Coexistence of antiferromagnetic and ferromagnetic spin correlations in Ca(Fe$_{1-x}$Co$_{x})_{2}$As$_{2}$ studied by$^{\, 75}$As NMR
ORAL
Abstract
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.[1] Motivated by the NMR work, we have carried out $^{75}$As NMR measurements in another iron pnictide superconducting family, Ca(Fe$_{1-x}$Co$_{x})_{2}$As$_{2\, }$[2] in order to investigate magnetic fluctuations, especially focusing on possible existence of FM fluctuations. By analyzing $^{75}$As NMR data, we found clear evidence for the coexistence of stripe-type AFM and FM spin correlations in the Ca(Fe$_{1-x}$Co$_{x})_{2}$As$_{2\, }$system. In this talk, we discuss the characteristic magnetic fluctuations in the system. [1] P. Wiecki, et al., Phys. Rev. Lett. \textbf{115}, 137001 (2015). [2] J. Cui, et al., Phys. Rev. B \textbf{92}, 184504 (2015); J. Cui, et al., Phys. Rev. B (in print).
*Supported by USDOE under Contract No. DE-AC02-07CH11358.
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