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

TL;DR

This study reveals that cerium's magnetic anisotropy in Ce-Fe intermetallics is intrinsically weak due to Kondo screening, limiting its potential for high-performance permanent magnets.

Contribution

It provides a detailed analysis of the temperature-dependent magnetic anisotropy of cerium in intermetallics, highlighting the effects of nitrogen interstitials and Kondo screening.

Findings

Ce-4f shell is partially Kondo screened in Ce-Fe intermetallics.

Nitrogen interstitials suppress Ce-4f magnetic anisotropy.

Unscreened Ce-4f moments contribute minimally to magnetic hardness at room temperature.

Abstract

Cerium-based intermetallics are currently attracting much interest as a possible alternative to existing high-performance magnets containing scarce heavy rare-earth elements. However, the intrinsic magnetic properties of Ce in these systems are poorly understood due to the difficulty of a quantitative description of the Kondo effect, a many-body phenomenon where conduction electrons screen out the Ce-4f moment. Here, we show that the Ce-4f shell in Ce-Fe intermetallics is partially Kondo screened. The Kondo scale is dramatically enhanced by nitrogen interstitials completely suppressing the Ce-4f contribution to the magnetic anisotropy, in striking contrast to the effect of nitrogenation in isostructural intermetallics containing other rare-earth elements. We determine the full temperature dependence of the Ce-4f single-ion anisotropy and show that even unscreened Ce-4f moments contribute little to the room-temperature intrinsic magnetic hardness. Our study thus establishes fundamental constraints on the potential of cerium-based permanent magnet intermetallics.