Evidence for ferromagnetic fluctuations in filled skutterudite LaFe4Sb12 : Sb-NQR and La-NMR

摘要

We report the results of Sb-121.121-nuclear quadrupole resonance (NQR) and La-139-NMR measurements on a filled skutterudite antimonide LaFe4Sb12 in order to investigate the magnetic properties at low temperatures from a microscopic point of view. The nuclear spin-lattice relaxation time T-1 of Sb nuclei deviates from the relation T1T = constant above 4.2 K, where 1/T1T has a Curie-Weiss temperature dependence 1/T1T = C/(T + theta) with theta similar to 30 K. The temperature dependence of the Knight shift of La-139 nuclei, which is related to the susceptibility at q = 0, is scaled to that of I IT, T above 40 K. This relation strongly suggests that ferromagnetic fluctuations are predominant in LaFe4Sb12. We also point out that LaFe4Sb12 is situated close to the ferromagnetic instability due to the small Weiss temperature in the Curie-Weiss behavior of I IT, T and the Knight shift.