of the elastic softening C-44 = C-44(0)(T-T-c(0))/(T-Theta) above T-c, the structural change from cubic phase of T-d(6) to trigonal phase of C-3 upsilon(6), and the first-order nature of the transition. [S0163-1829(99)00301-X].

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The magnon excitation by ultrasound injection in Y$_3$Fe$_5$O$_{12}$ is studied by inelastic neutron scattering. Both longitudinal and transverse ultrasound injections enhanced the inelastic neutron scattering intensity.

DOI： 10.1063/5.0189768

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DOI： 10.7566/JPSJ.92.124710

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society (APS)  

Ultralow-lying magnon energy spectrum in yttrium iron garnet (YIG) has been studied by inelastic neutron scattering in an energy range from 10 to 45 mu eV. When a magnetic field of approximately 0.1 T was applied along [111] direction, ultralow-energy magnon anomaly was found at 10 K, suggesting the closure of the Zeeman energy gap. The anomaly was also observed in the temperature dependence of magnetization under a magnetic field along the [111] direction below 30 K. The specific heat capacity confirms the closure of the Zeeman energy gap at the magnetic field direction. All these anomalies strongly support the magnetic crossover below 30 K under the magnetic field along [111], in addition to a precursor anomaly below 150 K.

DOI： 10.1103/physrevresearch.2.033235

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Other Link： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevResearch.2.033235/fulltext

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Physics Publishing  

In Pr3Pd20Ge6, the Pr ions are located at two different crystallographic sites, 4a and 8c site. Antiferro-quadrupole ordering (AFQ) of the 8c site occurs at 250 mK. Ac susceptibility measurement indicated that antiferromagnetic ordering (AFM) of the 4a site and Hyperfine-enhanced Pr nuclear magnetic ordering of the 8c site occur at 77 and 9 mK, respectively. To clarify the magnetic and quadrupole properties of Pr3Pd20Ge6, thermal expansion and magnetostriction measurements on single crystal sample were carried out along the [001] direction up to 8 T down to 500 μK using a capacitive dilatometer. In zero field, relative length change ΔL/L in [001] direction had a dip at AFQ and abrupt decrease at AFM ordering. From thermal expansion and isothermal magnetostriction measurements, magnetic phase diagram of Pr3Pd20Ge6 along [001] direction was obtained.

DOI： 10.1088/1742-6596/969/1/012120

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society  

The nuclear and magnetic structure and full magnon dispersions of yttrium iron garnet Y3Fe5O12 have been studied using neutron scattering. The refined nuclear structure is distorted to a trigonal space group of R3̄. The highest-energy dispersion extends up to 86 meV. The observed dispersions are reproduced by a simple model with three nearest-neighbor-exchange integrals between 16a (octahedral) and 24d (tetrahedral) sites, Jaa, Jad, and Jdd, which are estimated to be 0.00±0.05, -2.90±0.07, and -0.35±0.08 meV, respectively. The lowest-energy dispersion below 14 meV exhibits a quadratic dispersion as expected from ferromagnetic magnons. The imaginary part of q-integrated dynamical spin susceptibility χ″(E) exhibits a square-root energy dependence at low energies. The magnon density of state is estimated from χ″(E) obtained on an absolute scale. The value is consistent with the single chirality mode for the magnon branch expected theoretically.

DOI： 10.1103/PhysRevB.97.054429

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

Complex ac susceptibility, chi = chi' - i chi '', measurements of the clathrate compound Pr3Pd20Ge6 were performed in static fields up to 10 mT for H parallel to [001] and at temperatures down to 500 mu K. Praseodymium (Pr) nuclear magnetic moments at the 8c site, where quadrupole moments of 4f electrons order at T-Q1 = 250 mK, were found to order antiferromagnetically at 9 mK, as shown by a peak in chi' and a substantial increase in thermal relaxation time. The large enhancement factor (1 + K-8c) obtained by calculation of the hyperfine-enhanced nuclear susceptibility of Pr at the 8c site accounts for the high transition temperature of Pr nuclear magnetic moments and the large chi' below 30 mK. From analysis of the crystalline electric field and the mean-field approximation, we conclude that a chi peak at 77 mK can be ascribed to an antiferromagnetic ordering of magnetic moments of 4f electrons at the 4a site. We found that nuclear and f-electron moments order separately on two sublattices in this compound. The temperature and magnetic field dependence of chi' and chi '' between 30 and 60 mK are discussed in terms of dissipation phenomena.

DOI： 10.1103/PhysRevB.90.100402

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Electrochemical Society Inc.  

For the samples taken from the void region of the CZ silicon crystal grown with the same solidification condition and different thermal histories after the solidification, we measure the magnitude S of the elastic softening which is proportional to the concentration of the single vacancies [V], For these samples, we also measure the size distribution of the void density by using the infrared lightscattering tomography, to evaluate the concentration [Vc] of the vacancies consumed for the void formation. From these two experiments, we find a sum rale [Vc] + a S= C, where C depends only on the solidification condition and is independent of the thermal history after the solidification. This enables us to find the conservation rale of the vacancies [Vc] + [V] = C. The value of the proportionality constant a in the relation [V] = a S is determined. Demonstration of determining the absolute values of [V] from the measured S is given. An estimate is made for the value of the quadrupole-strain coupling constant.

DOI： 10.1149/06411.0013ecst

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

We have carried out ultrasonic measurements of a boron-doped silicon ingot grown by the Czochralski method in order to determine the quadrupole-strain interaction constant of a vacancy orbital. The low-temperature softening of the elastic constant C-44 shows a remarkable variation depending on positions of the ingot, which reflects the distribution of vacancy concentration N in the ingot. An infrared laser scattering tomograph was employed to measure the density and size of voids in the silicon wafers by determining the vacancy concentration N-cons consumed in void formation. Using a combination of laser scattering tomography and low-temperature softening, we have found a sum rule in which the initially created vacancy concentration N-total corresponds to the sum of the residual vacancy concentration N and the consumed vacancy concentration N-cons as N-total N + N-cons. Taking account of the sum rule, we deduce the interaction constant g(Gamma 5) = (2.8 +/- 0.2) x 10(5) K for the quadrupole-strain interaction H-QS = -g(Gamma 5)O(zx)epsilon(zx) of the vacancy orbital. The huge deformation energy of 1.6 x 10(5) K per vacancy with the Gamma(8) ground state for unit strain epsilon(zx) = 1 verified the strong electron-lattice interaction of the vacancy orbital. Employing the one-to-one correspondence between the softening of Delta C-44/C-44 = 1.0 x 10(-4) down to 30 mK and the vacancy concentration of N = 1.5 x 10(13) cm(-3), we can determine the vacancy concentration by low-temperature ultrasonic measurements. The present work surely puts forward a novel semiconductor technology based on low-temperature ultrasonic measurements for evaluating vacancy concentration in silicon wafers.

