The impact of hydrostatic pressure and uniaxial strain on the of Ni-Co-Mn-Sb Heusler alloy involving 4 O martensite

Ni-Co-Mn-Sb ferromagnetic shape memory alloys have promise for application in solid-state magnetic refrigeration, but the narrow working temperature region hinders their application. Here, we use ab initio calculations to explore the influence of hydrostatic pressure and uniaxial strain on the working temperature range. More importantly, the modulated martensite phase with an orthorhombic four-layered structure (4 O), which is closely related to the functional properties, is considered systematically. The results show that hydrostatic pressure can widen the working temperature region to a high temperature. The working temperature range of modulated martensite is increased by 35 K/GPa and that of non-modulated martensite is 40 K/GPa. Compared to hydrostatic pressure, uniaxial strain can widen the working temperature range not only to a high temperature but also to a low temperature. For every 0.25% compression or tension strain, the working temperature range of modulated martensite is changed by 15 K to high-temperature or low-temperature respectively. The same trend is also observed in non-modulated martensite, but the widened temperature range is 13 K. The nature of the variation in the working temperature range can be traced back to the change in electronic structure. Moreover, both methods can keep the system with a large magnetic moment difference while widening the working temperature range. These results illuminate hydrostatic pressure and uniaxial strain are effective ways to widen the working temperature range.