Development of pressure cell for specific heat measurement at low temperature and high Magnetic field.

We report the performance of Ag-Pd-Cu alloy as the material of a pressure cell to carry out specific heat measurements at low temperatures and high magnetic fields. The Ag-Pd-Cu alloy is advantageous to reduce the background due to the nuclear specific heat in the pressure cell growing at low temperatures and high magnetic fields. We prepared 70-20-10 alloy composed of 70 mass % of Ag, 20 mass % of Pd, and 10 mass % of Cu. The maximum hardness over 100 HRB (Rockwell-B scale) is achieved by the heat treatment. The magnetization and susceptibility results show that the alloy includes a small amount of magnetic ions, whose concentration is smaller than that in the Be-Cu alloy. We confirm that the specific heat of a piston cylinder cell made of the 70-20-10 alloy increases smoothly from 0.2 to 9 K and the nuclear specific heat decreases drastically in magnetic field compared to that expected in the Be-Cu alloy. The pressure value in the cell at low temperature increases almost linearly up to P=0.4 GPa, which is nearly the limit of the inner piston made of the 70-20-10 alloy, with increasing of the load applied at room temperature.

Pressure-induced enhancement of giant magnetoresistance due to crossover of interlayer exchange coupling in Fe/Cr multilayers.

We report the first observation of a large pressure-induced enhancement of giant magnetoresistance (GMR) in magnetic multilayers (MML). In Fe/Cr MMLs with the Cr layer thickness of approximately 30 A, a crossover from biquadratic to bilinear interlayer exchange coupling (IEC) was observed by applying pressure, and simultaneously the GMR under high pressure (>2 GPa) was enhanced to be twice as large as that at ambient pressure. The enhanced GMR is attributed to the suppression of the biquadratic IEC by applying pressure, and the electrical resistivity in parallel alignment of magnetization also showed a crossover behavior, suggesting an electronic origin for the observed pressure effects.

The effect of pressure on the low energy spin fluctuations in CeAl(2) investigated through (27)Al nuclear quadrupole resonance and nuclear magnetic resonance measurements.

To microscopically elucidate the initial evolution of the electronic and magnetic states of a Kondo compound CeAl(2) (Néel temperature T(N)∼3.8 K) from the antiferromagnetically ordered state with a spin density wave to a magnetic quantum critical point with the application of pressure P, we have carried out (27)Al nuclear quadrupole resonance and magnetic resonance measurements for P = 0 and 2.5 GPa. The Knight shift, which is proportional to the uniform susceptibility [Formula: see text], exhibits a rapid increase below ∼50 K down to T(N) for each pressure, indicating that the sufficiently localized f electron does not directly participate in the formation of the Fermi surface even at P = 2.5 GPa. The nuclear spin-lattice relaxation measurements and the analysis lead to the conclusion that the cf hybridized band with a rather large density of states at the Fermi level is formed below an onset temperature above T(N), the value of which increases with the application of pressure. The relaxation rate in the paramagnetic state is dominated by the generalized susceptibility [Formula: see text] that has peaks near the antiferromagnetic wavevector [Formula: see text] associated with the nesting properties of the Fermi surface of the underlying cf hybridized band. With decreasing temperature, [Formula: see text] also exhibits a significant increase larger than that of χ(0). The finite pressure of 2.5 GPa has the effect of reducing both χ(0) and χ(Q(AF)) by about 20% in their magnitudes. Then, changes in the nesting condition with pressure are conjectured to play an important role in depressing the magnetic ordering, in addition to the increase in the extent of mixing J(cf) between the localized f electrons and conduction electrons.

Residual short-range order in the heavy fermion compound CeInCu2.

By using the X-ray diffraction technique, residual short-range order was detected in CeInCu(2), cerium dicopper indium, which is known to be a heavy fermion compound. In spite of the long-range order of this substance, diffuse scattering exhibiting short-range order was observed at room temperature. The correlation parameters obtained showed that an incorrectly occupied lattice site has a tendency to gather atoms of different species at the neighboring sites along the <111> directions. Thus, the disordered region would form a cluster composed of several disordered atoms. Furthermore, a chain-type correlation which has a period of 20-23 Å along the same directions was indicated. The superstructure-like feature of the disordered atoms hardly increases the residual resistivity. It is consistent with the behavior of the residual resistivity under high pressure.

High-pressure system for Compton scattering experiments.

High-pressure apparatus for Compton scattering experiments has been developed to study the momentum distribution of conduction electrons in metals and alloys at high pressure. This apparatus was applied to observe the Compton profile of metallic Li under pressure. It was found that the Compton profile at high pressure could be obtained within several hours by using this apparatus and synchrotron radiation. The result on the pressure dependence of the Fermi momentum of Li obtained here is in good agreement with that predicted from the free-electron model.