Peculiarities of the magnetocaloric properties in Ni-Mn-Sn ferromagnetic shape memory alloys

Magnetocaloric properties of a Ni₅₀Mn₃₆Co₁Sn₁₃ ferromagnetic shape memory alloy have been studied experimentally in the vicinity of a first-order magnetostructural phase-transition low-temperature paramagnetic martensite↔high-temperature ferromagnetic austenite. The magnetic entropy change ΔSₘ calculated from the magnetization $M(T)$ data measured upon cooling is higher than that estimated from $M(T)$ measured upon heating. Contrary to ΔSₘ, the adiabatic temperature change ΔTad measured upon cooling is significantly smaller than that measured upon heating. The apparent discrepancy between ΔSₘ and ΔTad (larger ΔSₘ, smaller ΔTad upon cooling, and smaller ΔSₘ, larger ΔTad upon heating) is caused by the hysteretical behavior of this magnetostructural transition, a feature common for all the alloys in the family of Ni₅₀Mn₂₅₊ₓZ_25-x (Z=In,Sn,Sb) ferromagnetic shape memory Heusler compounds. The hysteresis causes the magnetocaloric parameters to depend strongly on the temperature and field history of the experimental processes.