Effects of doping on the magnetic anisotropy energy inSmCo5−xFexandYCo5−xFex

Abstract

${\mathrm{SmCo}}_{5}$ is a technologically important material, having one of the largest magnetic anisotropy energies (MAE) of any hard magnet system. Common dopants include Fe and Cu, which produce grain boundaries that align individual grains, but also unintentionally dope the material within the grains. We have studied the magnetic properties of ${\mathrm{SmCo}}_{5\ensuremath{-}x}{\mathrm{Fe}}_{x}$ and ${\mathrm{YCo}}_{5\ensuremath{-}x}{\mathrm{Fe}}_{x}$ using density-functional theory calculations where the Sm $4f$ bands are treated within the $\mathrm{L}\mathrm{D}\mathrm{A}+U$ formalism (LDA---local-density approximation). Both supercell and virtual-crystal approximation calculations were performed for a series of Fe dopings. A strongly nonmonotonic behavior was found in the MAE for both series of compounds. The MAE of ${\mathrm{SmCo}}_{5\ensuremath{-}x}{\mathrm{Fe}}_{x}$ with $\ensuremath{\sim}3--4%$ doping and of ${\mathrm{YCo}}_{5\ensuremath{-}x}{\mathrm{Fe}}_{x}$ with $\ensuremath{\sim}6--7%$ doping increase by about 1 meV/f.u. before falling rapidly with larger Fe dopings. In both these cases, the results can be related to the position of the Fermi level with respect to the Co $3d$ minority peak in the density of states.