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

Martensitic phase transformations in an Fe7Pd3 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 a0=3.756±0.001 A for the FCC austenite. The latent heat of the FCC-FCT transformation is 10.79±0.01 J/cm3. A Susceptibility Kappa bridge measurement determined the Curie temperature to be 450 deg. C. The saturation magnetization from VSM data is ms=1220±10 emu/cm3 at -20 deg. C for the martensite and ms=1080±10 emu/cm3 at 60 deg. 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 K1 is -5±2x103 erg/cm3 for the austenite at 60 deg. C, and the tetragonal anisotropy constant K1+K2 is 3.41 ± 0.02 x 105 erg/cm3 for the martensite at a temperature of -20 deg. C and under 8 MPa of compressive stress in the [0 0 1] direction