Coexistence of antiferromagnetic and ferromagnetic spin correlations in Ca(Fe1-xCox)2As2 revealed by 75As nuclear magnetic resonance

摘要

Recent nuclear magnetic resonance (NMR) measurements revealed the coexistenceof stripe-type antiferromagnetic (AFM) and ferromagnetic (FM) spin correlationsin both the hole- and electron-doped BaFe$_2$As$_2$ families of iron-pnictidesuperconductors by a Korringa ratio analysis. Motivated by the NMR work, weinvestigate the possible existence of FM fluctuations in another iron pnictidesuperconducting family, Ca(Fe$_{1-x}$Co$_x$)$_2$As$_2$. We re-analyzed ourpreviously reported data in terms of the Korringa ratio and found clearevidence for the coexistence of stripe-type AFM and FM spin correlations in theelectron-doped CaFe$_2$As$_2$ system. These NMR data indicate that FMfluctuations exist in general in iron-pnictide superconducting families andthus must be included to capture the phenomenology of the iron pnictides.