Y. Nakagawa

Magnetization and coercivity of Mn3−δGa alloys with a D022‐type structure

The D022‐type (Al3Ti‐type) phase in the Mn–Ga system is ferrimagnetic; the spin direction is parallel to the tetragonal c axis. The Curie temperature is about 765 K (for δ=0.67), near the decomposition temperature. We have prepared the D022‐type alloys by annealing the quenched ingots of the high‐temperature phase (γMn phase) at 400 or 300 °C for a long time. The preparation becomes much easier if the ingots are powdered by filing before the annealing. The single‐phase specimens of Mn3−δGa were obtained in the composition range 0.15≤δ≤1.06. The coercivity of some specimens was so large that we measured the magnetization curve in high magnetic fields up to 150 kOe. The room‐temperature values of saturation magnetization, remanent magnetization, and coercivity of the powder sample of the alloy with δ=0.67 are 50 emu/g, 25 emu/g, and 13.5 kOe, respectively. We have also studied the effect of magnetic annealing during the transition from the γMn phase to the D022‐type phase and the effect of the addition of F...

Crystal distortion and magnetic structure of γ-Mn(Au) alloys

Abstract γ-Mn alloys containing Au have been examined by magnetic measurements and X-ray and neutron diffraction experiments. The 9 at% Au alloy has a face centered orthorhombic lattice with a = 3.853, b = 3.794 and c = 3.731 A at 11 K, and shows a non-collinear antiferromagnetic structure with 4 sublattices; the three-axis components of the magnetic moments are as follows: μ a = 0, μ b = 1.10 and μ c = 1.91 μ B . A revised phase diagram for γ-Mn(Au) alloy system with 8–16 at% Au is proposed.

Magnetic structure of γ-Mn(Ga) alloys with distorted cubic lattices

Abstract γ-Mn alloys containing Ga undergo a distortion from the face-centered-cubic structure to the face-centered-tetragonal structure with c/a 1, depending on composition. The face-centered-orthorhombic structure also exists in a composition range between the two tetragonal phases. The antiferromagnetic structures of these phases have been determined by neutron-diffraction experiments. The tetragonal and orthorhombic phases exhibit collinear and noncollinear moments, respectively. The results are consistent with the theoretical prediction by Jo et al.

Magnetic properties of hp13 type TiFe6Ge6 alloy

Abstract We have made magnetization measurements, Mossbauer spectroscopy and neutron diffraction on a hexagonal hp13 type TiFe6Ge6 alloy; the 1a and 6i sites are entirely occupied by Ti and Fe, respectively. The alloy exhibits a simple antiferromagnetism with the magnetic moment of about 1 μB/Fe atom at 12 K, the Neel temperature of 510 K and the paramagnetic Curie temperature of 70 K, and the internal field of 162 kOe at 295 K. This is in contrast with complicated magnetic properties of the isotypic alloys such as Fe5Mn2Ge6.

Mictomagnetism of ε ‐MnZn alloys

The e‐MnZn alloy (disordered hcp structure) containing 15 at. % Mn seems to be ferromagnetic below about 200 K; the magnetization σ in a field H of 9.5 kOe amounts to 26 emu/g at a temperature T of 4.2 K. The σ vs T curve in lower H, however, shows a maximum, suggesting mictomagnetism. This is verified by the existence of a hump on the ac susceptibility χac vs T curve. The σ versus concentration curve shows a maximum at 15 at. % Mn. The χac vs T curves for the 12 at. % Mn alloy show a cusp at 45 K in addition to the hump between 80 and 180 K, suggesting a spin glass state. Both the cusp and the hump are suppressed by a dc magnetic field applied parallel to the ac field. The micromagnetic behavior becomes more pronounced for the Mn richer alloys which show only the hump in the χac vs T curve. The σ vs T curves exhibit a magnetic field cooling effect below a freezing temperature Tf. The values of Tf for the alloys containing 20, 30, and 45 at. % Mn are 38, 50, and 75 K, respectively. Although the antiferrom...

Spin-glass-like behavior in the diluted antiferromagnet FexMg1−xTiO3 near the percolation concentration

Abstract Low-field dc magnetization has been measured in the diluted Ising antiferromagnet Fe x Mg 1− x TiO 3 . The sample with 0.13 ≤ x ≤ 0.25 exhibited various properties which are characteristic of spin glass (SG), including the long-time relaxation phenomena of remanent magnetizations. In contrast, samples with x = 0.3 and 0.35 have shown typical reentrant SG-like behavior. By combining the Mossbauer data reported previously, the origin of these kinds of behavior is attributed to the freezing of antiferromagnetic clusters.

Origin of ferrimagnetic ordering in samarium intermetallics

Abstract The ground state of Sm 3+ in the intermetallics with transition metal (M) has been investigated on the basis of the uniaxial crystalline electric field (CEF) and molecular field by taking account of excited J multiplets up to the highest level. When the second order CEF term A 2 0 is negative, with increasing A 4 0 , the Sm magnetic moment initially increases and then suddenly becomes negative, i.e. antiparallel to the M moment. Detailed inspection of the eigenvalues and eigenfunctions has revealed that this sudden reversal of Sm moment is caused by the crossing of energy levels |J = 5 2 , M J = − 5 2 〉 and |J = 5 2 , M J = − 3 2 〉 .

Neutron diffraction study on hp 13 type M7-xMnxGe6 (M = Co, Fe)

Abstract We have made neutron diffraction experiments for Fe 7- x Mn x Ge 6 with x = 2 and 4 and Co 7- x Mn x Ge 6 with x = 3.25, which have the hexagonal hp 13-type structure. It is determined by the Rietvelt analysis for the nuclear reflection that the 1T 1 site is entirely occupied by Mn atoms and the 6T 2 site by Fe or Co atoms and excess Mn atoms. The magnetic reflection of Fe 3 Mn 4 Ge 6 corresponds to the collinear antiferromagnetism with alternating ferromagnetic layers in which the magnetic moments of the 1T 1 and 6T 2 sites are 2.5 and 1.8 μ B /(Mn or Fe) atom, respectively. Magnetic structures of the other alloys are quite complicated.

Magnetic phase transition in ϵ-(Mn1−xFex)3+δGe

Abstract A pseudo-binary system of ϵ-(Mn1−xFex)3+δGe (hexagonal DO19 type structure) has a collinear antiferromagnetic phase in a composition range near x = 0.2 at low temperatures. A field-induced transition from the collinear antiferromagnetic phase to the triangular antiferromagnetic phase (higher temperature phase) was observed in high fields of about 100 kOe.

Magnetic properties of (Mn1−xFex)3+δGe alloys

Abstract We have made X-ray, magnetization and electric resistivity measurements for (Mn 1−x Fe x ) 3+δ Ge with the D0 19 -type structure, and determined the x -dependence of the Neel temperature, the Curie temperature and a transition temperature from the triangular to the collinear magnetic structure for the alloys with δ=0.1 and 0 ⩽ x ⩽0.34. An abrupt change at the transition shows a remarkable thermal hysterisis.