DOI： 10.7566/JPSJ.82.124604

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We have carried out low-temperature ultrasonic measurements using shear-mode ultrasound to clarify the quantum state of a vacancy orbital in boron-doped silicon grown by the floating zone (FZ) method. The elastic constants (C11-C12)=2 and C44 of the transverse mode exhibit considerable softening below 2 and 5K down to the base temperature of 30 mK, respectively. The elastic constant C44 measured by the three ultrasonic modes (kx
uy), (kz
ux), and (kx
uz) shows the different magnetic field dependences among the configurations under applied magnetic fields along the z-axis. The elastic softening and the magnetic field dependence of the elastic constants are accounted for by the quadrupole susceptibility based on the energy level scheme of the vacancy orbital with a λ8 quartet ground state and λ7 doublet excited state located at an energy of 1K. The difference in C44 between the two ultrasonic modes (kz
ux) and (kx
uz) at fields along the z-axis indicates that the λ8 quartet ground state is slightly split by local strain in the silicon sample. The quantum state of the vacancy orbital is expected to be sensitive to strain because of the extremely large quadrupole-strain coupling energy of gλ ≈ 105 K due to the extensively spreading orbital radius of r ≈ 1 nm. The differences in variation of the low-temperature softening and magnetic field dependence among eight samples cut out from different locations of the present boron-doped FZ silicon ingot evidence the inhomogeneous distribution of the vacancy concentration. © 2013 The Physical Society of Japan.

DOI： 10.7566/JPSJ.82.084604

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We have investigated quadrupole effects in tetragonal crystals of PrCu2Si2 and DyCu2Si2 by means of low-temperature ultrasonic measurements. The elastic constant C-44 of PrCu2Si2 exhibits pronounced softening below 70 K down to a Neel temperature T-N = 20 K, which is described in terms of a quadrupole susceptibility for a Gamma(5) doublet ground state and a Gamma(3) singlet first excited state located at 15.6 K in the crystalline electric field scheme. The C-44 and C-66 of DyCu2Si2 also show softening below 70 K down to T-N1 = 9.7 K. A low-lying pseudo-sextet state consisting of three Kramers doublets of Gamma(6) circle plus 2 Gamma(7) brings about softening of C-44 and C-66 in DyCu2Si2.

DOI： 10.1088/0953-8984/25/29/296002

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

To investigate the origin of a phase transition at T-Q = 0.06 K simultaneously occurring with a superconducting transition in a cage compound PrRh2Zn20, we carried out ultrasonic measurements on a single-crystalline sample. The transverse modulus (C-11 - C-12)/2 is intimately coupled to the non-Kramers ground doublet Gamma(3), and elastic softening is observed at low temperatures. Below T-Q, the softening stops, suggesting the disappearance of quadrupole degrees of freedom. We clarified the negative quadrupole-quadrupole coupling constant and reentrant behavior of T-Q(H) in a magnetic field H. These results reveal that the phase transition at T-Q is antiferroquadrupolar ordering. The anisotropic magnetic field-temperature phase diagram is determined for H parallel to [100], [110], and [111]. A magnetic-field-induced phase transition is newly found at high fields in all three field directions. We also observed ultrasonic dispersion at around 50 K owing to the rattling motion of Zn atoms at the 16c site, and pointed out the strong electron-phonon coupling in PrRh2Zn20.

DOI： 10.1103/PhysRevB.87.205106

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The tetragonal compound TbCoGa5 exhibits two successive magnetic transitions at T-N1 = 36.2 and T-N2 = 5.4 K. The results of the measurement of the magnetic susceptibility and specific heat indicate that the c- and ab-components of the magnetic moments of Tb3+ show independent antiferromagnetic orderings at T-N1 and T-N2, respectively. In this work, we have investigated the physical properties of TbCoGa5 in a magnetic field. Single crystals of TbCoGa5 were grown and their specific heat, electrical resistivity, magnetization and elastic constant were measured. The magnetic exchange interactions in TbCoGa5 are discussed referring to the result of the magnetization process. Additionally, the present and previous results are summarized in a magnetic phase diagram. The magnetic phase diagram indicates that the behavior of T-N1 in a changing magnetic field is similar to that of an Ising spin system, and the behavior of T-N2 is similar to that of an XY spin system. Thus, we conclude that Ising and XY spin systems coexist on a single Tb atom in TbCoGa5.

DOI： 10.7566/JPSJ.82.044713

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We present results of specific heat measurements on a Ce3Pd20Si6 single crystal and construct the magnetic phase diagram for the three cubic principal directions [100], [110] and [111]. The highly anisotropic phase diagram is discussed and can be qualitatively explained by the Zeeman splitting at the 8c-site. For B parallel to [100], the present study found two different quadrupolar ordered phases, which meet the paramagnetic phase at a tri-critical point and establish the new phase boundaries.

DOI： 10.1088/0953-8984/25/12/126003

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：TRANS TECH PUBLICATIONS LTD  

For the boron-doped FZ silicon crystals grown with and without nitrogen-doping (N-doping), we measured the temperature dependence of the elastic constant in low-temperature region, to examine whether the N-doping suppresses the elastic softening due to the gap-states of the isolated single vacancy. We have found that the elastic softening observed for the N-doping-free crystals is not observed for the N-doped ones, suggesting that the gap-states of the vacancies causing the elastic softening are destroyed by the N-doping. This is consistent with the model of Abe [T. Abe, J. Crystal Growth, 327 (2011) 1] in which the nitrogen molecule (N2) occupies the vacancy to destroy its original gap-states. We have further observed that the N-doped silicon, which shows no softening in its as-grown state, exhibits the softening after the annealing at 1000 degrees C for 1 min. This suggests that during the annealing the N2 molecule is thermally activated to jump off the lattice site leaving the vacancy.

DOI： 10.4028/www.scientific.net/MSF.725.217

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We report the specific heat measurement of single crystalline Ce3Pd20Si6 and the resultant magnetic phase diagram for the direction of B//[100]. In zero field, we confirmed two successive phase transitions at T = 0.24 K and 0.4 K. The magnetic phase diagram clearly shows a phase boundary of paramagnetic phase I, quadrupole ordered phase II and II'.

DOI： 10.1088/1742-6596/391/1/012054

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The cage compound PrIr2Zn20 with the non-Kramers doublet ground state shows a phase transition at T-Q similar to 0.11 K. To investigate the origin of the phase transition, we have carried out ultrasonic measurements on single-crystalline samples. From the disappearance of electric quadrupole degrees of freedom at T-Q and the negative sign of a quadrupole-quadrupole coupling constant, we clarified that the phase transition is antiferro-quadrupolar ordering at the lowest temperature ever measured. We also found anisotropic magnetic field H dependence and the re-entrant behavior of T-Q(H) from the measurements in H parallel to the [100], [110], and [111] axes. The quadrupole Kondo effect interrupts the long-range quadrupole interaction at very low temperatures and thus lowers T-Q. We first reported the rattling motion of Zn atoms at the 16c site in the RT2Zn20 system.

