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 Ni2+xMn1−xGa 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 Ni2+xMn1−xGa single crystals, a reversible strain of ∼ 6% is obtained in fields of ∼ 1 T.

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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 ⌬S m calculated from the magnetization M͑T͒ data measured upon cooling is higher than that estimated from M͑T͒ measured upon heating. Contrary to ⌬S m , the adiabatic temperature change ⌬T ad measured upon cooling is significantly smaller than that measured upon heating. The apparent discrepancy between ⌬S m and ⌬T ad ͑larger ⌬S m , smaller ⌬T ad upon cooling, and smaller ⌬S m , larger ⌬T ad upon heating͒ 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,Sb͒ ferromagnetic shape memory Heusler compounds. The hysteresis causes the magnetocaloric parameters to depend strongly on the temperature and field history of the experimental processes.