Kniazkyi V. The theory of the thermoelastic and magnetic properties of the single crystals and films of the Ni-Mn-Ga alloys

A superelasticity of the axially compressed single crystals of thermoelastic Ni-Mn-Ga martensites has been studied in the framework of Landau theory with two-component order parameter.The values of the coefficients of Landau expansion, the temperature dependencies of the martensitic transformation strain, and the stiffness coefficients have been computed for two Ni-Mn-Ga alloy specimens. A thickness dependence of martensitic transformation temperature has been studied for the submicron Ni-Mn-Ga films sputter deposited and annealed on the ceramic substrate. A theoretical approach to the description of this film has been developed in the dissertation thesis and used then for the computation of the magnetization loops and initial magnetic susceptibility. A consistent procedure is elaborated for the quantitative determination of the angle between the easy-magnetic axis and the film normal and for the estimation of the ratio between the magnetic anisotropy energy and the magnetostatic energy.