DOI： 10.1143/JPSJ.80.093601

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Elastic constant measurements on iron pnictide Ba(Fe0.9Co0.1)(2)As-2 with an optimal superconducting transition temperature of T-SC = 23 K have been performed by the ultrasonic pulse echo method. The shear elastic constant of C-66 associated with elastic strain epsilon(xy) reveals considerable softening of 21% below 300 K down to T-SC and becomes increasing in the superconducting phase below T-SC, while other shear elastic constants of (C-11 -C-12)/2 and C-44 show no sign of softening below 80 K down to 4.2 K. The electric quadrupole O-v' existing in the degenerate d(y'z) and d(zx') bands participates in the superconductivity of the present iron pnictide system.

DOI： 10.1143/JPSJ.80.073702

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Ultrasonic measurements of U3Pd20Si6 were performed in order to investigate elastic properties of the cage-structured compound U3Pd20Si6 and also examine a presence of ultrasonic dispersion (UD) due to off-center rattling, which has been observed in the elastic constant C-44 of similar systems R3Pd20Ge6 (R = La - Nd). At temperatures over antiferromagnetic ordering at T-N = 19 K, neither an up-turn anomaly nor frequency dependence of the elastic constants, regarding the UD, was found. On the other hand, the elastic constant C-44 shows pronounced softening due to crystalline electric field effect of U4+ ion's Gamma(5) triplet ground state for both 4a and 8c sites. Below T-N, precipitous elastic softening accompanied by a sudden depression of ultrasonic echo was observed in each ultrasonic mode. A drastic change of Delta C-44/C-44 similar to 30% at T-N, in particular, implies a strong magneto-elastic coupling of 5f-electrons or a possible contribution of a ferroquadrupole interaction to the antiferromagnetism in U3Pd20Si6.

DOI： 10.1143/JPSJS.80SA.SA105

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The elastic properties of TbCoGa5 single crystal were investigated by the measurement of the elastic constants under magnetic fields. The results of the measurement are consistent with successive component-separated magnetic orderings in TbCoGa5. The elastic properties in high magnetic fields indicate that the spin system is strongly affected by the quadrupole moment system in TbCoGa5. Such a mutual influence assumes an important role in the occurrence of the successive component-separated magnetic transitions.

DOI： 10.1143/JPSJS.80SA.SA082

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Inelastic neutron scattering has been employed to determine the complete crystal field (CF) level diagrams at the Pr sites (8c) and (4a) in the clathrate compound Pr3Pd20Si6 with cubic Cr23C6-type crystal structure. The splitting of the H-3(4) multiplet of Pr3+ was found to be Gamma(3) -> Gamma(5) (1.44 meV) -> Gamma(4) (4.46 meV) -> Gamma(1) (10.7 meV) at the (8c) site and Gamma(5) -> Gamma(3) (0.70 meV) -> Gamma(4) (10.8 meV) -> Gamma(1) (24.8 meV) at the (4a) site. We present additional measurements of the specific heat down to 2K and single-crystal high-field magnetization up to 28 T, and show that a calculation with no adjustable parameter based on our CF parameters can quantitatively reproduce the magnetic part of the specific heat and the magnetization curves along three cubic high-symmetry directions. We extrapolate the CF parameters obtained for Pr3Pd20Si6 to those of the isostructural compounds Ce3Pd20Si6, Nd3Pd20Si6 and Er3Pd20Si6, and compare the results with inelastic neutron scattering experiments reported in literature. For the (8c) site, the experimentally determined CF level diagrams are consistent and in good agreement with the extrapolation. In contrast, for the (4a) site, the few available experimental results are inconsistent and in poor agreement with the extrapolation. The extrapolation says that in Ce3Pd20Si6 the CF ground-state at both Ce sites (8c) and (4a) is the Gamma(8) quartet.

DOI： 10.1143/JPSJ.80.044715

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Elastic properties of the filled skutterudite compound SmOs4Sb12 have been investigated by ultrasonic measurements. The elastic constant C-11(omega) shows two ultrasonic dispersions at similar to 15 and similar to 53K for frequencies omega between 33 and 316 MHz, which follow a Debye-type formula with Arrhenius-type temperature-dependent relaxation times and remain unchanged even with applied magnetic fields up to 10 T. The corresponding activation energies were estimated to be E-2 = 105K and E-1 = 409 K, respectively. The latter, E-1, is the highest value reported thus far in the Sb-based filled skutterudites. The presence of magnetically robust ultrasonic dispersions in SmOs4Sb12 implies a possibility that an emergence of a magnetically insensitive heavy fermion state in this system is associated with a novel local charge degree of freedom, which causes the ultrasonic dispersion.

DOI： 10.1143/JPSJ.80.043601

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We have studied quadrupole ordering and rattling in clathrate compound Pr3Pd20Ge6 using ultrasonic measurements. The softening were observed in temperature dependence of elastic constants C-11, (C-11 - C-12)/2 and C-44. The C-11 and (C-11 - C-12)/2 show minimums at 250 mK indicating a transition point to an antiferroquadrupole ordered phase due to a F3 doublet ground state at 8c site. Furthermore, the C-11, (C-11 - C-12)/2 and C-44 exhibit discontinuitive anomalies at 60 mK revealing a ferroquadrupole ordering due to a F-5 triplet ground state at 4a site. Two distinctive ultrasonic dispersions caused by thermally activated F-5-type rattling were observed in C-44 around 15 K and 25 K.

DOI： 10.1088/1742-6596/273/1/012002

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We have investigated low-temperature elastic properties of PrMg(3) with a non-Kramers Gamma(3) doublet ground state by using ultrasonic measurements under high field up to 18 T down to 20 mK. A softening of the elastic constant (C(11)-C(12))/2 has been observed below 8 K due to the non-magnetic Gamma(3) doublet possessing electric quadrupole O(u) and O(v) with Gamma(3) symmetry and magnetic octupole T(xyz) with Gamma(2). This result appreciably is deviated from a theoretical fitting of the quadrupole susceptibility based on the crystal-electric-field levels below 800 mK. Furthermore, the (C(11)-C(12))/2 shows strange magnetic dependence up to 18 T below 1.7 K, which are inconsistent with the theoretical results.

