Magnetostriction of ferromagnetic shape memory alloy Ni2.27Mn0.73Ga studied in magnetic fields up to 10 T

Abstract

Magnetostriction of a non-modulated martensite was measured for Ni2.27Mn0.73Ga ferromagnetic shape memory alloy in steady magnetic fields μ0H up to 10 T at temperatures below room temperature and in μ0H ≤ 1 T at temperatures above room temperature. Linearity of the longitudinal magnetostriction λ|| observed at high fields μ0H > 6 T implies that the magnetostriction is associated with a 3d electron band. The anisotropic magnetostriction obtained in a magnetic field μ0H = 1 T at T = 4.2 K is ∼16 ppm and decreases down to 3 ppm with the increase in temperature. The volume magnetostriction is positive but very small (∼0.6 ppm) under these conditions. In the region of the magnetostructural phase transition the longitudinal and volume magnetostriction showed a complex sigh-changing behavior which depends on the strength of applied magnetic field. Thermal expansion coefficient α of Ni2.27Mn0.73Ga in the martensitic state was measured to be α ∼13 × 10−6 K−1 which is comparable with the thermal expansion coefficient of a non-stoichiometric Ni2.19Mn0.81Ga single crystal.