Motivated by the recent observation of ferromagnetic spin correlations in the filled skutterudite ${\mathrm{SrFe}}_4{\mathrm{As}}_{12}$ [Q.-P. Ding et al., Phys. Rev. B 98, 155149 (2018)], we have carried out ${}^{75}\mathrm{As}$ nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements to investigate the role of magnetic fluctuations in the newly discovered isostructural superconductor ${\mathrm{SrOs}}_4{\mathrm{As}}_{12}$ with a superconducting transition temperature of $T_{\mathrm{c}}\sim 4.8\mathrm{K}$. Knight shift $K$ determined by the NQR spectrum under a small magnetic field ($\le 0.5$ T) is nearly independent of temperature, consistent with the temperature dependence of the magnetic susceptibility. The nuclear spin-lattice relaxation rate divided by temperature, $1/T_{1}T$, is nearly independent of temperature above $\sim 50$ K and increases slightly with decreasing temperature below the temperature. The temperature dependence is reasonably explained by a simple model where a flat band structure with a small ledge near the Fermi energy is assumed. By comparing the present NMR data with those in ${\mathrm{SrFe}}_4{\mathrm{As}}_{12}$, we found that the values of $\left|K\right|$ and $1/T_{1}T$ in ${\mathrm{SrOs}}_4{\mathrm{As}}_{12}$ are smaller than those in ${\mathrm{SrFe}}_4{\mathrm{As}}_{12}$, indicating no obvious ferromagnetic spin correlations in ${\mathrm{SrOs}}_4{\mathrm{As}}_{12}$. From the temperature dependence of $1/T_1$ in the superconducting state, an $s$-wave superconductivity is realized.

• Received 23 May 2019
• Revised 22 July 2019

DOI:https://doi.org/10.1103/PhysRevB.100.054516