Form factor analysis in rare-earth intermetallics: Evidence for 5d polarization and higher-order exchange terms

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Abstract
The measurement at low temperature of the form factor of rare earth intermetallics allows the determination of both the 4f localized contribution and an additional magnetization density also centered on the rare‐earth atoms. This contribution, less localized than that of the 4f electrons, is commonly attributed to conduction electrons. We show that the localization of these electrons is nearly the same in many alloys (RAl2, HoFe2...) and similar to that expected for an atomic 5d shell. In addition, the 4f form factor gives a direct determination of the ground state of the rare‐earth ion. This ground state has been proved in several cases (HoAl2, HoFe2, NdCo5...) to be in disagreement with the one deduced from magnetization measurements using crystal‐field an molecular‐field formalism. Such a disagreement must result from higher‐order terms in exchange mechanism.