Coexistence of antiferromagnetic and ferromagnetic spin correlations in   Ca(Fe1-xCox)2As2 revealed by 75As nuclear magnetic resonance
  Recent nuclear magnetic resonance (NMR) measurements revealed the coexistence of stripe-type antiferromagnetic (AFM) and ferromagnetic (FM) spin correlations in both the hole- and electron-doped BaFe$_2$As$_2$ families of iron-pnictide superconductors by a Korringa ratio analysis. Motivated by the NMR work, we investigate the possible existence of FM fluctuations in another iron pnictide superconducting family, Ca(Fe$_{1-x}$Co$_x$)$_2$As$_2$. We re-analyzed our previously reported data in terms of the Korringa ratio and found clear evidence for the coexistence of stripe-type AFM and FM spin correlations in the electron-doped CaFe$_2$As$_2$ system. These NMR data indicate that FM fluctuations exist in general in iron-pnictide superconducting families and thus must be included to capture the phenomenology of the iron pnictides. 
J. Cui, P. Wiecki, S. Ran, S. L. Bud'ko, P. C. Canfield, and Y.   Furukawa
cond-mat.supr-con cond-mat.str-el