PUB - Publikationen an der Universität Bielefeld

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 (T-M) toward higher temperature. The observed structural compatibility of the MPT results in a lower thermal hysteresis (Delta T-hyst<5 K at low field). Delta T-hyst remains almost unchanged; however, the field sensitivity of T-M decreases significantly with increasing B content or application of p. As a result, the reversibility of the isothermal entropy change (|Delta S-rev|) 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 (|Delta S-rev| = 21.48 J/kg K for Delta mu H-0 = 5 T), which is comparable to or even larger than the values reported for similar Heusler alloys.