EXAFS investigation of the role of Cu on the chemical order and lattice distortion in L10 FePtCu thin films

In this work we present an Extended X-ray Absorption Fine Structure (EXAFS) characterization of ternary FePtCu alloys with different Cu content. The EXAFS measurements have been carried out at the Cu-K? and Pt-LIII edges in order to describe the local environment around these elements in the FePtCu samples and to compare the structural evolution as a function of the Cu content. The EXAFS study, based on a substitutional model where the Cu atoms occupy Fe or Pt sites in the tetragonal structure, has been performed by using linear dichroism to enhance the sensitivity to differently oriented bonds and to gain a detailed description of the atomic environment. The study allowed to distinguish experimentally the effects on the chemical order and lattice distortion induced by the Cu atoms. We correlate the determined positions of the Cu atoms in the chemically L10 ordered fct lattice with the magnetic properties of FePtCu ternary alloys. In particular, the main effect of Cu atoms in the alloy is a linear reduction of the c/a ratio, while the non-monotonic behaviour of the chemical order is consistent with the variation of the magnetocrystalline anisotropy [1]. [1] S. Laureti et al. Journal of Applied Crystallography 47, (2014) doi:10.1107/S1600576714019268