Sb NQR Study of Ferromagnetic Instability in Alkaline-Earth-Filled Skutterudites SrFe₄Sb₁₂ and BaFe₄Sb₁₂

Abstract

We report a ^121,123Sb nuclear quadrupole resonance (NQR) study of SrFe₄Sb₁₂ and BaFe₄Sb₁₂. The absence of hyperfine splitting or marked broadening in NQR spectra even at the lowest temperature (1.5 K) suggests the absence of uniform ferromagnetic ordering in both compounds. The nuclear spin-lattice relaxation rate divided by temperature, 1⁄T₁T, does not follow the Korringa law, but shows a broad maximum at around 60 K. At temperatures higher than 80 K, 1⁄T₁T can be decomposed into two terms, (1⁄T₁T)₀=const. and T-dependent (1⁄T₁T)_spin. The component (1⁄T₁T)_spin is proportional to χ_spin, which suggests that the present system is close to ferromagnetic instability, whereas below 60 K, (1⁄T₁T)_spin decreases to zero, being unexpected in typical nearly or weakly ferromagnetism.