Suppression of ferromagnetic spin fluctuations in the filled skutterudite superconductor SrOs4As12 revealed by 75As NMR-NQR measurements

Abstract

Motivated by the recent observation of ferromagnetic spin correlations in the filled skutterudite SrFe${}_4$As${}_{12}$ [Ding et al., Phys. Rev. B 98, 155149 (2018)], we have carried out ${}^{75}$As nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements to investigate the role of magnetic fluctuations in a newly discovered isostructural superconductor SrOs${}_4$As${}_{12}$ with a superconducting transition temperature of $T_{\mathrm{c}}$ $\sim$ 4.8 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 SrFe${}_4$As${}_{12}$, we found that the values of $|K|$ and $1/T_{1}T$ in SrOs${}_4$As${}_{12}$ are smaller than those in SrFe${}_4$As${}_{12}$, indicating no obvious ferromagnetic spin correlations in SrOs${}_4$As${}_{12}$. From the temperature dependence of 1/$T_1$ in the superconducting state, an $s$-wave superconductivity is realized.

8 pages, 5 figures, accepted for publication in Phys. Rev. B. arXiv admin note: substantial text overlap with arXiv:1810.08302