MnGa合金の磁性

概要

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Magntic properties of ferromagnetic MnGa alloys with CuAul type (δ-phase) and cubic γ-brass type (ζ-phase) have been investigated by magnetization and neutron diffraction measurements. The δ-phase stable in low temperature has a ferrimagnetic structure with spins along the c-axis, where spins of the excess Mn atom occupying the Ga site couple antiparallel to that of the regular Mn site. The magnetic moment determined at 4.2K is 2.5μ_B/Mn for the regular site and 3.8μ_B/Mn for the excess one. The ζ-phase which is stable in high temperature has been believed to be a simple ferromagnet, however, by neutron diffraction super lattice reflections with indices like (1/2,1/2,1/2) were observed, indicating antiferromagnetic coupling of Mn moments with a unit cell doubling the a, b and c-axes. The magnetic moments participating this spin structure have a direction perpendicular to the [111] direction. Detailed spin structure has not been determined due to uncertain factors of the crystal structure.