Takeshi Kanomata

Pressure effect on the magnetic transition temperatures in the intermetallic compounds Mn3MC (M=Ga, Zn and Sn)

The pressure effect on the magnetic transition temperatures of Mn 3 GaC, Mn 3 ZnC and Mn 3 SnC were measured under pressures up to 13 kbar. The pressure derivatives of the transition temperatures are obtained to be d T t /d P =-3.5 K/kbar and d T C /d P =0.4 K/kbar for Mn 3 GaC, d T t /d P =-0.9 K/kbar and T C /d P =0 for Mn 3 ZnC and d T C /d P =-1.9 K/kbar for Mn 3 SnC, where T t and T C are the magnetic order-order transition temperature and the Curie temperature, respectively. An intermediate magnetic phase (I) is induced in Mn 3 GaC under pressures above 3 kbar. The triple point (Antiferro./I/Ferro.) was determined to be T c =158 K and P c =3 kbar. The temperature variations of magnetization, magnetic susceptibility and latlice parameter were also measured.

Precise Magnetization Measurements of Single-Crystalline FeSi under High Pressure

Magnetization process and susceptibility measurements at high pressures up to P =12 kbar have been performed on single-crystalline FeSi in the temperature range from T =5 K to 300 K using a SQUID magnetometer with a miniature high-pressure clamp cell. From the analyses of these data, the volume dependence of the susceptibility χ for T =300 K is estimated to be d ln χ/ d ln V =10.3. Using an exchange enhanced semiconductor model, the energy gap for T =0 K, E g 0 , and the volume dependence of E g 0 , d ln E g 0 / d ln V , are evaluated to be 62 meV for P =0 kbar and -10.8, respectively.

Magnetic Behavior of Mn3GaC under High Magnetic Field and High Pressure

We have measured the magnetization and magnetostriction of Mn 3 GaC in pulsed high magnetic fields up to 37 T and the magnetization under steady magnetic field and pressure up to 0.82 GPa. Mn 3 GaC is antiferromagnetic (AF) at low temperatures. It exhibits successive transitions to an intermediate (I), to a ferromagnetic (F) and to a paramagnetic phase. The transition between the AF and I phases is first order and the others are second order. The transition temperature between the I and F phases does not change greatly with increasing magnetic field. At low temperatures, a metamagnetic transition from the AF to the I state is observed. Volume magnetostriction measurement at 4.2 K indicates that the volume is abruptly decreased by the metamagnetic transition and then gradually shrinks with increasing field. High pressure stabilizes the F phase and enhances the Mn moment.

Cooling-induced shape memory effect and inverse temperature dependence of superelastic stress in Co2Cr(Ga,Si) ferromagnetic Heusler alloys

Normally, shape memory effect (SME) is obtained by the reverse martensitic transformation, therefore only induced by heating a sample from the deformed martensite phase. In this study, we report a phenomenon of cooling-induced SME, observed in a Co2Cr(Ga,Si) Heusler alloy, where the normal heating-induced SME can be obtained at the same time. The cooling-induced SME is attributed to an abnormal martensitic transformation in Co2Cr(Ga,Si) Heusler alloy. Moreover, an inverse temperature dependence of superelastic stress was also observed. The discoveries of these phenomena provide application possibilities for shape memory alloys, especially at low temperatures.

Transport Properties of Ternary Magnetic Compounds Mn3-xMxGaC (M=Cr and Fe)

The electrical resistivities (ρ) and the thermoelectric powers (S) of Mn2.95Fe0.05GaC and Mn2.95Cr0.05GaC are studied to investigate the mechanism of the antiferromagnetic (AF)-ferromagnetic (F) transitions. The substitution of Fe or Cr for Mn decreases and increases the first order transition temperature, respectively. The experimental results suggest that the magnetic transitions of Mn2.95Fe0.05GaC and Mn2.95Cr0.05GaC should be discussed in terms of itinerant magnetism.

Pressure Induced Magnetic Transition of Mn3Ga1-xAlxC

We have measured the magnetization of Mn 3 Ga 1- x Al x C with x =0, 0.01 and 0.02 under pressure up to 1.25 GPa. A magnetic transition from an antiferromagnetic (AFM) to an intermediate (IM) state with spontaneous magnetization is observed under pressure. We have determined the phase diagram in the pressure-temperature plane. The application of pressure increases the magnetization in the ferromagnetic (FM) phase for all these compounds. We have also measured the thermal expansion of Mn 3 Ga 0.97 Al 0.03 C. It is consistent with the pressure effects on the magnetization and suggests the magnetic contribution to the thermal expansion as ω m FM < ω m IM < ω m AFM . Neutron diffraction experiments were performed on Mn 3 Ga 0.95 Al 0.05 C. Bragg peaks corresponding to an antiferromagnetic component were observed in the IM state. It is highly possible that the IM state has a canted ferromagnetic structure.

Magnetic properties of intermetallic compound La0.3Y0.7Mn2Ge2

Intermetallic compound La 0.3 Y 0.7 Mn 2 Ge 2 with the ThCr 2 Si 2 -type structure is antiferromagnetic (AF) below T t =170 K and ferromagnetic (F) between T t and T c = 340 K. Field-induced AF-F transitions are observed at temperatures below 170 K. The measurements of pressure effect on magnetic transition temperatures show that T c decreases and T 1 increases with pressure and the F phase disappears at pressures above 8 kbar

Exchange Strictions of Calcogen Spinels CuCr2X4 (X=S, Se and Te)

The temperature dependence of the lattice constants of CuCr 2 X 4 (X=S, Se and Te) was determined in a temperature range from 100 to 700 K by an X-ray diffraction technique. The specific heat of CuCr 2 Se 4 was also measured. The temperature dependence of the exchange strictions of CuCr 2 X 4 (X=S, Se and Te) was estimated from these results. Based on the molecular field theory proposed by Bean and Radbell, we estimated the pressure coefficients of the Curie temperature to be -1.1×10 -3 , -0.4×10 -3 and 0 deg. cm 2 /kg for CuCr 2 S 4 , CuCr 2 Se 4 and CuCr 2 Te 4 , respectively, which were in agreement with the values obtained by direct measurements.

Photoemission and Absorption Spectroscopy of Mn2Sb, MnAlGe, Mn2As, Cr2As and Fe2As

Electronic structures of ferri-, ferro- and antiferromagnetic Cu 2 Sb type intermetallic compounds have been studied by ultraviolet and X-ray photoemission spectroscopy (UPS, XPS) as well as by X-ray absorption spectroscopy (XAS). The different spectral features in the core level XPS and the 2p XAS spectra of these materials are discussed by considering the non-equivalent sites of the transition metal atom, M(I) and M(II). The valence band photoemission spectra are also discussed in comparison with the results of recent band calculations.

Pressure Effect of the Lattice Parameters for Mn2Sb and MnMGe (M=Al, Ga)

High-pressure powder X-ray diffraction experiments have been performed for Mn2Sb, MnAlGe and MnGaGe up to a pressure of 7.7 GPa at 300 K. Mn2Sb exhibits a discontinuous change in the lattice parameters a and c at about 3.5 GPa with increasing pressure. For MnAlGe and MnGaGe, the lattice parameters decrease linearly with increasing pressure.