The influence of hydrostatic pressure and annealing conditions on the magnetostructural transitions in MnCoGe

Abstract

In this work, the phase transitions of stoichiometric MnCoGe alloys were studied by systematically varying the annealing conditions and applying hydrostatic pressure. First-order martensitic structural transitions from the Ni 2In-type hexagonal austenite phase to the TiNiSi-type orthorhombic martensite phase spanned a wide temperature window (> - > 200 K) as a result of quenching the samples at temperatures ranging from the solid phase at 700 ° C to the liquid phase at 1150 ° C. Despite the large variation in their structural transition temperatures, the changes in cell parameters across the structural transitions and the Curie-Weiss temperatures of the martensite/austenite phase were relatively small. For the sample quenched from 800 ° C, coupled magnetostructural transitions were observed, and the largest maximum magnetic entropy change was found to be - Δ S m a x = 33.6 J/kg K for a 7-T field change. The coupled magnetostructural transitions and the corresponding magnetic entropy enhancements were found to also be achievable by applying hydrostatic pressures. Meanwhile, as the quenching temperatures or hydrostatic pressures increased, the first-order martensitic structural transition shifted toward lower temperature until it was ultimately absent, in which case only the crystal structure and magnetic transition of the Ni 2In-type hexagonal austenite phase were present.