Large magnetocaloric effect near room-temperature by tuning the magneto-structural transition in (Mn, Fe)(Ni, Fe)Si alloy

The observation of near room-temperature coupling of both magnetic and structural transitions in Fe substituted Mn-Ni-Si alloy leads to an interesting magneto-structural transition (MST) phenomenon which intensifies the required magnetocaloric parameters for magnetic cooling applications. The crystal structure analysis reveals that temperature as well as Fe substitution work as the driving forces for deforming the orthorhombic unit cell and to stabilize the hexagonal phase. The correlation between the unit cell parameters of both phases confirms that a large change in unit cell volume (similar to 2.9%) is mainly responsible for the structural transition. The simultaneous substitution of Fe across Ni and Mn sites helps to tune the MST temperature. Both magnetization and calorimetric studies confirm the existence of first-order type structural transition across MST. The [Mn-0.64 Ni-0.64 Fe-0.72 Si] alloy exhibits a large isothermal magnetic entropy change (delta SM) of -19.2 +/- 0.4 J kg(-1) K(-1 )accompanied by a large value of effective refrigerant capacity (RCeffe) of 181.8 +/- 3.7 J kg(-1) due to a magnetic field change of 0-30 kOe. The estimated total entropy change associated with the complete structural transition from the calorimetric studies sets an upper limit for the entropy change of the system. The low cost and non-toxic nature of constituent elements, composition-dependent tunability of the transition temperature, and near room-temperature large magnetocaloric parameters make this alloy potentially suitable to be used as a refrigerant in solid-state magnetic cooling technology.