Hideoki Kadomatsu

Simple clamp pressure cell up to 30 kbar

A design of simple clamp type pressure apparatus utilized for measurements of magnetic susceptibility and electrical resistivity at low temperatures is presented. The cell consists of WC piston and Be–Cu cylinder which was autofrettage processed, and sample cavity consists of a teflon bucket and an electrode plug. In a temperature range from 300 K down to 77 K, pressure was determined by manganin gauge which was calibrated by Bi I→II transition pressure at room temperature and also the temperature dependence of pressure coefficient of manganin resistance was taken into account. As a result, the cell was capable of generating hydrostatic pressures up to 30 kbar at room temperature and at least up to 25 kbar at 4.2 K.

Non-Fermi-liquid behaviour at the pressure-induced antiferromagnetic to nonmagnetic transition in a heavy-fermion compound,

High-pressure studies of transport, magnetic and thermal properties of a heavy-fermion antiferromagnet, , are reviewed. At ambient pressure, the Ce ions in the three nonequivalent sites in this compound are found to be very close to trivalent from -XANES (x-ray absorption near-edge structure) spectra and magnetic susceptibility measurements. With increasing pressure, (1.8 K at P = 0) of is suppressed and vanishes near . Non-Fermi-liquid (NFL) behaviour appears around 0.4 GPa in both the specific heat and AC magnetic susceptibility: and ). Above 0.62 GPa, the normal Fermi liquid state recovers as indicated by the T independence of and the dependence of magnetic resistivity. The variation of with pressure is analysed in terms of two models: the impurity Kondo model with three Kondo temperatures and the self-consistent renormalization (SCR) theory of spin fluctuations (SFs). We find that the crossover in is better described by the SCR theory. The characteristic SF temperature increases by a factor of 20 for 0.33 GPa , yielding a large Gruneisen parameter around 0.4 GPa.

Magnetocrystalline anisotropy and magnetostriction of Pd-Co alloys

Abstract Magnetocrystalline anisotropy and magnetorestriction have been studied for fcc Pd-Co alloys. There is a difference in the concentration dependences between the two regions divided near 50 at% Pd where the hyperfine field changes the sign. In the Co-rich region, they are gentle, while they are steep in the Pd-rich region accompanying the maxima around 15–20 at % Co.

Pressure-induced magnetic transition in Fe2P

Abstract The weak field ac susceptibility and the resistivity of Fe 2 P single crystals were measured as functions of temperature from 4.2–300 K and as functions of hydrostatic pressures up to 20 kbar, using a newly designed clamp-type pressure cell. The Curie temperature, and the first-order transition temperature, decreased rapidly with increasing pressure, and ferromagnetism vanished at about 13 kbar at 0 K. A second-order transition temperature, as well as the first-order transition, appeared in the region below 170 K and above 5 kbar (triple point) and a new pressure-induced magnetic phase was found. The phase is proposed to be antiferromagnetic for reasons discussed in the paper.

Pressure-Induced Antiferromagnetism of Fe2P

The magnetization of Fe 2 P single crystal was measured as a function of magnetic field H , temperature T and hydrostatic pressure p , for 0≤ H ≤20 kOe, 4.2K≤ T ≤260 K and 0≤ p ≤14 kbar. It was found that the pressure-induced new magnetic phase below T =170 K and above p =5 kbar is the antiferromagnetic with one and unusual two steps metamagnetic behaviours. H - T magnetic phase diagrams were obtained at various pressures and they contains ferromagnetic, antiferromagnetic, intermediate and paramagnetic phases. In contrast with the drastic change in the Curie temperature with pressure, the magnetization at 4.2 K was pressure-insensitive. The pressure-induced magnetic transition and the antiferromagnetism of Fe 2 P are qualitatively discussed on the basis of the competition between the two different interactions and of the itinerant electron theory recently developed.

Magnetic and Structural Properties of CeAg at High Pressure

Electrical resistivity of the cubic CsCl-type ferromagnetic compound CeAg was measured at hydrostatic pressures p s up to 18 kbar and in temperatures from 1.6 K to 300 K. For p <2.2 kbar, the structural transition temperature from cubic to tetragonal was not accompanied with hysteresis and was pressure independent. For p ≥2.2 kbar, the transition temperature increased largely with p , accompanied with wide hysteresis. These trends of pressure dependences are discussed based on the Jahn-Teller distortion model in reference to the alloying effect, CeAg 1- x In x . The Curie temperature T c increased rather rapidly at 2.2 kbar and took a maximum value around 7 kbar. The spin disordered resistivity increased rapidly at 2.2 kbar, but linearly with relatively small gradient above it. The correlation between magnetic and structural transition phenomena are analysed qualitatively, by taking above-mentioned results into account.

Magnetostriction of Pd-Co Alloys

Magnetostriction constants h 1 and h 2 of Pd-Co alloys containing 5∼60 at%Co have been measured in the temperature range between 77 K and 300 K. The values of h 1 and h 2 at 0 K determined by the extrapolation increase in magnitude with increasing Co concentration, and reach the maxima of about -3.1 ×10 -4 and -2.9 ×10 -4 at about 15 at%Co, respectively. With further increase of Co, h 1 decreases rapidly in magnitude and becomes positive above about 40 at%Co, while h 2 decreases gradually without change in sign.

Magnetic Anisotropy of Pd-Rich Pd–Co, –Ni and –Fe Alloys

The magnetic anisotropy of Pd-rich Pd–Co, –Ni and –Fe alloys has been measured by the torque method. In Pd–Co alloys, the anisotropy constant K 1 at 4.2 K has negative sign, and has a large maximum value of 1.7×10 6 erg/cm 3 at about 10 at%Co. In Pd–Ni alloys, K 1 has positive sign, and decreases monotonically with decreasing Ni content. In contrast to these alloys, K 1 is vanishingly small for Pd–Fe alloys.

Electrical and magnetic properties of YbPdGe and YbPtGe

Electrical resistivity ρ, Hall coefficient RH, thermoelectric power S and magnetization have been measured in the temperature range 4.2 K≤T≤300 K for YbPdGe and YbPtGe. The magnetic resistivity shows Kondo character with −lnT dependence at high temperatures and decreases abruptly according to ferromagnetic ordering below the Curie temperatures of 11.4 K and 4.7 K for YbPdGe and YbPtGe, respectively. The magnetic moments evaluated by extrapolation to T=0 K are 1.0 μB/Yb for both YbPdGe and YbPtGe. The RH shows a shallow minimum at 130 K, increases abruptly with decreasing T and shows a maximum at the Curie temperature for both YbPdGe and YbPtGe. The S has a sharp maximum at about 30 K and a broad minimum at 120 K for both YbPdGe and YbPtGe. The results of ρ and S are compared with those of CePdGe and CePtGe.

Magnetic and electrical properties of the intermetallic compounds R7Rh3 (R=La, Ce, Pr and Nd)

Abstract Magnetic and electrical properties of the hexagonal Th 7 Fe 3 -type R 7 Rh 3 compounds (R=La, Ce, Pr and Nd) have been studied by measuring a.c. magnetic susceptibility, magnetization, electrical resistivity, thermoelectric power and thermal expansion for polycrystalline samples. The Ce 7 Rh 3 and Pr 7 Rh 3 show ferromagnetic ordering below 6.8 and 15.6 K, respectively. In Nd 7 Rh 3 , there are two magnetic ordered phases; the ferromagnetic phase below 11 K and the antiferromagnetic phase up to 32 K. In the antiferromagnetic phase, a metamagnetic transition takes place. Pronounced changes at the magnetic transitions are observed in thermoelectric power.