Abstract
Ferromagnetic Heusler alloys exhibiting martensitic transformations are known to change their shape in an external magnetic field. Magnetization, electric resistance, and specific heat as a function of temperature are examined in ${\mathrm{Ni}}_{54}{\mathrm{Fe}}_{19}{\mathrm{Ga}}_{27}$ single crystal. Structural transition appears as sharp anomaly in these dependencies. This points to an avalanchelike character of martensitic transformation. The jump in resistivity at the structural phase transition and the lower density of states at the Fermi level in the martensite phase supports the hypothesis of the Jahn-Teller origin of the martensitic transformation. Magnetic measurements show that transformation to the martensitic phase is accompanied by the increase of spontaneous magnetization and an increase of magnetocrystalline anisotropy. Magnetization increase is due to different Curie temperatures of austenite and martensite. These were determined from critical behavior using Arrott plot. Additional analysis of magnetic behavior indicates ferrimagnetic ordering in this nonstoichiometric compound. Intrinsic properties of the compound are analyzed with respect to both of the actuation modes possible in magnetic shape-memory alloys. However, neither a magnetically induced martensite transformation nor a magnetically induced reorientation of variants has been observed.
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