Mixed valence nature of the Ce4fstate inCeCo5based on spin-polarizedDFT+DMFTcalculations

Abstract

Cerium-based intermetallics are currently attracting much attention as highly promising alternatives to conventional permanent magnets that contain a scarce rare earth element like neodymium. In the present work we apply a charge fully self-consistent approach combining density functional theory and dynamical mean-field theory (DFT $+$ DMFT) to investigate the magnetization and electronic structure of the ${\mathrm{CeCo}}_{5}$ system. We treat simultaneously the correlation effects in Ce-$4f$ and Co-$3d$ orbitals while taking the spin polarization into account. The calculated magnetic moment corresponding to the Ce-$4f$ shell using the DFT $+$ DMFT method is found to be drastically reduced as compared to the DFT results. Moreover, the Ce-$4f$ valence state fluctuations are evaluated and compared within ${\mathrm{CeCo}}_{5}$ and $\mathrm{Ce}{({\mathrm{Co}}_{0.8}{\mathrm{Cu}}_{0.2})}_{5}$ on account of the trivalent Ce in ${\mathrm{CeCu}}_{5}$. Regarding the Cu substitutions at two Wyckoff positions of Co (2c and 3g), the substitution at 3g sites slightly enhances the magnetic moment of Ce while the substitution at 2c sites leads to nearly vanishing Ce and Co moments. Such a contrast may contribute to the experimentally reported nonmonotonic change of the magnetic anisotropy with increasing Cu alloying content in $\mathrm{Ce}{({\mathrm{Co}}_{1\ensuremath{-}x}{\mathrm{Cu}}_{x})}_{5}$ alloys.