The Heusler-type alloy ${\mathrm{Ni}}_{2+x}{\mathrm{Mn}}_{1-x}\mathrm{Ga}$ exhibits well defined shape memory properties in a ferromagnetic state, which means that the martensitic transition temperature is lower than the Curie point of this material. The change of composition makes these characteristic temperatures approach each other. To study this behavior, the measurements of specific heat, ac magnetic susceptibility, and dc resistivity were performed. The phase diagram of the cubic ferromagnet describing possible structural and magnetic transitions is obtained theoretically. This diagram is compared with experimental data on ${\mathrm{Ni}}_{2+x}{\mathrm{Mn}}_{1-x}\mathrm{Ga}.$ An estimate is given of the magnetic-field influence on the temperature of martensitic transformation in the studied alloys.

In ferromagnetic alloys with shape memory large reversible strains can be obtained by rearranging the martensitic domain structure by a magnetic field. Magnetization through displacement of domain walls is possible in the presence of high magnetocrystalline anisotropy, when martensitic structure rearrangement is energetically favorable compared to the reorientation of magnetic moments. In ferromagnetic Heusler alloys Ni$_{2+x}$Mn$_{1-x}$Ga the Curie temperature exceeds the martensitic transformation temperature. The fact that these two temperatures are close to room temperature offers the possibility of magnetically controlling the shape and size of ferromagnets in the martensitic state. In Ni$_{2+x}$Mn$_{1-x}$Ga single crystals, a reversible strain of $\sim 6$% is obtained in fields of $\sim 1$ T.Comment: review on ferromagnetic shape memory alloys (FSMAs

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.

A systematic study of magnetic properties of ${\mathrm{Ni}}_{2+x}{\mathrm{Mn}}_{1-x}\mathrm{Ga}$ $(0⩽x⩽0.19)$ Heusler alloys undergoing structural martensite-austenite transformations while in the ferromagnetic state has been performed. From measurements of spontaneous magnetization, $M_s\left(T\right)$, jumps $\Delta M$ at structural phase transitions were determined. Virtual Curie temperatures of martensite were estimated from the comparison of magnetization in martensitic and austenitic phases. Both saturation magnetic moments in the ferromagnetic state and effective magnetic moments in paramagnetic state of Mn and Ni atoms were estimated and the influence of delocalization effects on magnetism in these alloys was discussed. The experimental results obtained show that the shift of martensitic transition temperature depends weakly on composition. The values of this shift are in good correspondence with the Clapeyron-Clausius formalism taking into account the experimental data on latent heat at martensite-austenite transformations.

Structural and magnetic properties of a ${\text{Ni}}_{50}{\text{Mn}}_{34.8}{\text{In}}_{15.2}$ ferromagnetic shape memory alloy doped by ${}^{57}\text{F}\text{e}$ at the Mn sites have been studied by x-ray diffraction, Mössbauer spectroscopy and superconducting quantum interference device magnetometry. Obtained experimental results have disclosed unique magnetostructural transition from a high-temperature ferromagnetic austenitic phase to a low-temperature paramagnetic martensitic phase at $M_f=290\text{K}$. Complex magnetic ordering which can be classified as a cluster glass state is formed in ${\text{Ni}}_{50}{\text{Mn}}_{34.3}{{}^{57}\text{F}\text{e}}_{0.5}{\text{In}}_{15.2}$ on further cooling below $T_C^M=162\text{K}$. The abnormal magnetostructural transition observed in ${\text{Ni}}_{50}{\text{Mn}}_{34.3}{{}^{57}\text{F}\text{e}}_{0.5}{\text{In}}_{15.2}$ is suggested to originate from the weakening of exchange interactions due to an abrupt change in Mn-Mn interatomic distances occurring upon the martensitic transformation.