Magnetoelastic and thermoelastic shape memory effect in a Co-Ni single crystal

This letter reports on a study of the magnetomechanical and thermomechanical behavior of a Co-32Ni single crystal. When magnetized along the [001](fcc) direction at room temperature in austenite coexited with martensitic state, field-induced strains as high as 4.2% were measured at a field of 12 kOe. The magnetic field-induced strains were recovered during demagnetization, exhibiting a magnetic hysteresis of 5-6 kOe. No field-induced strain was detected if a magnetic field was loaded along another direction. When deformed in compression along the [001](fcc) direction at room temperature to a prestrain of 5.4%, about 1.5% strain was recovered during subsequent heating, yielding a recovery rate of 27.8%. For specimens deformed in other crystal directions, no obvious recoverable strain was measured. These experimental phenomena are discussed and interpreted in terms of reversible motions of Shockley partial dislocations. (C) 2003 American Institute of Physics.