On the origin of giant magnetocaloric effect and thermal hysteresis in multifunctional α-FeRh thin films

We report temperature and field dependent lattice structure, magnetic properties and magnetocaloric effect in epitaxial Fe50Rh50 thin films with (001) texture. Temperature-dependent XRD measurements reveal an irreversible first-order phase transition with 0.66% lattice change upon heating/cooling. First-principle calculation shows a state change of Rh from non-magnetic (0 μB) for antiferromagnetic phase to magnetic (0.93 μB) state for ferromagnetic phase. A jump of magnetization at temperature of 305 K and field more than 5 T indicates a field-assisted magnetic state change of Ru that contributes to the jump. Giant positive magnetic entropy change was confirmed by isothermal magnetization measurements and an in-situ temperature rise of 15 K. The magnetic state change of Rh between antiferromagnetic and ferromagnetic states is the main origin of giant magnetic entropy change and large thermal hysteresis observed.