Structural and magnetocaloric effect studies of Ni43-xTixMn46Sn11 Heusler alloys

Cubic phases of bulk Mn-rich Ni43−xTixMn46Sn11 Heusler alloys (with x = 0, 0.5, 1 and 2) were fabricated by arc melting and their temperature dependent magnetic properties studied. The addition of Ti enhanced the saturation magnetization. The coercive fields and the exchange bias fields increased at lower temperature. The coercive field attains a maximum value at a temperature TMC below which the exchange bias field is higher. The bifurcation between the zero-field cooled and field cooled magnetization curves at low temperatures show evidence of transition from ferromagnetic (FM) to antiferromagnetic (AFM) interactions with large exchange bias fields as large as 496 Oe and 532 Oe for x=0.5and1 alloys respectively at 10 K. The temperature dependence of coercivity appears to switch from noninteracting FM particles to interacting FM and AFM magnetic phases below, TMC, and it is reported here for the first time. A first order magnetic transition occurs for x≤1 as deduced from the thermal hysteresis in the ZFC-FC measurements. We suspect coexistence of martensite and an austenite phases in all alloys, except for x>1 which shows a second order magnetic transition. The austenitic Curie temperature TCA decreased from 282 K to 258 K. The martensitic transition temperature also decreases for x≤1. Peak magnetic entropy changes of 29Jkg−1K−1, 21Jkg−1K−1 and 32Jkg−1K−1 at 5 T were estimated from the magnetic isotherms for x=0, 0.5 and 1 with corresponding refrigerant capacities of 217Jkg−1, 134Jkg−1 and 77Jkg−1 respectively.