Martensitic transformation temperature hysteresis narrowing and magnetocaloric effect in ferromagnetic shape memory alloys Ni-Mn-Ga

摘要

The hysteresis narrowing and magnetocaloric effect (MCE) were studied in the Ni-Mn-Ga alloys. Ni_(54)Mn_(24)Ga_(22) and Ni_(51.9)Mn_(27)Ga_(21.1) were selected in order to obtain specific characteristic temperatures of alloys and to study an influence of several factors on the hysteresis width (δ) of basic austenite-martensite (AM) transformation. The effect of martensite crystal lattice softening due to intermartensitic transition (IT) taking place immediately after AM transformation on δ was examined in alloy 1. MCE was measured in alloy 2, in which Curie temperature (T_C) and austenitic start temperature (A_S) coincides. It was demonstrated that the hysteresis width δ reaches about 2 K, if IT is enough close to AM transition. MCE was found to have a maximum at T_C≈A_S.