DOI： 10.1088/1742-6596/273/1/012133

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We succeeded in synthesizing a new cubic intermetallic compound PrCu4Ag in a fcc structure. Measurements of X-ray diffraction, magnetic susceptibility, magnetization, specific heat, electrical resistivity, thermal expansion, and elastic constants have been performed on single crystals of PrCu4Ag. A maximum value of chi(T) with a corresponding peak in C(T) suggests that an antiferromagnetic phase transition occurs at T-N = 2.4 K, where a sudden decrease in rho(4f)(T) and a sharp peak in the thermal expansion coefficient alpha(T) were observed. Characteristic Curie-type softening was observed in the temperature dependence of the transverse mode for (C-11 - C-12)/2 and C-44 from 70 K down to T-N, which implies that the crystalline electric field (CEF) ground state is the magnetic triplet Gamma(5). The anisotropic properties in M(T, H) and C(T, H) are studied when the external magnetic field is applied in the < 100 >, < 110 >, and < 111 > directions. Another anomaly observed at approximately 10 K in chi(T) is considered to be related to possible disorder behavior. The low-T behavior and the possibility of quadrupole fluctuation are discussed with respect to the CEF effect. All the experimental results in the present study are summarized in a magnetic phase diagram.

DOI： 10.1143/JPSJ.79.114707

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Magnetization of a single crystalline Ce3Pd20Si6 was measured at low temperatures down to 90 mK in fields up to 11 T for the three principal directions [100], [110], and [111]. For all directions, two transitions were observed in the temperature variation of the magnetization M(T) at 0.2 T; a broad peak at 0.28 K associated with a phase-III transition, and an upward bending at similar to 0.5 K due to a phase-II ordering from the paramagnetic state (phase-I). The latter critical temperature TI-II is found to be strongly enhanced in magnetic fields B, depending on the field direction, and TI-II(B) becomes highly anisotropic. These results suggest that phase-II is an antiferroquadrupole state originated from a Gamma(8) ground state. By contrast, no appreciable anisotropy is found in the phase-III state. At 90 mK, phase-III collapses by applying a field of similar to 0.63 T for all directions. Above this field, the magnetization curve M(B) becomes strongly anisotropic. The magnetization value per Ce in the phase-I region at 90 mK is apparently smaller than the Gamma(8) moment, indicating that either 8c or 4a site has a Gamma(7) ground state.

DOI： 10.1143/JPSJ.79.074712

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We have performed magnetization measurements of a single crystalline Ce3Pd20Si6 down to 90 mK in fields up to 11 T. Two transitions were recognized in M(T) at low fields; a cusp at 0.27 K due to a magnetic transition, and an upward bending at similar to 0.5 K that probably corresponds to a quadrupole transition. The latter critical temperature is found to be strongly enhanced in magnetic fields. The magnetization M(H) at 90 mK is strongly anisotropic above 0.6 T, and shows several sharp features associated with phase transitions. Interestingly, no appreciable anisotropy is found in the magnetic phase below 0.27 K and 0.6 T.

DOI： 10.1088/1742-6596/200/1/012118

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The paper reports the recent progress of our research on the vacancies in boron-doped (B-doped) as-grown silicon crystals of commercial-base quality achieved by means of the low-temperature ultrasonic measurements. The paper also demonstrates how our research-base technique for the vacancy observation is established as the practical tool of evaluating the vacancy concentration of the commercial silicon crystals and wafers. An emphasis is made on the confirmation of the following findings obtained in our previous experiment for the elastic softening by the vacancies in boron-doped silicon crystals: (1) the steep softening that suddenly starts at 2-4 K in the cooling process, and (2) the complete disappearance of the softening by a weak magnetic field of 4 T applied along [111] direction. We further investigate in detail how the low-temperature softening at a fixed temperature responds to the applied magnetic field, to find the following characteristic anisotropy: The manner of disappearance of the softening strongly depends on the direction of the magnetic field. For the magnetic field imposed along [1-10] direction, nearly 60% of the full softening still remains even at a strong magnetic field of 8 T, in contrast to the case of the magnetic field applied along [111] direction. ©The Electrochemical Society.

DOI： 10.1149/1.3485683

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In order to investigate ordered phases revealed at low temperatures in clathrate compound Pr3Pd20Si6, we have performed ultrasonic measurements using a single crystal in magnetic fields at low temperatures. Temperature dependence of elastic constant C-11 and C-L[1 (1) over bar0] = (C-11 + C-12 + C-2(44))/2 shows the anomalies at about 150 mK in zero field. Magnetic phase diagrams are determined by measuring C-11 in H parallel to [001] and C-L[1 (1) over bar0] in H parallel to [111]. The magnetic phase diagrams along the three principal axes indicate a closed loop and a strong magnetic anisotropy. This result suggests that antiferroquadrupole ordering appears at low temperatures in Pr3Pd20Si6.

DOI： 10.1088/1742-6596/200/1/012121

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We performed ultrasonic measurements on a single crystal of PrMg3. The characteristic Curie-type softening was observed in temperature dependence of transverse mode (C-11 - C-12)/2 below 8 K down to 0.8 K. This softening in PrMg3 is caused by a non-Kramers Gamma(3) doublet ground state having electric quadrupoles O-u and O-v and magnetic octupole T-xyz. The elastic constant (C-11 - C-12)/2 shows a minimum at 25 K, which cannot be explained by the quadrupole susceptibility based on the crystal electric field (CEF) levels. However, considering higher order (l = 4) multipole, namely electric hexadecapole, the minimum around 25 K was well reproduced. At lower temperatures, a shoulder anomaly in elastic constant being deviated from the Curie-type softening was observed around 100-800 mK in (C-11 - C-12)/2. This anomaly is unaffected by magnetic fields up to 14T. (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2009.07.051

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Ultrasonic measurements on a Pr0.55Nd0.45Os4Sb12 single crystal for temperature down to 20mK and frequencies up to 245 MHz were performed in order to investigate off-center rattling motion of rare-earth ions. The elastic constant C-11 exhibits double ultrasonic dispersions at similar to 15 and similar to 40 K, which are similar to the features found in NdOs4Sb12. The estimated activation energy E-1 = 240 K corresponding to the 40 K-dispersion, possesses an intermediate value between PrOs4Sb12 (E-1 = 115 K) and NdOs4Sb12 (E-1 = 337 K). (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2009.07.081

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Low-temperature elastic properties of the clathrate compound Ce3Pd20Si6 were investigated using ultrasonic measurements. Pronounced softening of elastic constants (C-11 - C-12)/2 and C-44 with decreasing temperature indicates a precursor of electric quadrupole ordering due to it Gamma(8) quartet ground sate with an orbital degeneracy for 8c site of it Ce ion. A minimum of (C-11 - C-12)/2 at T-C = 170 mK indicates a transition from paramagnetic phase I to an ordered phase III. Applied magnetic fields induce an antiferro-quadrupole (AFQ) ordered phase II with highly anisotropic character depending on the field direction, which resembles the AFQ phase with O-xy-type order parameter in CeB6 with the Gamma(8) ground sate. The order parameter of the phase III may be characterized by either magnetic dipole or magnetic octupole. The Gamma(7) ground state at 4a site may fall into it singlet screened by conduction electrons at low temperatures Without long-range magnetic ordering.

