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.