Yoshizawa Hideki

Study of Neutron Diffraction on 154SmRu4P12 Single Crystal

The magnetic structure of SmRu 4 P 12 has been investigated by neutron diffraction. Long-range antiferromagnetic ordering with a propagating vector of q =(1,0,0) was observed below the metal–insulator transition temperature ( T MI =16.5 K). Data obtained at T =3.3 K were analyzed with dipole magnetic moments of µ=0.30 µ B at Sm sites. The results suggest that the primary order parameter is the T α , or T β octupole accompanied by strong mixing with T α and dipoles.

Phonon Dynamics of Type-I Clathrate Sr8Ga16Ge30 Studied by Inelastic Neutron Scattering

The phonon dynamics of type-I clathrates Sr 8 Ga 16 Ge 30 have been studied at room temperature by inelastic neutron scattering. Optical phonons associated with large vibrations of Sr atoms in large tetrakaidecahedral cages, (Ga,Ge) 24 , are observed at a relatively low energy of E ∼4 meV. Analysis based on a Born–von Karman force model shows that the longitudinal force constants between the Sr atoms and the oversized cages has a small value of about 0.008 mdyn/A. The results indicate that the Sr atoms are very loosely bound to the surrounding oversized cages.

Neutron Scattering Study of Antiferromagnetic Order in the Heavy Fermion CeInCu2

Neutron scattering experiment on a single crystal of the heavy-fermion system CeInCu 2 demonstrated the occurrence of the magnetic order below 2 K which was found by the previous NMR measurement. The magnetic order is a short-range order of the type 1 structure of an fcc antiferromagnet in which moments parallel to (0 0 1) are modulated in the [0 0 1] direction. The moment estimated from the integrated intensity is µ=0.40±0.07 µ B , which is about one half of the moment of the \(\varGamma_{7}\) ground state.

Effects of Uniaxial Stress on Antiferromagnetic Moment in the Heavy Electron Compound URu2Si2

We have performed the elastic neutron scattering experiments under uniaxial stress σ along the tetragonal [100], [110] and [001] directions for URu 2 Si 2 . For σ∥[100] and [110], the antiferromagnetic moment µ o is strongly enhanced from 0.02 µ B /U (σ=0) to 0.22 µ B /U (σ=0.25 GPa) at 1.5 K. The rate of increase ∂µ o /∂σ is roughly estimated to be ∼1.0 µ B /GPa, which is much larger than that for the hydrostatic pressure (∼0.25 µ B /GPa). Above 0.25 GPa, µ o shows a tendency to saturate similar to the behavior in the hydrostatic pressure. For σ∥[001], on the other hand, µ o shows only a slight increase to 0.028 µ B /U (σ=0.46 GPa) with a rate of ∼0.02 µ B /GPa. The observed anisotropy suggests that the competition between the hidden order and the antiferromagnetic state in URu 2 Si 2 is strongly coupled with the tetragonal four-fold symmetry and the c / a ratio, or both.We have performed the elastic neutron scattering experiments under uniaxial stress \sigma along the tetragonal [100], [110] and [001] directions for URu2Si2. For \sigma // [100] and [110], the antiferromagnetic moment \mu_o is strongly enhanced from 0.02 \mu_B (\sigma=0) to 0.22 \mu_B (\sigma=2.5 kbar) at 1.5 K. The rate of increase d\mu_o/d\sigma is roughly estimated to be ~ 0.1 \mu_B/kbar, which is much larger than that for the hydrostatic pressure (~ 0.025 \mu_B/kbar). Above 2.5 kbar, \mu_o shows a tendency to saturate similar to the behavior in the hydrostatic pressure. For \sigma // [001], on the other hand, \mu_o shows only a slight increase to 0.028 \mu_B (\sigma = 4.6 kbar) with a rate of ~ 0.002 \mu_B/kbar. The observed anisotropy suggests that the competition between the hidden order and the antiferromagnetic state in URu2Si2 is strongly coupled with the tetragonal four-fold symmetry and the c/a ratio, or both.

Progress in High Resolution Chopper Spectrometer, HRC

The High Resolution Chopper Spectrometer (HRC) was installed at J-PARC, to study dynamics in condensed matters with high-resolutions and relatively-high-energy neutrons. Although the HRC was damaged by the earthquake disaster, we recovered and started neutron scattering experiments. During the recovery works, we also improved the performance of the HRC, by installing a supermirror guide tube, a collimator system, an experiment control environment etc.

Development of a Hybrid CuBe/NiCrAl Clamp-Type High Pressure Cell for Neutron Diffraction

A small hybrid CuBe/NiCrAl piston–cylinder-type high-pressure (HP) clamp cell was designed for low-temperature (LT) neutron diffraction (ND) measurements, and its characteristics was evaluated through various parameters which include cooling performance, transmission efficiency for neutrons. The cell successfully produces pressure up to 2.5 GPa at room temperature (RT).

Weak Ferromagnetism and Multiple Metamagnetic Transitions in the Non-centrosymmetric Tetragonal Compound CePdSi3

We have succeeded in growing single crystalline samples of CePdSi3 with the BaNiSn3-type non-centrosymmetric structure. Specific heat, magnetic susceptibility, and magnetization measurements were carried out, which revealed three successive magnetic transitions at TI = 4.85(5) K, TII = 2.78(5) K, and TIII = 2.30(5) K at zero field. Below TII, a weak ferromagnetic component was observed, indicating a canted antiferromagnetic ground state in CePdSi3. The observed large magnetic anisotropy in CePdSi3 was explained in terms of a simple crystalline-electric-field model. From the magnetization measurements, we identified five (three) magnetic states in the H–T phase diagrams for the H || [100] ([001]) direction. Interestingly, only three magnetization steps were observed for H || [110], suggesting the existence of the in-plane magnetic anisotropy in CePdSi3. We discuss a possible nature of the complex magnetic properties of CePdSi3.

Influence of Quasi-Bi-Stripe Charge Order on Resistivity and Magnetism in the Bilayer Manganite La 2- 2xSr 1+ 2xMn 2O 7

The charge ordering in the bilayer manganite system La

Heterogeneous Metallic State in URu2Si2

_{2-2x}

Anisotropic Pressure Effects on Superconductivity in Fe1+yTe1−xSx

Sr