Izuru Umehara

Magnetic and electrical properties of U-Ge intermetallic compounds

We have clarified the magnetic and electrical properties of U 7 Ge, U 5 Ge 3 , U 3 Ge 4 and UGe 2 , measuring the electrical resistivity, thermoelectric power, Hall coefficient, magnetic susceptibility, magnetization and specific heat. U 7 Ge and U 5 Ge 3 , which are Pauli paramagnetic compounds, become superconductive below 1.40 K and 0.99 K, respectively. The latter compounds U 3 Ge 4 and UGe 2 indicate ferromagnetism. Anisotropic properties of UGe 2 are well reflected in the electrical resistivity, magnetic susceptibility and magnetization.

Comment on the de Haas-van Alphen Effect in the Superconducting Mixed State of 2H–NbSe 2

We present the de Haas-van Alphen (dHvA) effect in the superconducting mixed state of 2H–NbSe 2 . Our data are consistent with the dHvA results obtained by Graebner and Robbins, which have been the subject of controversy from the viewpoint of experiment and theory. We discuss the reason why the theoretically expected cylindrical Fermi surfaces are not detected in the dHvA experiment and also the mechanism of the dHvA effect in the mixed state.

Magnetoresistance and de Haas-van Alphen Effect in UB12

We have measured the magnetoresistance and de Haas-van Alphen (dHvA) effect in UB 12 . Shown by the result of magnetoresistance, this material is a compensated metal, and possesses an open orbit along the direction. The detected dHvA branches are roughly explained by the recent band calculation performed by Harima et al . The cyclotron mass is in the range of 0.6 m 0 to 6 m 0 .

Detection of Ni magnetic moment in GdNi2 compound by magnetic Compton profile (MCP) method

The Ni magnetic moment in the GdNi2 Laves phase compound is studied in detail by the use of the magnetic Compton profile (MCP) method. Analysis of the MCP, measured at 30 K, reveals that the spin component of Ni 3d electrons coupled antiparallel to that of Gd 4f electrons, and it was confirmed that the Ni retains a spin magnetic moment of 0.16 ± 0.08 μB. Furthermore, the total magnetic moment, including the angular momentum component, is found to be 0.23 ± 0.11 μB and this value that is obtained is in accord with that derived from direct measurement of the bulk magnetization. Our finding of the existence of the Ni magnetic moment contradicts the well-known fact that Ni loses its magnetic moment in the Laves phase of rare-earth (RE)–Ni compounds. In addition, the magnetic moment originating from the electrons with s- and p-character, which are donated by the Gd and Ni atoms, is also observed and quantified.

High Field Magnetoresistance and de Haas-van Alphen Effect in CeNi

We have measured the magnetoresistance and de Haas-van Alphen (dHvA) effect in CeNi in the field up to 150 kOe and at temperature down to 0.4 K. This material is found to be a compensated metal with equal carrier concentration of electrons and holes. The open orbits exist along the b - and c -axes. Four dHvA branches have been found in the field along the b -axis. The dHvA frequencies and the cyclotron masses are 3.60 ×10 7 Oe (10.3 m 0 ), 1.25 ×10 7 Oe (8.91 m 0 ), 6.58 ×10 6 Oe (3.05 m 0 ) and 2.15 ×10 6 Oe (2.58 m 0 ).

Magnetoresistance and de Haas-van Alphen Effect in UC

We have measured the magnetoresistance and de Haas-van Alphen oscillation of UC. The Fermi surface of semimetal UC is found to consist of three hole-ellipsoids located at the X points and six electron-ellipsoids at the W points in the fcc Brillouin zone. The cyclotron mass of electron at the direction is 2.67 m 0 , which is heavy compared to that of hole, 0.84 m 0 .

The development of a high pressure micro-cell for magnetization and specific heat measurements: the effect of pressure on the magnetism in CeAg

A micro-pressure cell has been developed for measurements of specific heat and magnetization by using a commercial SQUID magnetometer. This small piston-cylinder device can be used up to 2 GPa. In this paper, we report on the efficiency of our micro-cell and present some results of the pressure effect on the magnetic and thermal properties of CeAg.

Hydrostatic pressure effect on magnetic phase transition and magnetocaloric effect of metamagnetic TmZn compound

The magnetocaloric effect (MCE) is an intrinsic thermal response of all magnetic solids which has a direct and strong correlation with the corresponding magnetic phase transition. It has been well recognized that the magnetic phase transition can be tuned by adjusting applied pressure. Therefore, we perform the high hydrostatic pressure magnetization measurements (up to 1.4 GPa) on a recently reported giant MCE material of TmZn. The results indicate that the Curie temperature of TC increases from 8.4 K at the ambient pressure to 11.5 K under the pressure of 1.4 GPa. The field-induced first order metamagnetic transition is getting weak with increasing pressure, which results in a reduction of MCE. The hydrostatic pressure effect on the magnetic phase transition and MCE in the metamagnetic TmZn is discussed.

Fermi surface property of branch d in CeIn3

Abstract We have measured the de Haas-van Alphen effect of the heavy-electron compound CeIn 3 . The Fermi surface and the cyclotron mass of branch d are discussed.

Magnetoresistance and de Haas-van Alphen Effect in the Antiferromagnetic Compound NdIn 3

We have measured the magnetoresistance and de Haas-van Alphen (dHvA) effect in both the antiferromagnetic and paramagnetic states of NdIn 3 . Many dHvA branches are detected in the dHvA experiments. Among them, a nearly spherical Fermi surface in the paramagnetic state, which corresponds to a band 7-electron Fermi surface of the non-4 f reference compound LaIn 3 , is changed in the antiferromagnetic state into a multiply connected Fermi surface with necks. The cyclotron masses of NdIn 3 are in the range of 0.30 m 0 to 1.05 m 0 , which are twice as large as those of LaIn 3 .