Interactions and phase transformations in Fe-Pd

Interactions in Fe-Pd were studied using diffuse x-ray scattering and first-principles calculations. Diffuse x-ray scattering was performed from single crystals of Fe-38.2 at. % Pd and Fe-81.0 at. % Pd to investigate states of thermal equilibrium at 1023 K and 1073 K, respectively. Short-range-order scattering was separated and effective pair interaction (EPI) parameters were determined using the inverse Monte Carlo method. The EPI parameters are found to strongly vary with respect to data from a previous investigation of Fe-50 at. % Pd. Electronic-structure calculations of effective cluster interaction (ECI) parameters for these states showed the importance of considering multibody interactions and applying the disordered local moment model of the magnetic state: in the ferromagnetic model, the strength of the interactions gets overestimated. Close agreement is reached for short-range order between calculations and the present scattering experiments. Using either a linear compositional variation of the EPI parameters or ECI parameters for alloys with other Pd fractions, the shape of the order-disorder transition line on the Pd-rich side could be reproduced.