H. Yasui

Effect of hydrostatic pressure on the magnetic transition temperatures of MnRhAs

The pressure effect on the magnetic transition temperatures of MnRhAs has been measured under pressure up to 15 kbar. The magnetic order-order transition temperature, Tt, and the Curie temperature, Tc, increase with increasing applied pressure and the pressure dependence of T1 and Tc is nonlinear. The pressure derrivatives of the transition temperatures at p = O are obtained to be dTtdp=1.0 degkbar and dTcdp=0.7 degkbar. The transition entropy change at Tt is calculated by means of the thermodynamic equations. The temperature variations of magnetization and susceptibility are also reported. On the basis of these results, the magnetic properties for MnRhAs are discussed.

Magnetic order-order transformation in Mn3Pt

Abstract Mn 3 Pt is an antiferromagnet at T N =485 K, and it transforms to another magnetic structure at T t =400 K. At T t the magnetic moment of Mn changes from 3.3 to 2.2μ B with a lattice volume contraction of 2.25%. From the symmetry of the magnetic structures tetragonal and rhombohedral distortions are expected for the high and low temperature phase, respectively. However, our investigation indicates no deviation from cubic symmetry.

Magnetic excitations in Mn3Pt at high energies by the TOF method

Magnetic excitations in the triangular phase of Mn 3 Pt has been measured mainly in the higher energy region by using a TOF crystal analyser spectrometer. A well defined spin wave branch with a q-linear dispersion has been observed up to 70 meV. The stiffness constant of the dispersion has a very large temperature dependence.

Pressure effect on the Curie temperature and exchange striction of LaMn2Ge2

Abstract The pressure effect on the Curie temperature TC and the thermal expansions of the lattice parameters a and c are studied for the ferromagnetic compound LaMn2Ge2. The pressure derivative of TC is obtained to be dTC/dP = −0.2 K/kbar. Both the exchange strictions of a and c are found to be positive. The relation between the Mn-Mn distance and the Curie temperature is discussed.

Magnons in two magnetic phases of Mn3Pt

Abstract Mn3Pt is an antiferromagnet with a collinear spin structure of TN = 483 K, and it transforms to a triangular structure at Tt=415 K. Spin wave excitations were observed for these magnetic phases, and analyzed by a localized spin model.

Effect of pressure on the Curie temperature of CoCr2O4

Abstract The pressure effect on the Curie temperature T c of CoCr 2 O 4 was measured under pressures up to 11.5 kbar. The pressure derivative of T c is found to be +0.25 K/kbar. On the basis of this result, the relationship between the magnetic transition temperature and volume is discussed.

Field-induced magnetic transitions in intermetallic compound MnRhAs

Abstract The magnetization of MnRhAs is measured under a static magnetic field up to 150 kOe at temperatures from 4.2 to 200 K. Field-induced transitions are observed at temperatures below the transition temperature T t , where the magnetic-order— order transition occurs. From the results, the entropy change at T t is estimated to be ΔS = 0.18 R .

Pressure effect on the Curie temperature and exchange striction of YMn2Ge2

Pressure effect on the Neel temperature (TN) is measured for the antiferromagnetic compound YMn2Ge2 with a ThCr2Si2‐type crystal structure. TN increases linearly with pressure with dTN/dP=23 K/GPa. Thermal expansion of lattice parameters a and c is in the temperature range through TN. Exchange strictions along the a‐ and c‐axis are obtained to be negative and positive, respectively. Volume exchange striction is estimated to be negative. The relation between the lattice parameters and magnetic order is discussed on the basis of the present results.