Ferromagnetic spin fluctuations in the filled skutterudite SrFe4As12 revealed by 75As NMR-NQR measurements

Abstract

${}^{75}$As nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements have been carried out to investigate the magnetic and electronic properties of the filled skutterudite metallic compound SrFe${}_4$As${}_{12}$. The temperature dependence of Knight shift $K$ determined by the NQR spectrum under a small magnetic field ($\le$ 0.5 T) shows the similar temperature dependence of the magnetic susceptibility $\chi$ which exhibits a broad maximum at $T^{\ast }$ $\sim$ 50 K. The nuclear spin-lattice relaxation rate divided by temperature, 1/$T_{1}T$, increases with decreasing temperature and exhibits a broad maximum at $T$ $\sim$ 70 K, similar to the case of $\chi$. The temperature dependence of $K$ and $1/T_{1}T$ is reasonably explained by a simple model where we assume a concave-shaped band structure near the Fermi energy. Based on a Korringa ratio analysis using the $T_1$ and $K$ data, ferromagnetic spin fluctuations are found to exist in SrFe${}_4$As${}_{12}$. These results indicate that SrFe${}_4$As${}_{12}$ can be characterized to be a metal with ferromagnetic correlations and also the peculiar band structure responsible for the suppression of $1/T_{1}T$ and $K$ at low temperatures.

7 pages, 5 figures, accepted for publication in Phys. Rev. B