Magnetic anisotropy and intermediate valence in CeCo$_5$ ferromagnet

Abstract

The intermediate valence of Ce in CeCo$_5$ challenges standard density functional theory (DFT) and static DFT+$U$ approaches, which fail to capture its magnetic properties. By combining DFT+$U$ with exact diagonalization of the Anderson impurity model for the Ce 4$f$ shell, we find a substantial reduction of Ce spin and orbital moments, consistent with DFT+DMFT, arising from Ce$^{4+}$ - Ce$^{3+}$ valence fluctuations. The total magnetic moment of 6.70 $μ_B$ agrees with experiment, and the calculated $4f$ density of states reproduces photoemission and Bremsstrahlung isochromat spectra. The uniaxial magnetic anisotropy energy reaches 4.8 meV/f.u. when Coulomb correlations on both Ce 4$f$ and Co 3$d$ shells are included, in very good agreement with experimental data. These results highlight the importance of dynamical correlations and provide guidance for exploring high-performance, low-rare-earth-content permanent magnets.

Figures (1)

• Figure 1: Density of states (DOS) for CeCo$_5$: (A) Spin-resolved Ce-$f$ and Co-$d$ projected DOS from DFT(LSDA); (B) Spin-resolved Ce-$f$ projected DOS from DFT+U(HIA) and DFT+U(ED); (C) Total Ce-$f$ projected DOS from DFT+U(HIA) and DFT+U(ED) compared with experimental PES imada2001 and BIS hillebrecht1984 spectra. The experimental PES and BIS spectra are shown in arbitrary units. All theoretical spectra are aligned so that the Fermi level is at $E=0$.