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

The hysteresis narrowing and magnetocaloric effect (MCE) were studied in the Ni–Mn–Ga alloys. Ni54Mn24Ga22 and Ni51.9Mn27Ga21.1 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 (TC) and austenitic start temperature (AS) 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 TC≈AS.