The coefficient of refrigeration performance and stress-assisted magnetocaloric effect in meta-magnetic shape memory alloys

Meta-magnetic shape memory alloys (MMSMAs) exhibit multi-physical couplings across a reversible first-order martensitic transition which leads to their potential applications in solid-state refrigeration, thermally or magnetically driven precision actuation, energy harvesting, and magnetic memory storage. Through their magneto-structural transitions and simultaneous transformation latent heat, MMSMAs are capable of the magnetocaloric effect (MCE) at two distinct operating temperatures (i.e. the critical martensitic transformation temperature and the ferromagnetic Curie point of either the austenite or martensite phase). Here, a form of the refrigeration capacity (RC) for MMSMAs is developed from the seminal work of Wood and Potter that exhibits the same assumptions in reversibility as that for simple ferromagnetic coolants. Moreover, the coefficient of refrigeration performance (CRP) is approximated in MMSMAs using a set of 5 commonly measured parameters to compare their MCE potential. Finally, the stress-assisted magnetocaloric effect is described in giant inverse MCE materials, which clearly demonstrates the benefit of stress-induced martensitic transformations and the superelastocaloric effect instead of the giant-inverse MCE through magnetic-field induced transitions.