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

Magnetocaloric properties of a Ni(50)Mn(36)Co(1)Sn(13) 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 Delta S(m) calculated from the magnetization M(T) data measured upon cooling is higher than that estimated from M(T) measured upon heating. Contrary to Delta S(m), the adiabatic temperature change Delta T(ad) measured upon cooling is significantly smaller than that measured upon heating. The apparent discrepancy between Delta S(m) and Delta T(ad) (larger Delta S(m), smaller Delta T(ad) upon cooling, and smaller Delta S(m), larger Delta T(ad) upon heating) is caused by the hysteretical behavior of this magnetostructural transition, a feature common for all the alloys in the family of Ni(50)Mn(25+x)Z(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.