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

TL;DR

This study uses NMR to reveal that both antiferromagnetic and ferromagnetic spin correlations coexist in Ca(Fe$_{1-x}$Co$_x$)$_2$As$_2$, suggesting FM fluctuations are common in iron-pnictide superconductors.

Contribution

It demonstrates the presence of ferromagnetic fluctuations in Ca(Fe$_{1-x}$Co$_x$)$_2$As$_2$, extending the understanding of magnetic correlations in iron-pnictide superconductors.

Findings

Coexistence of AFM and FM correlations confirmed in Ca(Fe$_{1-x}$Co$_x$)$_2$As$_2$

FM fluctuations are likely a general feature in iron-pnictide superconductors

NMR Korringa ratio analysis is effective for detecting magnetic correlations

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. 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.