Intrinsically weak magnetic anisotropy of cerium in potential hard-magnetic intermetallics

We study the magnetic properties of the "1-12" family of prospective hard-magnetic Ce-Fe intermetallics using an ab initio dynamical mean-field theory approach to treat the complex many-electron physics of the Ce 4f¹ shell. By considering the hypothetical binary compound CeFe₁₂, as well as the realistic compositions CeFe₁₁Ti and CeFe₁₁TiN, we show that the localization of the Ce 4f electron is strongly sensitive to alloying and interstitials. The onset of heavy-fermion behavior accompanied by a significant reduction of the Ce-4f moment—and concomitantly its contribution to the magnetic anisotropy—is found to occur in CeFe₁₂ for a wide temperature range up to about 400K. This 4f delocalization is moderately reduced by Ti substitution on the Fe site and, unexpectedly, markedly increased by nitrogen interstitials. However, even for localized Ce-4f electrons their contribution to the magnetic anisotropy is rapidly suppressed with increasing temperature.