¹²¹Sb-NMR Knight shift study of filled skutterudite CeOs₄Sb₁₂

We carried out an ¹²¹Sb nuclear magnetic resonance (NMR) measurement on CeOs₄Sb₁₂ to investigate its electric state. The precise temperature (T) dependence of the Knight shift was obtained by using an aligned powdered sample and NQR parameters. The T dependence of the Knight shift below 300 K can not be explained by the c-f hybridization gap model with 2D = 3000 K and 2Δ = 320 K obtained by the 1/T₁. This result indicates that there is q-dependence in the gap. It was revealed that a ferromagnetic correlation develops with decreasing temperature below 50 K from an increase of the Knight shift. Considering this result and previous 1/T₁ measurements, there are both ferromagnetic and antiferromagnetic fluctuations in CeOs₄Sb₁₂.