DOI： 10.1143/JPSJ.78.024716

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Using a low temperature x-ray diffractometer, we studied superconductivity materials, optimally doped and underdoped YBCOs and PrOs(4)Sb(12) between 0.1 K and 300 K. At several temperatures, whole profiles of the x-ray reflection peak were measured and refined by Rietveld analysis. By Rietveld analysis, we found that Pr atoms in PrOs(4)Sb(12) are still oscillating at an amplitude of about 0.1 angstrom at 0.18 K. For some reflection planes, x-ray diffraction measurement with a small step size and a long stepping time was performed to accumulate more counts at certain temperatures. The lattice constant d of optimally doped YBCO (OPT YBCO) shows anomalous behaviours at around the superconductivity transition temperature Tc and around spin gap temperature T*. In OPT YBCO, the intensity of the reflection spectrum shows a clear anomaly at around Tc.

DOI： 10.1088/1742-6596/150/5/052284

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Trans Tech Publications Ltd  

We confirm the following findings obt ained in our previous e xperiment for the low-temperature e lastic softening by the vacancies in boron-doped silicon crystals: (1) the steep softening that suddenly starts at 2-4 K in the cooling process, and (2) the complete disappearance of the softening by a weak magnetic field of 4 T applied along [111] direction. We further investigate in detail how the low-temperature softening at a fixed temperature responds to the applied magnetic field, to find the following characteristic anisotropy: The manner of disappearance of the softening strongly depends on the direction of the magnetic field. For the magnetic field imposed along [1-10] direction, nearly 60 % of the full softening still remains even at a strong magnetic field of 8 T, in contrast to the case of magnetic field applied along [111] direction. © (2010) Trans Tech Publications.

DOI： 10.4028/www.scientific.net/SSP.156-158.135

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The rattling motion in Ce-based filled skutterudite CeFe4Sb12 has been investigated by means of ultrasonic measurements. We found ultrasonic dispersion obviously in elastic constant C-44 between 35 and 70 K, suggesting the rattling motion of Ce atoms, and obtained a relaxation time tau(0) = 1.5 x 10(-12) s and an excitation energy E = 345 K of the rattling motion. tau(0), E and the temperature range of ultrasonic dispersion in CeFe4Sb12 are a little lower than that in LaFe4Sb12 and PrFe4Sb12. Elastic softening in C-44 is not observed down to 4.2 K.

DOI： 10.1088/1742-6596/150/4/042071

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We have performed ultrasonic measurements at low temperatures in order to investigate vacancy in single crystal silicon. The longitudinal elastic constants of non-doped and boron-doped silicon grown by a floating zone method exhibit appreciable softening with decreasing temperature down to 20 mK. The softening of boron-doped silicon is easily suppressed in applied magnetic field up to 2 T, while the softening of non-doped silicon is robust in fields even up to 16 T. The softening of elastic constants in high-purity crystalline silicon is certainly caused by the coupling of elastic strains of the ultrasonic waves to electric quadrupoles of the vacancy orbital.

DOI： 10.1088/1742-6596/150/4/042002

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By means of the low-temperature ultrasonic measurement, we try to observe the elastic softening due to the vacancies in as-grown silicon crystals grown by the Czochralski ( CZ) method. We prepared a high-resistivity CZ silicon crystal ingot comprising the following defect-regions: the void region, the region of ring-like oxidation stacking fault, the Pv-region, the Pi-region, and the region of the dislocation clusters. Both of the elastic constants C(44)(T) and [C(11)(T) - C(12)(T)]/2 measured for the samples taken from the Pv-region exhibit the softening of the type CC(T) = C(Gamma)((0)) [1 - Delta(JT)/(T - Theta)] which was also found in our previous study for the non-doped FZ silicon and attributed to the neutral vacancy. No response of the softening to the applied magnetic field is found, as in our previous case of the non-doped FZ silicon. The observed softenings are attributed to the triply degenerate T(2) states of the vacancy accommodating two electrons with anti parallel spins. The samples in the Pi-region exhibit no such softening, confirming that the origin of the softening is the vacancies. A qualitative explanation is given to the measured distribution of the vacancy concentration.

DOI： 10.1007/s10854-008-9715-0

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The off-center rattling of Nd rare-earth ions in the filled skutterudite compound NdOs4Sb12 has been investigated by ultrasonic measurement. The longitudinal C-11 mode for frequencies between 34 and 253MHz shows a marked frequency dependence in elastic constant and ultrasonic attenuations at two different temperatures centered at around 45 and 15K. The relaxational frequency dependence of ultrasonic dispersion reveals a thermally activated Gamma(23)-type off-center motion of Nd-ions, involving local charge fluctuations with Gamma(23) symmetry in the (OsSb3)(4) cage. An attempt time tau(0,(1)) = 7.5 x 10(-12) s and an activation energy E-1 = 337 K were obtained from fits to the dispersion at around 45 K. The presence of another dispersion at lower temperatures of around 15 K implies that the rattling in NdOs4Sb12 has an additional low-energy excitation characterized by a lower activation energy E-2 similar to 67 K with an attempt time tau(0,(2)) = 5.1 x 10(-11) s.

DOI： 10.1143/JPSJ.77.074607

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

A variety of thermodynamic and transport measurements were made on high-quality single crystals of the Pr-based filled skutterudite compound PrFe4As12. Abrupt features in magnetization, ac susceptibility, specific heat, resistivity, thermoelectric power, and ultrasonic velocity reveal the onset of long range ferromagnetic order below Theta(C)=18 K. The low-temperature magnetic susceptibility is characterized by a Curie-Weiss law with an effective moment of 3.52 mu(B)/f.u. and a saturation magnetization of 2.3 mu(B)/f.u., which is consistent with a magnetic Gamma(5) triplet ground state. A gaplike reduction of the large electronic specific heat coefficient of 340 mJ/mol K-2 and several other features point to a strongly correlated electron behavior that is likely coupled to a change in magnetic and/or structural order near T-*similar or equal to 12 K. Furthermore, this complex magnetic state is found to be strongly field dependent, as evidenced by a change in the easy axis at low fields and an additional contribution to thermal conductivity appearing only at high fields.

DOI： 10.1103/PhysRevB.77.144432

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Last five years we have mainly investigated phonons in the following cage compounds by Raman scattering: RT4X12, A(8)Ga(16)Ge(30), La3Pd20Ge6, RB6, KOs2O6. From this systematic investigation we have clarified the following dynamical properties of the guest ion trapped in the large cages. The vibration of the guest ion is highly anharmonic due to weak atomic interaction between the guest ion and cage atom. This anharmonicity universally decreases the vibration energy of the guest ion with decreasing temperature. The existence of carriers decreases the interaction between the guest atoms and changes the dispersion curve of the guest ion mode to flat, which is the experimental evidence of the weak interaction between the guest atoms. For thermoelectricity, it is found in A(8)Ga(16)Ge(30) that the off-center rattling decreases lattice thermal conductivity.

