Relationship between the magnetocaloric effect and sequential magnetic phase transitions in Ni-Mn-Ga alloys

Abstract

The fundamental nature of the magnetic phase transitions in the Ni-Mn-Ga system is investigated quantitatively. By compositional tuning, the first-order metamagnetic/martensitic structural transition (occurring at TM≈200K in the parent compound Ni2MnGa) and the second-order/continuous transition (at TC≈375K in the parent) can be merged. This occurs for Ni55.2Mn18.6Ga26.2, where the entropy changes by ΔSM=−20.4Jkg−1K−1 (in a field of 5T near 317K), at a transition that displays both first- and second-order characteristics simultaneously.