Field-sensitivity and reversibility of the inverse magnetocaloric effect at martensitic transformations

The magnetic field-sensitivity of martensitic phase transitions (MPTs) responsible for magnetocaloric effects has been examined in B-substituted Ni50Mn34.8In15.2−xBx Heusler alloys (x = 1, 2, 3, and 4). Increasing boron substitution acts as a positive chemical pressure similar to the effect of hydrostatic pressure (p) and shifts the martensitic phase transition temperature (TM) toward higher temperature. The observed structural compatibility of the MPT results in a lower thermal hysteresis (ΔThyst<5 K at low field). ΔThyst remains almost unchanged; however, the field sensitivity of TM decreases significantly with increasing B content or application of p. As a result, the reversibility of the isothermal entropy change (|ΔSrev|) reduces for higher B concentration or under hydrostatic pressure p. The experimental observation reveals that the lower field-sensitivity of the MPT with increasing B or p is associated with the simultaneous increase in the magnetocrystalline anisotropy energy (MAE) and decrease in the Zeeman energy (ZE). The relatively larger ZE and smaller MAE for x = 1 result in the improved reversibility of the entropy change (|ΔSrev| = 21.48 J/kg K for Δμ0H = 5 T), which is comparable to or even larger than the values reported for similar Heusler alloys.