DOI： 10.1143/JPSJS.77SA.142

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We have investigated elastic properties of a garnet-type single crystal Tb3Ga5O12 by ultrasonic measurements. Temperature dependence of the transverse elastic constants (C-11 - C-12)/2 and C-44 shows strong Curie-type softening below 150 K with minima around 30 - 50 K and also below 5 K. These effects are due to quadrupole susceptibilities for the crystalline electric field system with a pseudo-doublet Gamma(3) ground state and an excited triplet Gamma(5) at 57.3 K. Magnetic field dependence of the (C-11 - C-12)/2 mode in H parallel to [110] shows step-like anomaly due to a level crossing at around 9.5 T.

DOI： 10.1143/JPSJS.77SA.269

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Electric quadrupole effects in a Pr-based clathrate compound Pr3Pd20Si6 have been investigated by ultrasonic measurements. Elastic constants of (C-11 - C-12)/2 and C-44 in Pr3Pd20Si6 show curie-type softenings with decreasing temperature below 20 K, which are described in terms of quadrupole effects of 4f-electron for the ground state either Gamma(3) doublet or Gamma(5) triplet. H-T phase diagram of Pr3Pd20Si6 under the magnetic fields along [110] is obtained from elastic anomalies in (C-11 - C-12)/2 mode.

DOI： 10.1143/JPSJS.77SA.263

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Off-center rattling of La-ion in the filled skutterudite compound LaOs4Sb12 has been investigated by means of ultrasonic measurements. An elastic constant C-11 shows a remarkable frequency dependence in elastic constant and ultrasonic attenuation at around 25 K. This frequency dependent ultrasonic dispersion reveals thermally activated Gamma(23)-type off-center rattling of La-ion. An attempt time tau(0) = 5.0x10(-11) sec and an activation energy E = 127 K were obtained from the analysis.

DOI： 10.1143/JPSJS.77SA.242

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：TRANS TECH PUBLICATIONS LTD  

The low-temperature ultrasonic experiments are performed to measure the distribution of vacancy concentration in the ingot of the Czochralski (CZ) silicon crystal grown with the pulling rate gradually lowered. The elastic softening similar to that we recently found for the floating-zone-grown silicon crystals is observed for the so-called vacancy-rich region of the ingot which contains no voids or dislocation clusters. We further uncover that the interstitial-rich region in the ingot exhibits no such elastic softening, confirming our previous conclusion that the defects responsible for the low-temperature elastic softening are the vacancies. We also disclose that the elastic softening is absent for the ring-like oxidation stacking fault (R-OSF) region of the ingot. The measured distribution of the vacancy concentration indicates that the minority point defects are perfectly cancelled by the majority point defects during the CZ crystal growth.

DOI： 10.4028/www.scientific.net/SSP.131-133.455

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By means of the low-temperature ultrasonic measurements, we try to observe the single vacancies in the as-grown Czochralski (CZ) silicon crystal of high resistivity and commercial-base quality. The crystal ingot we adopt here is grown with the pulling rate gradually lowered to produce various regions of different point-defect states. The elastic constants C-T2g(T) and C-Eg(7) measured for the samples taken from the Pv-region exhibit the softening of the type C-Gamma(T) = C-Gamma((0)) [1-Delta(JT)/(T-Theta)] which was found in our previous study for the non-doped FZ silicon and attributed to the neutral vacancy. The response of the softening to the applied magnetic field is found to be the same as in the case of the non-doped FZ silicon. The samples in the Pi-region exhibit no such softening, confirming that the origin of the softening is due to the vacancies. A qualitative explanation is given to the measured distribution of the vacancy concentration. For the CZ silicon crystals, the vacancies can be well observed for the Pv-region only. (C) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2007.08.131

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We have successfully observed isolated vacancies in crystalline silicon using low-temperature ultrasonic measurements. The floating zone (FZ) silicon exhibits softening in longitudinal elastic constants consisting of transverse C-44 and (C-11-C-12)/2 in part with decreasing temperature below 20 K down to 20 mK. The applied magnetic fields of up to 16 T at the base temperature 20 mK show no effect on the low-temperature softening in non-doped FZ silicon, while the fields of up to 2 T suppress the low-temperature softening in boron-doped FZ silicon. This experiment suggests that isolated vacancies with non-magnetic charge state V-0 in the non-doped FZ silicon and with magnetic charge state V+ in the boron-doped FZ silicon lead to the low-temperature softening. We have also observed the low-temperature softening in the Pv-region of non-doped Czochralski (CZ) silicon ingot, which indicates vacancy distribution. A coupling of electric quadrupoles of triplet state of vacancy orbital to the elastic strains of the sound waves is discussed for description of the low-temperature softening. (C) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2007.08.124

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We have investigated elastic properties of a single crystal PrPb3 showing antiferro-quadrupole (AFQ) ordering at T-Q = 0.4K using ultrasonic measurements. Since the crystalline-electric-field (CEF) ground state of PrPb3 is a non- Kramers Gamma(3) doublet having quadrupolar moments O-2(0) and O-2(2), the temperature dependence of a transverse (C-11 - C-12)/2 mode shows a curie- type softening with decreasing temperature toward T-Q. Furthermore, an anomaly accompanying a lock-in transition of AFQ ordering was observed in (C-11 - C-12)/2 on PrPb3 at 250mK. In the case of Pr0.98La0.02Pb3, (C-11 - C-12)/2 exhibits softening with decreasing temperature and shows a broad minimum at 330 mK. We have observed a large attenuation of the (C-11 - C-12)/2 mode in applying magnetic fields up to 13 T. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2006.10.002

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We have performed ultrasonic measurements under high magnetic fields up to 30T by using the hybrid magnet at the National Institute for Materials Science to investigate the magnetic phase diagram for antiferroquadrupole (AFQ) phase II in CexLa1-xB6. With increasing Ce concentration x from x = 0.50, the AFQ phase transition temperatures T-Q indicate an almost linear increase in various fields. The large magnetic anisotropy of AFQ phase II, in which T-Q(H) (parallel to 001]) is much smaller than T-Q(H) (parallel to 110]) and T-Q(H) (parallel to 111]) in high magnetic fields, is revealed in x = 0.75; 0.60 as well as in x = 0.50. These experimental results support the theoretical calculation based on the Gamma(5)-type AFQ ordering and the magnetic field induced octupole T-xyz. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2006.10.126

