Yoshifuru Mitsui

Thermal Transformation Arrest Phenomena in Mn 2 Sb 0.9 Sn 0.1

Magnetic and structural properties of Sn-substituted Mn2Sb were investigated. A first-order magnetic transition (FOMT) from a ferrimagnetic (FRI) to an antiferromagnetic state occurred between 100 and 200 K, which was accompanied by an iso-structural transformation. Upon cooling in 5 T, the residual FRI phase was observed even at 10 K, and the residual FRI phase slightly decreased with increasing time. The results indicate that the FOMT of Mn2 Sb0.9Sn0.1 is arrested by applying a magnetic field.

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.

Ab initio investigation of Fe substitution effect on magnetostructural transition of CoMnGe

First-principles calculations for the ferromagnetic systems (Co,Fe)MnGe and Co(Mn,Fe)Ge show the hexagonal cell volume decreases as an amount of Fe increases mainly because of the reduction of the lattice constant c. The Fe substitution produces a reduction in the distance between adjacent atoms along the direction of the c axis and an increase in charge density between those atoms. This enhancement of the covalent bond is responsible for the hexagonal-structure stabilization or a decrease of the structural transition temperature from hexagonal to orthorhombic phases.First-principles calculations for the ferromagnetic systems (Co,Fe)MnGe and Co(Mn,Fe)Ge show the hexagonal cell volume decreases as an amount of Fe increases mainly because of the reduction of the lattice constant c. The Fe substitution produces a reduction in the distance between adjacent atoms along the direction of the c axis and an increase in charge density between those atoms. This enhancement of the covalent bond is responsible for the hexagonal-structure stabilization or a decrease of the structural transition temperature from hexagonal to orthorhombic phases.

Cu-substitution effects on the magnetic properties of weak itinerant electron ferromagnet CrAlGe

Cu-substitution effects on ferromagnetism in Cr-base ternary alloy CrAlGe with an orthorhombic TiSi2-type structure was investigated. The lattice parameters of Cr0.95Cu0.05AlGe were a = 4.748 A, b = 8.209 A and c = 8.696 A at room temperature. The spontaneous and effective moment were determined to be ps = 0.533 μB/f.u at 5 K and peff = 1.89 μB/f.u, respectively. The Curie temperature TC was estimated to be 108 K. These ps and TC of Cr0.95Cu0.05AlGe were larger than those of CrAlGe and Ti-substituted compound. The peff/ps was determined to be 3.55, which was smaller than that of CrAlGe and Ti-substituted compound. Obtained results suggest that the substitution of Cu for Cr in CrAlGe leads suppression of its weak itinerant electron ferromagnetism.Cu-substitution effects on ferromagnetism in Cr-base ternary alloy CrAlGe with an orthorhombic TiSi2-type structure was investigated. The lattice parameters of Cr0.95Cu0.05AlGe were a = 4.748 A, b = 8.209 A and c = 8.696 A at room temperature. The spontaneous and effective moment were determined to be ps = 0.533 μB/f.u at 5 K and peff = 1.89 μB/f.u, respectively. The Curie temperature TC was estimated to be 108 K. These ps and TC of Cr0.95Cu0.05AlGe were larger than those of CrAlGe and Ti-substituted compound. The peff/ps was determined to be 3.55, which was smaller than that of CrAlGe and Ti-substituted compound. Obtained results suggest that the substitution of Cu for Cr in CrAlGe leads suppression of its weak itinerant electron ferromagnetism.

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.