On the Instability of the Giant Direct Magnetocaloric Effect in CoMn0.915Fe0.085Ge At. % Metamagnetic Compounds

Abstract

The giant magnetocaloric effect was quantified in CoMn1-xFexGe (x = 0.085-0.12) nom. at. % polycrystals across the high temperature hexagonal (P6(3)/mmc) to low temperature orthorhombic (Pnma) phase transition via differential scanning calorimetry (DSC) and multiple (thermo) magnetization measurements. It was found that increasing Fe content led to the decrease of both the martensitic transformation temperature and entropy change (Delta S) at the point of the phase transition. Moreover, first-time magnetocaloric measurements resulted in irreproducible entropy change versus temperature diagrams, which was attributed to the release of internal pressure in bulk samples that disintegrated into powder upon transformation. CoMn1-xFexGe demonstrated larger magnetic fieldinduced entropy changes and giant magnetocaloric effect (MCE) compared to other CoMn-Ge alloys doped with Si, Sn, Ti, and Ga. However, the observed brittleness and apparent change in volume at the magnetic transition was posited to influence the material's potential for regenerative applications.