The giant magnetocaloric effect of optimally prepared Gd5Si2Ge2

The appropriate heat treatment of the Gd5Si2Ge2 alloy prepared from high-purity Gd results in a considerable enhancement of its magnetocaloric effect. The maximum magnetic entropy change increases by ∼80% (from ∼20 to 36 J/kg K) and the adiabatic temperature change increases by ∼55% (from ∼11 to 17 K) for a magnetic field change from 0 to 50 kOe when compared to the as arc-melted material. The magnetic ordering temperature is slightly reduced from ∼277 K in the as arc-melted material to ∼272 K in the fully homogenized and annealed Gd5Si2Ge2. The behavior of the isothermal magnetization as a function of magnetic field changes to some extent, while the heat capacity anomaly at the phase transition temperature is considerably sharper. The 1570 K heat treatment results in the partial ordering and redistribution of the Si and Ge atoms between their corresponding crystallographic sites in the monoclinic Gd5Si2Ge2-type structure and to the removal of the polymorphic orthorhombic Gd5Si2Ge2 phase with the Gd5Si4-type structure, which coexists with the monoclinic phase in the as arc-melted alloy.