XMCD reveals tunable magnetism in light rare-earth Laves

Researchers probed electronic and magnetic behavior across light rare-earth cubic Laves alloys Nd1-xPrxCoNi and Ce0.25Pr0.75CoNi, plus binary endpoints, using soft x-ray absorption, x-ray magnetic circular dichroism (XMCD), density-functional theory and crystal-field multiplet calculations.

Measurements show transition-metal moments saturate below 1 T, while rare-earth moments remain unsaturated even at 5 T, consistent with van Vleck paramagnetic contributions and crystal-field suppression. The analysis highlights a practical limitation of commonly used XMCD sum rules: accurate element-specific moments for 3d metals require reliable estimates of unoccupied 3d states. Notably, Ni carries a finite magnetic moment, challenging its presumed nonmagnetic role in many Laves compounds.

For light rare-earths the spin sum rule is invalid, so multiplet calculations were used to extract spin moments; remaining moments came from experiment. Nd and Pr retain localized 4f3 and 4f2 configurations but with reduced moments due to crystal-field effects and are robust against rare-earth substitution. Ce shows a tunable mixed-valent ground state (magnetic 4f1 and nonmagnetic 4f0 fractions) that varies with the electronegativity of neighboring 3d metals, offering a compositional route to tune Ce magnetism and inform magnetocaloric material design.