Ferromagnetic martensitic transformation and large magnetocaloric effect in Ni35Co15−xFexMn35Ti15 (x = 2, 4, 6, 8) alloys

The crystal structure, ferromagnetic martensitic transformation, and magnetocaloric effect of Ni35Co15−xFexMn35Ti15 (x = 2, 4, 6, 8) alloys have been investigated. All the alloys crystallize in a B2-type cubic structure at room temperature. The Curie temperature of austenite between paramagnetic and ferromagnetic states decreases from 349.0(7) K to 287.2(8) K with increasing Fe content x up to 8, whereas the corresponding martensitic transformation temperature from ferromagnetic austenite to weak-magnetic martensite increases continuously from 182 K to 230 K, and the accompanied thermal hysteresis decreases gradually. The maximum values of magnetic entropy change (ΔSM)/refrigeration capacity reach 9.5(8) J kg−1 K−1/79.4(5) J kg−1 (0–20 kOe) and 24.0(4) J kg−1 K−1/206.8(4) J kg−1 (0–50 kOe), respectively. The present results indicate that the Ni35Co15−xFexMn35Ti15 alloys are considerable for magnetic refrigeration.