Structural, magnetic, and defect properties of Co-Pt-type magnetic-storage alloys: Density-functional theory study of thermal processing effects

Abstract

Using an optimized-basis Korringa-Kohn-Rostoker-coherent-potential approximation method, we calculate formation enthalpies $\ensuremath{\Delta}{E}_{f}$, structural, and magnetic properties of paramagnetic (PM) and ferromagnetic, disordered A1 and ordered $\text{L}{1}_{0}$ CoPt, FePd, and FePt systems that are of interest for high-density magnetic-recording media. To address processing effects, we focus on the point defects that dictate thermal properties and planar defects (e.g., $c$ domain and antiphase boundaries) which can serve as pinning centers for magnetic domains and affect storage properties. We determine bulk Curie $({T}_{c})$ and order-disorder $({T}_{\text{o-d}})$ transition temperatures within 4% of observed values, and estimates for nanoparticles. Planar-defect energies ${\ensuremath{\gamma}}_{x}^{hkl}$ show that the favorable $[hkl]$ defects depend on processing conditions as ${T}_{c}l{T}_{\text{o-d}}$ in these alloys, and the PM defects agree with those observed. We correlate all properties with the electronic structure.