On the instability of the giant direct magnetocaloric effect in CoMn 0.915 Fe 0.085 Ge at. % metamagnetic compounds.

The giant magnetocaloric effect was quantified in CoMn1-x Fex Ge (x = 0.085-0.12) nom. at. % polycrystals across the high temperature hexagonal (P63 /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 ([Formula: see text]) 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-x Fex Ge demonstrated larger magnetic field-induced entropy changes and giant magnetocaloric effect (MCE) compared to other CoMnGe 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.