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 $\text{martensite}\leftrightarrow \text{high-temperature}$ ferromagnetic austenite. The magnetic entropy change $\Delta S_m$ calculated from the magnetization $M\left(T\right)$ data measured upon cooling is higher than that estimated from $M\left(T\right)$ 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 ${\text{Ni}}_{50}{\text{Mn}}_{25+x}{Z}_{25-x}$ $\left(Z=\text{In},\text{Sn},\text{Sb}\right)$ ferromagnetic shape memory Heusler compounds. The hysteresis causes the magnetocaloric parameters to depend strongly on the temperature and field history of the experimental processes.

Figure 1

(Color online) Magnetization curve of ${\text{Ni}}_{50}{\text{Mn}}_{36}{\text{Co}}_1{\text{Sn}}_{13}$ measured during cooling and heating in a magnetic field ${\mu }_{0}H=0.1\text{T}$.

Figure 2

(Color online) Temperature dependence of the magnetization in the vicinity of the martensitic phase transition of ${\text{Ni}}_{50}{\text{Mn}}_{36}{\text{Co}}_1{\text{Sn}}_{13}$ at various magnetic fields.

Figure 3

(Color online) Isothermal magnetic entropy change, $\Delta S_m$, in ${\text{Ni}}_{50}{\text{Mn}}_{36}{\text{Co}}_1{\text{Sn}}_{13}$, calculated from $M\left(T\right)$ measured upon cooling (triangles) and heating (circles).

Figure 4

(Color online) Magnetic field dependence of the adiabatic temperature change in ${\text{Ni}}_{50}{\text{Mn}}_{36}{\text{Co}}_1{\text{Sn}}_{13}$ measured upon heating protocol in the vicinity (a) of the magnetostructural transition and (b) of the Curie temperature of the austenitic phase.

Figure 5

(Color online) Temperature dependence of the adiabatic temperature change, $\Delta T_{ad}$, in ${\text{Ni}}_{50}{\text{Mn}}_{36}{\text{Co}}_1{\text{Sn}}_{13}$ upon cooling (triangles) and heating (circles). Vertical lines denote Curie temperature of the martensitic and austenitic phases, $T_C^M$ and $T_C^A$, respectively, and characteristic temperatures of the direct and reverse martensitic transformations, $T_{AM}$ and $T_{MA}$. Values of $T_C^M$ and $T_C^A$ are taken from Fig. 1. Values of $T_{AM}$ and $T_{MA}$ are extracted from Fig. 2 for the magnetic field ${\mu }_{0}H=2\text{T}$.

Figure 6

(Color online) Magnetic phase diagram of ${\text{Ni}}_{50}{\text{Mn}}_{36}{\text{Co}}_1{\text{Sn}}_{13}$ determined from $M\left(T\right)$ measurements upon heating (full circles) and cooling (empty circles). P denotes paramagnetic martensite, F denotes ferromagnetic austenite. The thick lines show the different processes followed by the system in adiabatic measurements of $\Delta T_{ad}$ (see text). The dashed arrowed line corresponds to one of the isofield measurements represented in Fig. 2. The shadowed areas show the finite width of the phase-transitions bands.