Magnetocaloric effect in MnNiSi-Fe2 Ge and MnNiSi-Fe-Sn alloys

The near room temperature magnetocaloric effect (MCE) of MnNiSi based alloys is of current interest in magnetocaloric cooling applications [1]. MnNiSi is a ferromagnetic alloy with a Curie temperature (Tc) of 620 K [2], it exhibits a structural transition from orthorhombic to hexagonal above 1200 K [3]. Single element substitution has been found to be unable to decrease Tc to near room temperature, therefore 2 element substitution is necessary to obtain magnetostructural coupling near room temperature[4] [5]. A magnetostructural transition near room temperature is observed in (MnNiSi)1-x Fe 2 Ge $) _{x}(\mathrm{x} = 0.32$ to 0.36) and Mn 0.45 Fe 0.55 NiSi 1-y Sn $_{y}( \mathrm{y} = 0.12$ to 0.18) alloys. A high temperature paramagnetic hexagonal phase which is converted to a low temperature ferromagnetic orthorhombic phase. Fe 2 Ge stabilizes the hexagonal phase of MnNiSi to create a Curie temperature window (CTW) near the room temperature. In Mn 0.45 Fe 0.55 NiSi , it has been observed that the Tc could only be decreased to 438K. The Sn composition was varied from 0.12 to 0.18 to further reduce Tc to near room temperature values. Sn also reduces the cost of the material.