  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.
