Electronic structure of Co-Pt alloys: X-ray spectroscopy and density-functional calculations

The K and $L_{2,3}$ absorption edges and core-level binding-energy shifts for pure Co and Pt, and Co-Pt alloys are measured to investigate the changes in electronic structures of Co-Pt alloys. The results agree well with those of the first-principles calculations of the electronic structures by using a full-potential linearized-augmented-plane-wave method. It is found that there is an enhancement of the hybridization between the Co $3d$ and Pt $5d$ orbitals upon alloying. Consequently, as the Pt concentration increases, both Pt and Co gains d electrons, and there is a concomitant decrease in s and p electrons at both sites. This enhanced hybridization in the alloy leads to a net charge transfer from the Co to Pt site in accordance with the predictions based on the electronegativity. For the core-level shifts in Co-Pt alloys the initial-state effects are more important to the Pt $4f$ level, while the relaxation effects play a more important role for the Co $2p$ level.