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Elastic constants of filled-skutterudite NdOs4Sb12 single crystals have been investigated by means of ultrasonic measurements. Transverse C-44 and longitudinal C-11 modes show Curie-type softening, which is proportional to the reciprocal temperature from 10K down to 0.9K. This softening can be explained in terms of the quadrupolar susceptibility modified by crystalline electric field with a Gamma(8) quartet ground state in O-h symmetry. The C-11 mode also shows a broad shoulder and a small dip around 45 and 13 K, respectively. A Debye-type frequency dependence of the anomalies in the longitudinal C-11 mode resembles an ultrasonic dispersion in PrOs4Sb12, which is expected to be due to the "rattling'' effect, a thermally activated off-center motion of the rare-earth atom in the Sb-cage. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2006.10.010

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

We have carried out an ultrasonic measurement to investigate an off-center motion of a rare-earth ion in clathrate compounds R3Pd20Si6 and R3Pd20Ge6. In R3Pd20Ge6, an elastic constant C-44 shows an ultrasonic dispersion around 10-30 K. This is caused by thermally activated rattling of the rare-earth ion over an anharmonic potential in the cage. In addition, the C-44 of La3Pd20Ge6 exhibits a remarkable softening proportional to 1/T below 3K down to 20 mK. This result indicates the tunneling state of the rare-earth ion through the potential barrier. On the other hand, the C-44 of La3Pd20Si6 and Ce3Pd20Si6 shows no ultrasonic dispersion indicating the absence of the rattling. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2006.10.329

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DOI： 10.1103/PhysRevB.76.014527

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Other Link： http://orcid.org/0000-0002-0957-3396

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

We carried out sub-Kelvin ultrasonic measurements for observation of vacancies in crystalline silicon. The longitudinal elastic constants of non-doped and B-doped floating zone (FZ) silicon crystals in commercial base revealed low-temperature elastic softening below 20 K. The applied magnetic fields turns the softening of the B-doped FZ silicon to a temperature-independent behavior, while the fields up to 16 T at base temperature 20 mK make no effect on the softening of the non-doped FZ silicon. This result means that the vacancy accompanying the non-magnetic charge state V-0 in the non-doped silicon and the magnetic V+ in the B-doped silicon is responsible for the low-temperature softening through the Jahn-Teller effect. The direct observation of the vacancy using the sub-Kelvin ultrasonic measurements advances point defects controlling in silicon wafers and semiconductor devices. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.mseb.2006.07.038

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The low-temperature ultrasonic measurements are performed for the direct observation of the vacancies in Czochralski-grown (CZ-grown) silicon crystal. The elastic softening similar to that we recently found for the floating-zone-grown (FZ-grown) silicon crystals is observed also for the vacancy-rich region of the defect-free zone (DFZ) in the CZ silicon crystal. We further uncover that both of the interstitial -rich region in the DFZ and the region of the ring-like oxidation-induced stacking faults of the same crystal ingot exhibit no such elastic softening of detectable magnitude, confirming our previous conclusion that the defects responsible for the low-temperature softening are the vacancies. We observe how the vacancy concentration in the DFZ varies along the pulling direction. (c) 2006 Published by Elsevier B.V.

DOI： 10.1016/j.mseb.2006.07.032

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

We have investigated an off-center local oscillator of a guest atom in cage of clathrate compounds R3Pd20Ge6 (R = La, Ce, Pr, Nd) and a filled skutterudite PrOs4Sb12 using ultrasonic measurements. The observation of ultrasonic dispersions in transverse C-44 mode of R3Pd20Ge6 and in transverse (C-11 - C-12)/2 mode of PrOs4Sb12 revealed the rattling of the off-center oscillator characterized by a relaxation time with Arrhenius-type temperature dependence. A low-temperature softening of C-44 in La3Pd20Ge6 below 3 K down to 20 mK and a softening of (C-11 - C-12)/2 in PrOs4Sb12 above the heavy Fermion superconducting transition indicate the charge fluctuation due to the degenerate off-center oscillators. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2006.03.071

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Magnetization, specific heat, and electrical resistivity measurements were made on single crystals of the filled skutterudite compound Pr Os4 As12. Specific heat measurements indicate an electronic specific heat coefficient γ∼50-200 mJ mol K2 at temperatures 10 K≤T≤18 K, and ∼1 J mol K2 for T≤1.6 K. The combined measurements reveal the presence of two, or possibly three, ordered phases at temperatures below ∼2.3 K and in fields below ∼3 T. The low temperature phase displays antiferromagnetic characteristics, while the nature of the ordering in the other phase(s) has yet to be determined. © 2006 The American Physical Society.

DOI： 10.1103/PhysRevB.73.144409

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

The magnetic phase diagram for antiferroquadrupole (AFQ) ordering in tetragonal HoB2C2 has been investigated by measurements of elastic constants C-11, C-44, and C-66 in fields along the basal x-y plane as well as the principal [001]-axis. The hybrid magnet (GAMA) in Tsukuba Magnetic Laboratory was employed for high field measurements up to 30 T. The AFQ phase is no longer observed above 26.3 T along the principal [001]-axis in contrast to the relatively small critical field of 3.9 T in fields applied along the basal [110]-axis. The quadrupolar intersite interaction of O-xy and/or O-2(2) is consistent with the anisotropy in the magnetic phase diagram of the AFQ phase in HoB2C2.

DOI： 10.1103/PhysRevB.71.104416

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

The elastic properties of HoB2C2 undergoing an antiferroquadrupole ordering with a tetragonal structure have been investigated by means of ultrasonic measurements. The transverse (C-11-C-12)/2, C-44, and C-66 modes exhibit characteristic softenings with decreasing temperature in a paramagnetic phase I down to an ordered phase IV at T-C1=5.9 K. The softening of (C-11-C-12)/2, C-44 and C-66 is described by a formula C-Gamma=C-Gamma(0)(T-T-C(0))/(T-Theta) due to the quadrupole-strain interaction for the 4f state of HoB2C2 consisting of a ground E doublet with orbital degeneracy and an excited singlet with a small-energy splitting Delta. The significant softening of the elastic constant and the ultrasonic attenuation in phase IV between T-C1=5.9 K and T-C2=5.0 K have been found. The ultrasonic dispersion in phase IV indicates the slowing down of the quadrupole fluctuation time, tau=7x10(-9) sec.

DOI： 10.1103/PhysRevB.67.115129

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ACTA PHYSICA POLONICA B, JAGELLONIAN UNIV, INST PHYSICS  

The antiferroquadrupole orderings of the ternary rare earth compounds HoB2C2 and DyB2C2 have been investigated by means of ultrasonic measurements. The transverse (C-11-C-12)/2, C-44, C-66 modes in HoB2C2 exhibit characteristic softening above T-c2 = 5.0 K, which consist with an E-doublet and a singlet for the ground state. Considerable elastic softening and ultrasonic attenuation in phase IV below T-c1 = 5.9 K of HoB2C2 indicates an enhancement of the quadrupole fluctuation with a relaxation rate tau = 7 x 10(-9) sec. A softening of the transverse elastic constant C-44 in DyB2C2 above T-Q = 24.7 K indicates accidentally degenerated Kramers doublets of E-1/2 and E-3/2 for the ground state.

