Keiichi Koyama

Magnetic properties of Mn1.9Cu0.1Sb under high pressure

Magnetization measurements were carried out for polycrystalline Mn1.9Cu0.1Sb in magnetic fields up to 5 T in the 10-300 K temperature range under high pressures up to 1 GPa in order to investigate the magnetic properties and the thermal transformation arrest (TTA) phenomenon under high pressures. The spin-reorientation temperature increased from 202 K for 0.1 MPa to 244 K for 1 GPa, whereas the transition temperature from the ferrimagnetic (FRI) to antiferromagnetic (AFM) state did not drastically change at ∼116 K. The magnetic relaxation behavior from the FRI to AFM state was observed in 10 < T ≤ 70 K, which was analyzed using the Kohlrausch-Williams-Watts model. Obtained results indicated that the TTA phenomenon of Mn1.9Cu0.1Sb was suppressed by the application of high pressures.

Magnetization and magnetic phase diagram of Heusler compounds Fe3−y (Mn1−x V x ) y Si (y = 1 and 1.5)

Fe2MnSi exhibits a ferromagnetic transition at TC and another transition to a phase with antiferromagnetic components at a low temperature of TA . By substituting V for Mn, so as to obtain Fe2Mn1−x V x Si, TA decreases with x and then vanishes around x ~ 0.2. In this study, the magnetic transitions are investigated by magnetization measurements for Fe2Mn1−x V x Si (y = 1, 0 ≤ x ≤ 0.2) in high magnetic fields up to ~70 T and for Fe1.5(Mn1−x V x )1.5Si (y = 1.5, 0 ≤ x ≤ 0.1) up to 5 T. For y = 1.5, with increasing x, TC increases and TA decreases as for y = 1, and the rate of the decrease in TA with x is slightly smaller than for y=1. In the low magnetic field region, TA for y = 1 does not significantly change due to the magnetic field but a distinct decrease is observed in high fields. The critical field at 0 K of this transition in Fe2MnSi is found to be larger than 70 T, and with increasing x, the critical field decreases corresponding to the decrease of TA at zero field.

Magnetic and structural properties of MnCo1-xFexGe (0 ≤ x ≤ 0.12)

Structural, magnetic and thermal properties of ferromagnetic MnCo1-xFexGe (0 ≤ x ≤ 0.12) compounds were investigated. The Curie temperature TC and the martensitic transformation temperature TM of MnCoGe (x = 0) were determined to be 340 K and 510 K, respectively. With increasing x from 0 to 0.08, TM decreased and reached room temperature (290 K) for x ∼ 0.08. For x > 0.09, MnCo1-x Fex Ge did not exhibit the martensitic transformation. The compound for x ∼ 0.08 showed a first-order magnetic transition with a thermal hysteresis of 20 K and was accompanied by the martensitic transformation in the vicinity of room temperature. The phase diagram of MnCo1-x Fex Ge (0 ≤ x ≤ 0.12) is presented.

Magnetic field effect on the liquidus boundary of Bi-Mn binary system

The magnetic field effect (MFE) on liquidus boundary of Bi-Mn binary system was investigated by differential thermal analysis (DTA) and the computer coupling of phase diagram method (CALPHAD). The liquidus boundary for Bi-18at.%Mn and Bi-24at.%Mn rose clearly by the application of the magnetic fields. The MFE for liquidus boundary temperature Tliq changed from ΔTliq∝B2 to ΔTliq∝B because of the large increase of the peritectic temperature from BiMn and BiMn1.08 by the application of magnetic field.