Complete and reversible magnetostructural transition driven by low magnetic field in multiferroic NiCoMnIn alloys

Magnetic-field-induced first-order magnetostructural transition (MFI-FOMST) brings about an ample variety of intriguing magnetoresponsive effects including magnetocaloric effect, magnetoresistance and magnetostrain. Metamagnetic shape memory alloys (MSMAs) exhibit MFI-FOMST and thus giant magnetoresponsive effects, but the critical field for complete and reversible MFI-FOMST, (μ₀∆H)_min, is too high (usually >5 T), which has been a longstanding bottleneck for practical applications. Here, we successfully achieved complete and reversible MFI-FOMST under a low field of 1.5 T, which can be generated by permanent magnets, in a prototype MSMA. The significant reduction of (μ₀∆H)_min is realized by simultaneously enlarging the distance between Curie transition and magnetostructural transition and manipulating the geometric compatibility between the transforming phases. The low (μ₀∆H)_min provides a great opportunity for attaining low-field-induced large reversible magnetoresponsive effects. For instance, a large reversible magnetocaloric effect is achieved under 1.5 T. Our realization of low-field-induced complete and reversible first-order magnetostructural transition may push a significant step forward towards the practical use of MSMAs. This work is instructive for developing novel magnetic materials with low-field-actuated first-order phase transition for applications as magnetic actuators, magnetoresistors and solid-state refrigerants.