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 Angstrom and c = 3.630 +/- 0.001 Angstrom for the FCT martensite, and a0 = 3.756 +/- 0.001 Angstrom 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 degreesC. The saturation magnetization from VSM data is ms = 1220 +/- 10 emu/cm3 at -20 degreesC for the martensite and ms = 1080 +/- 10 emu/cm3 at 60 degreesC 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 x 10(3) erg/cm(3) for the austenite at 60 degreesC, and the tetragonal anisotropy constant K-1 + K-2 is 3.41 +/- 0.02 x 10(5) erg/cm(3) for the martensite at a temperature of -20 degreesC and under 8 MPa of compressive stress in the [0 0 1] direction. (C) 2003 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.