Effect of magnetic field on the morphology and fine structure of low-temperature martensite phase in a ferromagnetic [Ni.sub.2.08] [Mn.sub.0.96][Ga.sub.0.96] alloy

The morphology and fine structure of high-temperature austenitic and low-temperature martensitic phases in a ferromagnetic [Ni.sub.2.08][Mn.sub.0.96][Ga.sub.0.96] alloy and the effect of magnetic field on the peculiarities of the martensite formation have been studied. The [Ni.sub.2.08][Mn.sub.0.96][Ga.sub.0.96] alloy in the initial cast and annealed states was found to undergo martensitic and magnetic phase transformations at temperatures [M.sub.s] = 280 K, [M.sub.f] = 265 K, [A.sub.s] = 280 K, [A.sub.f] = 295 K, and [T.sub.C] = 375 K, respectively. Above [M.sub.s], the alloy is in a metastable pre-martensitic state, which leads to a characteristic diffuse scattering and tweed contrast when studying by electron microscopy. An applied magnetic field of up to 600 kA/m was found to affect the martensitic transformation in the alloy. The field application leads to changes in the morphology and fine structure of martensite due to orientation along the field direction of the magnetizations of the energetically advantageous (in terms of the directions of the magnetization vectors) c domains of the existing orientation variants of the martensite crystals having a packet pairwise-twinned morphology. The martensitic structure of the [Ni.sub.2.08][Mn.sub.0.96][Ga.sub.0.96] alloy already formed previously during cooling is not affected by an external magnetic field with a strength of up to 600 kA/m. Keywords: Heusler alloys, thermoelastic martensitic transformation, twinned c domains, magnetic domains, magnetization, magnetic field DOI: 10.1134/S0031918X11050255