Magnetic glassy martensite induced reversible magnetocaloric effect in Heusler alloys

Heusler alloys hold great potential to act as cooling medium for next-generation solid state refrigeration due to their substantial entropy changes at field-driven magnetostructural transitions. One of the key impediments in the use of Heusler alloys for efficient cooling lies in the poor reversibility of magnetocaloric effect (MCE). In this work, a highly reversible MCE with large isothermal heat Q of ∼ 4.83–5.3 kJ/kg near room temperature, is achieved in Ni ₅₀Mn ₃₄In ₁₂Ga ₄ Heusler alloys at the transition between unfrozen canonical spin-glassy martensite and ferromagnetic austenite, crosschecked by indirect and direct methods. Phase field simulations reveal that the presence of spin glass in martensite state can result in reversible field-induced magnetostructural transitions in Heusler alloys, thus effectively circumventing the irreversibility of large MCE at strong first-order transitions without the need of any external stimuli such as mechanical load. The occurrence of such field-induced first-order transitions arose from the negative coupling between magnetic moment and the volume of the material. This work suggests the great power of ferroic glasses in improving the reversibility of promising MCE at first-order phase transitions and may push forward more Heusler alloys close to the practical refrigerant in highly efficient solid-state cooling protocols.