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

TL;DR

This study uses $^{75}$As NMR and NQR to reveal ferromagnetic spin fluctuations and a peculiar band structure in the metallic compound SrFe4As12, contributing to understanding its magnetic properties.

Contribution

First detailed NMR/NQR investigation of SrFe4As12 revealing ferromagnetic correlations and band structure effects in this filled skutterudite.

Findings

Ferromagnetic spin fluctuations are present in SrFe4As12.

The compound exhibits a broad maximum in susceptibility and relaxation rate around 50-70 K.

A concave-shaped band structure near the Fermi energy explains the temperature dependence.

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/$T_1T$, 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 $1/T_1T$ 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 $1/T_1T$ and $K$ at low temperatures.