Magneto-shape-memory effect in Co-Ni single crystals

A Co-33 wt % Ni single crystal was grown by an optical floating-zone furnace without crucible in a high-purity argon atmosphere. In the [001] direction, the as-grown single crystal exhibited a saturation magnetization of 124 A m(2)/kg, which is nearly twice as high as that of Ni2MnGa, a typical magneto-shape-memory material. A reversible strain of 3% was induced by an applied pulse magnetic field of 2 T in the [001] direction in the temperature range between M-d and M-s. According to the martensitic transformation theory [T. Y. Hsu (Z. Y. Xu), Sci. China, Ser. E: Technol. Sci. 40, 561 (1997)] for fcc (gamma)--> hcp (epsilon), a possible mechanism based on the reversible motion of the Shockley partial dislocations is proposed in this letter. (C) 2001 American Institute of Physics.