Evidence for Ferromagnetic Fluctuations in Filled Skutterudite LaFe₄Sb₁₂:Sb-NQR and La-NMR

Abstract

We report the results of ^121,123Sb-nuclear quadrupole resonance (NQR) and ¹³⁹La-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 T₁ 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+θ) with θ∼30 K. The temperature dependence of the Knight shift of ¹³⁹La nuclei, which is related to the susceptibility at q=0, is scaled to that of 1⁄T₁T 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 1⁄T₁T and the Knight shift.