Study of Fe₃Pd and related alloys for ferromagnetic shape memory

Ferromagnetic shape memory refers to the behavior of certain alloys that undergo a reversible martensitic transformation and are also ferromagnetic. They undergo the usual shape memory effect by changing temperature, and they can also be made to undergo large changes of shape by applying a magnetic field. Alloys with composition near Fe₃Pd undergo a highly reversible FCC to FCT transformation, have high saturation magnetization approximately 2/3 to that of Fe at room temperature, and therefore are good candidates for ferromagnetic shape memory. In this paper, the possibility of inducing a change of shape by rearranging variants of martensite with an applied field is explored. A key measurement for assessing this possibility is the magnetic anisotropy of a single variant of martensite. We measure this property by applying the appropriate stress to a single crystal to completely detwin it. Magnetization curves for the detwinned crystal are measured and the measurements are corrected for shape anisotropy and the stress. These measurements also settle an apparent discrepancy between the easy axis expected on the basis of Density Functional Theory (DFT) calculation with spin (c-axis), and those inferred from magnetomechancial measurements of James and Wuttig (a-axis).