Field-induced martensitic transformation in new ferromagnetic shape memory compound Mn_1.07Co_0.92Ge

The structural transformation of a ferromagnetic Mn_1.07Co _0.92Ge compound was studied by magnetization measurement in magnetic fields up to 13 T and powder X-ray diffraction measurement in fields up to 5 T. The Curie temperature is determined to be 275 K. At room temperature, the compound has a hexagonal Ni₂In-type structure, and it transforms diffusionlessly into an orthorhombic TiNiSi-type structure at M_S = 210 K with hysteresis. The cell volume expands by 5.3% and the magnetic moment increases by 24% at M_S, accompanied with this martensitic structural transformation. In addition, we confirmed for the first time that magnetic field induces the structural transformation in Mn_1.07Co _0.92Ge at the vicinity of M_S.