Preferential reorientation of twin variants in Ni–Mn–Ga single crystal

Abstract

The evidence for the preferential orientation of Ni–Mn–Ga martensitic variants by compression or magnetic field is presented. The evolution of martensitic twinning configuration in Ni 50Mn 27.5Ga 22.5 single crystal was optically observed initially under the applied compressive stress and then followed by the magnetic field. The magnetic field induced strain (MFIS) was measured at different conditions. The MFIS was not observed in the original three-variant self-accommodated state. One percent MFIS was obtained after compression under 5 MPa, attributed to a disappearance of the self-accommodated structure replaced by a two-variant structure. During magnetization, the favorable variants expand at the expense of others. After several cycles of compression and successive magnetization, a near single variant state and MFIS of 5.5% were achieved in the rectangular single crystal. Forty-five degree macroscopic twin bands were observed during the MFIS testing on (0 1 0) surface of an oriented rectangular sample with {1 0 0} faces.