First-Order Phase Transition at the Curie Temperature in MnAs and MnAs_<0.9>Sb_<0.1>(Condensed matter: structure and mechanical and thermal properties)

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Structural transformations of MnAs and MnAs_<0.9>Sb_<0.1> were investigated by X-ray diffraction in high magnetic fields up to 5T. The temperature dependence of the magnetization was measured in a magnetic field of 0.01T and the Curie temperature T_C was determined to be 315K for MnAs and 290K for MnAs_<0.9>Sb_<0.1> during heating process. For both compounds, a metamagnetic transition from a paramagnetic to a ferromagnetic state was observed above T_C. The X-ray diffraction profile at 319K for MnAs showed a single phase of an orthorhombic MnP-type structure in zero field. An applied magnetic field of 3T induced the appearance of a hexagonal NiAs-type structure. On further increase of the magnetic field, a single phase with a hexagonal structure was realized above 3.5T in a forced-ferromagnetic state. The X-ray diffraction profile at 295K for MnAs_<0.9>Sb_<0.1> showed a hexagonal NiAstype structure. The coexistence of ferromagnetic and paramagnetic states with different lattice parameters was confirmed in a magnetic field of 2.5T. The volume expansion induced by a magnetic field was found to be 2.1% for MnAs and 1.1% for MnAs_<0.9>Sb_<0.1>.
社団法人日本物理学会の論文
2006-08-15