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

Magnetocaloric properties of a ${\text{Ni}}_{50}{\text{Mn}}_{36}{\text{Co}}_{1}{\text{Sn}}_{13}$ ferromagnetic shape memory alloy have been studied experimentally in the vicinity of a first-order magnetostructural phase-transition low-temperature paramagnetic $\text{martensite}\ensuremath{\leftrightarrow}\text{high-temperature}$ ferromagnetic austenite. The magnetic entropy change $\ensuremath{\Delta}{S}_{m}$ calculated from the magnetization $M(T)$ data measured upon cooling is higher than that estimated from $M(T)$ measured upon heating. Contrary to $\ensuremath{\Delta}{S}_{m}$, the adiabatic temperature change $\ensuremath{\Delta}{T}_{ad}$ measured upon cooling is significantly smaller than that measured upon heating. The apparent discrepancy between $\ensuremath{\Delta}{S}_{m}$ and $\ensuremath{\Delta}{T}_{ad}$ (larger $\ensuremath{\Delta}{S}_{m}$, smaller $\ensuremath{\Delta}{T}_{ad}$ upon cooling, and smaller $\ensuremath{\Delta}{S}_{m}$, larger $\ensuremath{\Delta}{T}_{ad}$ upon heating) is caused by the hysteretical behavior of this magnetostructural transition, a feature common for all the alloys in the family of ${\text{Ni}}_{50}{\text{Mn}}_{25+x}{Z}_{25\ensuremath{-}x}$ $(Z=\text{In},\text{Sn},\text{Sb})$ ferromagnetic shape memory Heusler compounds. The hysteresis causes the magnetocaloric parameters to depend strongly on the temperature and field history of the experimental processes.