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We have made low-temperature thermal expansion and magnetostriction measurements on the Kongo compound Ce0.75La0.25B6. With decreasing temperature, Ce0.75La0.25B6 in phase IV expands along the [0011 axis and shrinks along the r1111 axis, A tiny anisotropic distortion is found in this phase. Probably, some kinds of macroscopic symmetry are breaking in phase IV.

DOI： 10.1143/JPSJS.71S.115

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We have performed low-temperature ultrasonic measurements on CeRu2Si2 by using a dilution refrigerator down to 20 niK with a superconducting magnet up to 16 T. The longitudinal modes exhibit huge softening of 20% around a metamagnetic transition point H-C similar to 7.7 T, while the transverse modes show softening of about 1%. This result suggests that the coupling of the volume strain epsilon(B) to the order parameter with total symmetry plays a crucial role for the metamagnetic.transition in CeRu2Si2. In the vicinity of H-C, the enormous ultrasonic attenuation has been observed in the longitudinal ultrasonic modes. The relaxation time tau increases considerably near the metamagnetic transition due to a critical stowing-down. We also show the detailed magnetic phase diagram of CeRu2Si2 down to 20 mK around H-C.

DOI： 10.1143/JPSJS.71S.267

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We have investigated charge and orbital (quadrupolar) ordering in perovskite manganites Pr1-xCaxMnO3 (x = 0.35, 0.40, 0.50) by ultrasonic measurements. Only transverse (C-11-C-12)/2 mode of the;-r, = 0.35, 0.40 and 0.50 compounds shows a softening from 400 K down to the charge ordering point T-co = 220 240 K. Tins softening is originated from the bilinear coupling of the quadrupole moment of the eg orbital in Mn3+ ion to the elastic strain. Furthermore, the elastic softening in both (C-11 = C-12)/2 and C-44 modes due to the coupling of the charge fluctuation mode to elastic strain is observed just above T-co, especially for the x = 0.50 compound. The considerable magnetic field dependence of the elastic constants is obseved. In particular, the magnetic fields up to 12 T releases completely the elastic softening of (C-11 - C-12)/2 mode due to the fact that the charge fluctuation is suppressed under 12 T in the = 0.40 compound.

DOI： 10.1143/JPSJS.71S.139

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Charge ordering in Yb4As3 and Sm3Te4, complementary f-electron compounds with the same crystalline structure, is investigated on the basis of a Coulomb lattice gas model; the Coulomb interactions between ions are fully taken into account within a classical treatment. The Madelung energy of the system at finite temperatures is calculated with a Monte Carlo (MC) method simulating the Boltzmann distribution of multivalent cations on equivalent lattice sites. The unit cell for the MC simulations is extended to contain 32 molecular formulas in it. The model is successful in distinguishing the two mixed-valence compounds with different, characteristics of charge ordering. Yb4As3 shows a phase transition (Verwey transition) due to charge ordering while Sm3Te4 continuously freezes into a glassy state on cooling.

DOI： 10.1143/JPSJS.71S.306

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

We have investigated the elastic constants of the ternary rare earth compound HoB2C2 with a tetragonal structure, by means of the ultrasonic method. The elastic constants of (C-11- C-12)/2, C-44 and C-66,, corresponding to the transverse ultrasonic modes exhibit the softening proportional to reciprocal temperature below about 40 K. This softening is commonly enhanced in the ordered phase IV below T-C1 = 5.9 K. An abrupt increase of elastic constants is found in the ordered phase UI below T-C2 = 5,0 K characterized by the simultaneous antiferro-type ordering of electric quadrupole and magnetic dipole moments. The quadrupole susceptibility based on a model consisting of a ground state E-doublet and an excited singlet with a low energy in HoB2C2 is employed for the analysis of the softening above T-C1 = 5.9 K. The enhancement of the elastic softening in the phase IV of HoB2C2 resembles to the soft C44 mode in the phase IV in Ce0,751La0.25B6.

DOI： 10.1143/JPSJS.71S.88

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

Anisotropy in the magnetic phase diagrams (H-T plane) of CexLa1-xB6 and the Ce concentration dependence of the magnetic phase diagrams are presented. Phase boundaries of phase IV in the diagrams are isotropic. Present results suggest the absence of quadrupolar degeneracy in phase IV. Field induced antiferromagnctism is shown in CexLa1-xB6.

DOI： 10.1143/JPSJS.71S.112

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER INST PHYSICS  

We made the ultrasonic measurements on the perovskite manganese La1-xSrxMnO3 (x = 0.12, 0.165) to examine the electron-lattice interaction in the system with both orbital and charge degrees of freedom. The softening of (C-11 - C-12)/2 above the structural transition point T-s = 290 K for x = 0.12 and T-s = 310 K for x = 0.165 is well described in terms of the quadrupolar susceptibility for O-2(0) and O-2(2) of d gamma -doublet of Mn3+. Elastic softening associated with the charge ordering of Mn4+ ions in a sea of Mn3+ ions for x = 0.12 and x = 0.165 is also presented.

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We have carried out ultrasonic measurements of a boron-doped silicon ingot grown by the Czochralski method in order to determine the quadrupole-strain interaction constant of a vacancy orbital. The low-temperature softening of the elastic constant C-44 shows a remarkable variation depending on positions of the ingot, which reflects the distribution of vacancy concentration N in the ingot. An infrared laser scattering tomograph was employed to measure the density and size of voids in the silicon wafers by determining the vacancy concentration N-cons consumed in void formation. Using a combination of laser scattering tomography and low-temperature softening, we have found a sum rule in which the initially created vacancy concentration N-total corresponds to the sum of the residual vacancy concentration N and the consumed vacancy concentration N-cons as N-total N + N-cons. Taking account of the sum rule, we deduce the interaction constant g(Gamma 5) = (2.8 +/- 0.2) x 10(5) K for the quadrupole-strain interaction H-QS = -g(Gamma 5)O(zx)epsilon(zx) of the vacancy orbital. The huge deformation energy of 1.6 x 10(5) K per vacancy with the Gamma(8) ground state for unit strain epsilon(zx) = 1 verified the strong electron-lattice interaction of the vacancy orbital. Employing the one-to-one correspondence between the softening of Delta C-44/C-44 = 1.0 x 10(-4) down to 30 mK and the vacancy concentration of N = 1.5 x 10(13) cm(-3), we can determine the vacancy concentration by low-temperature ultrasonic measurements. The present work surely puts forward a novel semiconductor technology based on low-temperature ultrasonic measurements for evaluating vacancy concentration in silicon wafers.

DOI： 10.7566/JPSJ.82.124604

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