Satoshi Akamaru

Magnetic Phase Diagram of Ce(Ni1-xPdx)2Ge2.

We have measured the temperature dependence of the magnetic susceptibility, the electrical resistivity, the specific heat and the Hall coefficient on the pseudo-binary series Ce(Ni 1- x Pd x ) 2 Ge 2 (1.0≥ x ≥0.0). The Neel temperature decreases monotonously from 5.1 K for CePd 2 Ge 2 to 2.8 K for Ce(Ni 0.8 Pd 0.2 ) 2 Ge 2 with decreasing Pd concentration. For x ≤0.1, the ground state is paramagnetic.

In situ measurement of alternating current magnetic susceptibility of Pd–hydrogen system for determination of hydrogen concentration in bulk

An alternating current magnetic susceptometer for use as a hydrogen gauge for hydrogen-storage materials was designed and developed. The experimental system can simultaneously measure the hydrogen equilibrium pressure and the magnetic susceptibility of metal hydrides. The background voltage of the susceptometer was stabilized for a long period of time, without any adjustments, by attaching an efficient compensation circuit. The performance of the susceptometer at a static hydrogen concentration was demonstrated by measuring the magnetic susceptibility of a Pd-hydrogen system under equilibrium conditions. The in situ measurement of the magnetic susceptibility of Pd during hydrogen absorption was carried out using the susceptometer. Since the in situ magnetic susceptibility obtained at a lower initial hydrogen pressure agreed with the magnetic susceptibility measured at a static hydrogen concentration, the susceptometer could be used to determine the hydrogen concentration in Pd in situ. At a higher initial hydrogen pressure, enhancement of the magnetic susceptibility was observed at the beginning of hydrogen absorption because the magnetic moments induced by the large temporary strain generated in the Pd affected the magnetic susceptibility.

Preparation of Ni Nanoparticles on Submicron-Sized Al2O3 Powdery Substrate by Polyhedral-Barrel-Sputtering Technique and Their Magnetic Properties

Ni nanoparticles were prepared on a submicron-sized Al2O3 powdery substrate by the polyhedral-barrel-sputtering technique and their microstructure and magnetic properties were investigated. By this technique, nanoparticles with an average diameter of 3.9–7.9 nm were prepared on the Al2O3 particles surface, and the size distribution of the nanoparticles was reproduced using a log-normal formula. The deposited Ni nanoparticles were composed of a NiO layer, which was formed by air oxidation, and a Ni core. The magnetization curves suggested that the all the prepared samples exhibited superparamagnetic behavior, which can be explained by considering the size distribution of the Ni nanoparticles. An exchange-bias effect, which arising from the core–shell structure, was also observed. From the saturated magnetic moments of the Ni core, the thickness of the surface layer was estimated to be 1.0–1.3 nm, which was comparable with that of passivated oxide layer of bulk Ni.

Magnetic Properties and de Haas-van Alphen Effect of PrNi2Al5

We have succeeded in growing a high-quality single crystal of PrNi 2 Al 5 , and have measured the electrical resistivity, magnetic susceptibility, magnetization and specific heat. Any magnetic phas...

de Haas-van Alphen effect and Fermi surfaces of LaNi2Al5

Magnetoresistance and de Haas-van Alphen measurements have been performed to investigate the Fermi-surface property of LaNi 2 Al 5 , which is a reference material of the magnetic dense-Kondo compound CeNi 2 Al 5 . Thirteen branches with the frequencies from 1.25 ×10 6 to 101 × 10 6 Oe have been observed in the angular-resolved dHvA measurements, and the magnetoresistance shows the existence of open orbits. The results are well explained by the Fermi surfaces obtained from an FLAPW band-structure calculation.

Magnetism and Electronic Structure Calculations of Pd-TM Alloys and Hydrogen Systems

The electronic and magnetic properties of Pd-TM (Fe, Co, and, Ni) alloys and their hydrides have been studied using first-principles calculations by Korringa-Kohn-Rostoke Coherent potential approximation (KKR-CPA) Green’s function method with density functional theory (DFT). The nature and the concentrations of the alloying elements and hydrogen have been examined. In addition, the magnetic properties associated with the density of states and the Fermi level in Pd-TM alloys and their hydrides are discussed. In particular, we find that the minority spin density of nickel (3d) has a sharp peak near the Fermi level. In the case of Fe and Co, the sharp peak exists above the Fermi level and this difference affects the spin polarization.