An exploration on magneto-shape memory effect in a Co-Ni single crystal

Abstract
A Co-33%Ni (in mass) single crystal was grown by floating zone method in argon gas. The intrinsic magnetic properties, martensitic and austenitic transformation temperatures and Curie point of the crystal both in [001] and [111] directions were determined by the vibrating sample magnetometer (VSM) and magnetization balance (MB). The magnetic-field-induced strains were measured by strain gauges through the KJC magnetic measuring system. In [001] direction, the as-grown single crystal exhibits a high saturation magnetization of 124 Am².kg^-1, which is nearly doubled compared with that of Ni₂MnGa. A reversible strain of 3% was induced by an applied pulse niagnetic field of 2 T along [001] direction at a temperature (180K) in the range between Ms and Md, that is ten times more than that of Ni₂MnGa. While applying the pulsed magnetic field at temperatures below Ms (such as 155K and 145K), a recoverable field induced strain of 1% was obtained and about 0.5% strain was retained. After heating to room temperature, about 60% whole strain was recovered. If applying magnetic field along [111] direction of the crystal, no visible strain could be induced. According to the martensitic transformation theory on FCC to HCP structure, a mechanism based on the movement of a/6<112> partial dislocations driven by an applied magnetic field is presented.