Crossover between itinerant ferromagnetism and antiferromagnetic fluctuations in filled skutterudites MFe4Sb12 (M=Na, Ba, La) as determined by NMR

Abstract Nuclear resonance investigations on the 23 Na and the 139 La nuclei in filled skutterudites MFe 4 Sb 12 (M=Na, La) are reported. In contrast to NaFe 4 Sb 12 for the La compound the effective magnetic moment is remarkably lower and the Curie–Weiss temperature is negative which indicates antiferromagnetic correlations. The spin-lattice relaxation rates 1/ T 1 exhibit a qualitatively different temperature behavior which provides clear evidence for dissimilar types of itinerant magnetism in the two compounds. For NaFe 4 Sb 12 1/ T 1 vs. T indicates itinerant ferromagnetism with ordering at T c = 8 5 K , whereas for the La 0.9 Fe 4 Sb 12 weak itinerant antiferromagnetism with no ordering is found. 1/ T 1 is analyzed in terms of Moriya's self-consistent renormalization theory (SCR) for itinerant magnetic materials.