Coexistence of antiferromagnetic and ferromagnetic spin correlations in SrCo2As2 revealed by Co-59 and As-75 NMR

In nonsuperconducting, metallic paramagnetic SrCo2As2, inelastic neutron scattering measurements have revealed strong stripe-type q = (pi, 0) antiferromagnetic (AFM) spin correlations. Here, using nuclear magnetic resonance (NMR) measurements on Co-59 and As-75 nuclei, we demonstrate that stronger ferromagnetic (FM) spin correlations coexist in SrCo2As2. Our NMR data are consistent with density functional theory (DFT) calculations which show enhancements at both q = (pi, 0) and the in-plane FM q = 0 wave vectors in static magnetic susceptibility chi(q). We suggest that the strong FM fluctuations prevent superconductivity in SrCo2As2, despite the presence of stripe-type AFM fluctuations. Furthermore, since DFT calculations have consistently revealed similar enhancements of the chi(q) at both q = (pi, 0) and q = 0 in the iron-based superconductors and parent compounds, our observation of FM correlations in SrCo2As2 calls for detailed studies of FM correlations in the iron-based superconductors.

Complex States