Large Magnetic-Field-Induced Strains in Ni-Mn-Ga Alloys due to Redistribution of Martensite Variants

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A polycrystalline and single-crystal samples of near-stoichiometric Ni2MnGa alloys have been investigated. It was confirmed that martensite short crystallographic axis (c-axis) is the easy axis of magnetization. The reversible reorientation of the easy magnetization direction of martensite samples after 5% compression is found. The same reversible reorientation of the easy magnetization direction under applied magnetic field occurs in the single-crystal samples. The field-induced reorientation of the easy magnetization direction is accompanied with more than 4% of sample's dimension change. About the same value of the field-induced strains can be obtained for polycrystalline samples after appropriate thermo-mechanical treatment.