Yasuhisa Ushida

Thermal expansion measurement under pressure of UGe2

Abstract Volume expansion measurements of single crystalline UGe 2 samples have been made under pressure. The linear coefficient α V ( T ) at ambient pressure shows a broad hump at around T x ∼25 K and a sharp transition at T C =52 K. We have observed that the anomaly in Δ α V at T x becomes prominent and increases in magnitude with increasing pressure.

Experimental study on metamagnetism in Ce5Si3

We have measured specific heat in magnetic fields, magnetization at ambient and high pressures and magnetostriction of Ce 5 Si 3 and its alloy system (Ce 1- x La x ) 5 Si 3 . As temperature is lowe...

Magnetic and superconducting properties under high pressure in URu2Si2

URu2Si2 exhibits successive phase transitions at Tc (superconducting) and at T0 (hidden) at ambient pressure. We have made thermal expansion measurements under pressure for a well-characterized single crystalline sample of URu2Si2. We have observed that an additional anomaly appears between Tc and T0 only under high pressures. From the pressure dependence of these temperatures, we have constructed a P–T phase diagram.

Non-Fermi-liquid behavior in amorphous UPd2Al3

Abstract To investigate the relation between the non-Fermi-liquid state and the disordered state, a crystallographically disordered amorphous UPd2Al3 has been prepared. At low temperatures, the measured electronic specific heat coefficient γ has a typical temperature dependence of non-Fermi-liquid state, γ∝− log T .

High Pressure Magnetization Measurements on URu2Si2.

We have made high pressure magnetization measurements on a single crystalline URu 2 Si 2 up to P = 1.61 GPa, in magnetic fields up to 15 T and in the temperature range between 4.2 and 100 K. A characteristic temperature T 0 which corresponds to an antiferromagnetic phase transition shows a slight increase with pressure, while T max , at which the temperature dependence of the magnetization exhibits a maximum, remains nearly constant with pressure. We have also observed that the pressure dependence of the high field magnetization at low temperatures shows a shallow minimum at around 1 GPa, in contrast to a strong and monotonic increase in a staggered magnetic moment revealed by recent elastic neutron diffraction experiments under pressures. To reconcile this discrepancy, we suggest, in conjunction with other experimental results, that the observed large staggered moment in the neutron diffraction experiments is not static but fluctuating in time.

Magnetic properties of (Ce1− xLa x)5Si2.69

Abstract Ce 5 Si 3 , which possesses two inequivalent Ce sites, Ce1 and Ce2, shows two anomalies in the magnetic susceptibility and specific heat, and a meta-magnetic jump in the magnetization curve. In order to reveal the origin of the two low temperature anomalies and the meta-magnetism, AC magnetic susceptibility and magnetization measurements have been performed on (Ce 1− x La x ) 5 Si 2.69 . By increasing x , the non-magnetic ground state in Ce2 changes into a magnetic one with ferromagnetic correlation at around x = 0.1. The antiferromagnetic (AF) ordering in Ce1 and the meta-magnetism suddenly disappear for x ≥ 0.1. These results suggest that the meta-magnetism is closely related with the AF ordering as well as the low-temperature anomalies.

Metamagnetism and low-temperature properties of Ce5Si3☆

Abstract Tetragonal Cr 5 B 3 -type Ce 5 Si 3 shows a metamagnetic jump in the magnetization curve around 40 kOe at 1.3 K. In order to clarify the mechanism we performed specific heat, AC magnetic susceptibility and magnetization measurements on polycrystalline Ce 5 Si 3-δ (0 ⩽ δ ⩽ 1) and (Ce 1− x La x ) 5 Si 3-δ (0 ⩽ x ⩽ 1) in magnetic fields up to 150 kOe and in temperatures down to 0.4 K. The magnetic properties were hardly affected with δ, but strongly affected with x . For x = 0.25, the metamagnetism disappeared completely. Anomalous low temperature behavior including the metamagnetism is discussed in connection with a Ce-dimer model with ground singlet and excited triplet states.

Construction of a 3He cryostat using a charcoal sorption pump

Abstract A superconducting transition temperature of a typical heavy fermion superconductor is lower than 1 K . Therefore it is needed to perform measurements at a low temperature below 1 K . For this purpose, we have constructed a highly simple 3 He cryostat using a charcoal sorption pump, instead of using a rotary vacuum pump. We have found that a sample cools down to 0.31 K within 30 min after transferring liquid 4 He into the cryostat.

Magnetic susceptibility of amorphous UPd2Al3

Abstract Amorphous UPd 2 Al 3 was made by sputtering method. Magnetic susceptibility χ and magnetoresistance were measured. χ shows the typical cusp due to spin glass transition. AF interaction is suppressed by amorphous disordering.