Structural and magnetic properties of Ni2MnGa

The martensitic phase transition from a cubic to a tetragonal structure on cooling in the shape-memory ferromagnetic Heusler alloy Ni2MnGa is investigated. The martensitic-transition temperature T-M, known to be 205 K for the nominal composition, was expected to increase with increasing Ni content of the alloy. For the samples Ni2(1+delta)Mn(1+delta)G(1-delta) with delta = 0, 0.046 and 0.10, respectively, the Curie temperature has been determined as 380 K independent of composition. T-M for the sample with delta = 0.046 is also near 205 K, but the sample with delta = 0.10 is single phase and remains tetragonal up to the Curie temperature. The spontaneous polarization of this magnetically uniaxial phase has been determined to be J(s) = 0.16T and an estimate of the magnetocrystalline anisotropy constant is K-1 approximate to 80 kJm(-3).