Phase transformation and magnetic anisotropy of an iron-palladium ferromagnetic shape-memory alloy

Abstract Martensitic phase transformations in an Fe 7 Pd 3 alloy were studied using various experimental techniques: visual observation, differential scanning calorimeter (DSC) measurements and X-ray diffraction. Magnetic measurements on this alloy were made using a vibrating sample magnetometer (VSM) and a Susceptibility Kappa bridge. The VSM measurements were made with the sample in a compression fixture to bias the martensite phase to a single variant. Both X-ray and DSC measurements show that the FCC–FCT transformation is a weak first-order thermoelastic transition. The average lattice parameters are a =3.822±0.001 A and c =3.630±0.001 A for the FCT martensite, and a 0 =3.756±0.001 A for the FCC austenite. The latent heat of the FCC–FCT transformation is 10.79±0.01 J/cm 3 . A Susceptibility Kappa bridge measurement determined the Curie temperature to be 450 °C. The saturation magnetization from VSM data is m s =1220±10 emu/cm 3 at −20 °C for the martensite and m s =1080±10 emu/cm 3 at 60 °C for the austenite. The easy axes of a single variant of FCT martensite are the [1 0 0] and [0 1 0] directions (the a -axes of the FCT lattice) and the [0 0 1] direction (FCT c -axis) is the hard direction. The cubic magnetic anisotropy constant K 1 is −5±2×10 3 erg/cm 3 for the austenite at 60 °C, and the tetragonal anisotropy constant K 1 + K 2 is 3.41 ± 0.02 × 10 5 erg/cm 3 for the martensite at a temperature of −20 °C and under 8 MPa of compressive stress in the [0 0 1] direction.

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