Ferromagnetic shape memory alloys ${\mathrm{Ni}}_{2+x}{\mathrm{Mn}}_{1-x}\mathrm{Ga}$ were studied in the range of compositions $0.16⩽x⩽0.36$. The experimental phase diagram, constructed from differential scanning calorimetry, transport, and magnetic measurements, exhibits distinctive feature in a compositional interval $0.18⩽x⩽0.27$, where martensitic and magnetic transitions merge in a first-order magnetostructural phase transition ferromagnetic $\text{martensite}\leftrightarrow \text{paramagnetic}$ austenite. Observed in this interval of compositions a nonmonotonous behavior of the magnetostructural phase transition temperature was ascribed to the difference in the exchange interactions of martensitic and austenitic phase and to the competition between increasing number of valence electron and progressive dilution of the magnetic subsystem which occur in the presence of a strong magnetoelastic interaction. Based on the experimental phase diagram, the difference between Curie temperature of martensite $T_C^M$ and Curie temperature of austenite $T_C^A$ was estimated. Influence of volume magnetostriction was considered in theoretical modeling in order to account for the existence of the magnetostructural phase transition over a wide range of compositions.

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.

Direct measurements of the magnetocaloric effect in samples of rapidly quenched ribbons of ${\text{Mn}}_{50}{\text{Ni}}_{40}{\text{In}}_{10}$ and ${\text{Ni}}_{50}{\text{Mn}}_{37}{\text{Sn}}_{13}$ Heusler alloys with potential applications in magnetic refrigeration technology are carried out. The measurements were made by a precise method based on the measurement of the oscillation amplitude of the temperature in the sample while is subjected to a modulated magnetic field. In the studied compositions both direct and inverse magnetocaloric effects associated with magnetic (paramagnet-ferromagnet-antiferromagnet) and structural (austenite-martensite) phase transitions are found. Additional inverse magnetocaloric effects of small value are observed around the ferromagnetic transitions.