First-order magnetostructural transformation in Fe doped Mn-Co-Ge alloys

Substitution of Fe for Mn atoms in Mn-Co-Ge alloys was employed for tailoring concurrent structural and magnetic phase transitions. First-order magnetostructural transition from paramagnetic hexagonal Ni₂In-type parent phase to ferromagnetic orthorhombic TiNiSi-type martensite was achieved. A giant magnetocaloric effect of AS_m = -9.74 J kg¹ K ¹ was obtained under magnetic field change of 5 T in the vicinity of phase transition temperature. This result indicates that Fe doped Mn-Co-Ge alloys are ideal candidates for magnetic refrigeration applications. Furthermore, the magnetic field-induced martensitic transformation, associated with a large lattice strain of ∼12%, was directly evidenced by in situ synchrotron high-energy X-ray diffraction.