Takejiro Kaneko

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.

Effect of Pressure on Curie Temperature of Calcogenide Spinels CuCr2X4(X=S, Se and Te)

The pressure coefficient of the Curie temperature of CuCr 2 X 4 was obtained from the result of measurement of the variation with pressure in the self inductance of search coil wounded on the specimen vessel. The coefficients, d T c /d p , were founded to be -11.3×10 -4 °Kkg -1 cm 2 for CuCr 2 S 4 , -4.1×10 -4 °Kkg -1 cm 2 for CuCr 2 Se 4 and nearly zero for CuCr 2 Te 4 , respectively. If the main exchange interaction in a pair of Cr ions is thought to be the ferromagnetic superexchange of the Cr-X-Cr type and the antiferromagnetic direct interaction of the Cr-Cr type, it can be seen from the results of the present experiment that the direct Cr-Cr interaction is more sensitive to lattice compression than the superexchange Cr-X-Cr. The magnetic properties of those compounds are also reported.

On the Forced Magnetostriction of Fe-Ni Invar Alloys at 4.2°K

Transverse and longitudinal forced magnetostrictions of Fe-Ni Invar alloys were measured by means of the paper strain gauge technique at room temperature, 77° and 4.2°K. From the measured values of the forced magneto-strictions, the pressure coefficients of the absolute saturation magnetization were estimated. The absolute values of the pressure coefficients of the absolute saturation magnetization were found to decrease monotonically with an increase of Ni concentration. On the basis of Sidorovs theory the pressure effect on the absolute saturation magnetization is discussed.

Effect of Pressure on the Curie Temperature of CrTe and MnSb Compounds of the Nickel Arsenide Type

The effect of the pressure on the Curie temperature of CrTe and MnSb compounds of the nickel arsenide were studied up to a pressure of 4,000 kg/cm 2 . The rate of change of the Curie temperature was -5.5×10 -3 °C kg -1 cm 2 for CrTe and (-3.2±0.5)×10 -3 °C kg -1 cm 2 for MnSb. From the result of the present experiment, the critical pressure and temperature to realize a first kind transition from a ferromagnetic to a paramagnetic state in CrTe are evaluated to be 41,000 kg/cm 2 and 107°K, respectively.

The Change of Curie Temperature of Ordered Au4Mn and of Indium Heusler Alloy by Hydrostatic Pressure

The change of the Curie temperature by the application of 3 katm. of hydrostatic pressure to the indium Heusler alloy as well as the intermetallic compound Au 4 Mn was measured. It was found that the rate of change takes positive values, 1.5×10 -3 and 2.7×10 -3 deg/kg/cm 2 for the Heusler alloy and the Au 4 Mn respectively. It was also elucidated that the relative changes of absolute saturation of magnetization for both alloys are negative, -2.1×10 -12 and -7.2×10 -12 cm 2 /dyne respectively.

Magnetic Structure of Rhombohedral Cr2Se3

Rhombohedral Cr 2 Se 3 is an antiferromagnetic compound with antiferromagnetic AF(L) phase below 38 K (= T t ) and the antiferromagnetic AF(H) one between 38 K and 45 K (= T N ). Neutron diffraction studies for rhombohedral Cr 2 Se 3 are carried out at temperatures from 6 K to 77 K. The results show that the magnetic structures of AF(L) and AF(H) phase are a non-collinear and collinear antiferromagnetic structures, respectively, with the monoclinic magnetic unit cell. It was found that Cr moments at the a-sites are frustrated in the AF(H) phase.

Magnetic Properties of Neodymium Compounds with Va Elements

Magnetic properties of NdP, NdAs and NdSb have been investigated over the temperature range from 4°K to 300°K. The ratio of the susceptibility at the Neel temperature to the one extraporated to 0°K is much larger than 3/2, suggesting that these compounds have large crystal anisotropy. Metamagnetic behaviors were observed at 4.2°K, and the product of the critical field and the susceptibility at the Neel temperature was found to be nearly constant at 7 kOe e.m.u. per mole for all of the compounds. This result can be explained by a simple sublattice model. The value of the saturation magnetization and the large anisotropy are discussed in terms of the admixing of the excited state \(\varUpsilon_{8}\) to the ground state \(\varGamma_{6}\) of Nd 3+ in a cubic crystal field.

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.

Magnetic Properties of CrSb

It is experimentally known that an antiferromagnetic compound CrSb ( T N ≧700 K) with a NiAs type crystal structure exhibits unusual magnetic properties, that is, sharp decrease of magnetic moment, steep increase of magnetic specific heat and of magnetic susceptibility just below T N with increasing temperature. These unusual behaviours are discussed on the basis of a molecular field theory by taking into account anisotropic strain dependence of exchange interactions. And it is pointed out that an effect of anisotropic normal thermal expansion of the crystal lattice can not be neglected.

Pressure Dependence of Magnetic Transition Temperatures and Lattice Parameter in an Antiferromagnetic Ordered Alloy Mn3Pt

The ordered alloy Mn 3 Pt is an antiferromagnet (AF) which shows an AF(D)-AF(F) transition at T C =365 K below the Neel temperature of the F phase T N (F) of 475 K. The pressure dependence of magnetic transition temperatures was studied up to 9.8 kbar. By application of pressure, T N (F) decreases with d T N (F)/d P =-7 K/kbar and T C increases with d T C /d P =14 K/kbar. Above 3.2 kbar, the antiferromagnetic F phase disappears, only the D phase appears and its Neel temperature T N (D) increases with d T N (D)/d P =5 K/kbar with further increase in pressure. The pressure dependence of lattice parameter was measured up to 52 kbar. The volume compressibility was obtained to be 0.9×10 -3 kbar -1 . The magnetic transition temperature vs pressure and lattic parameter phase diagrams were determined.