Cu substitution effects on the local magnetic properties of Ba(Fe_[1-x]Cu_[x])2As2: a site-selective 75-As and 63-Cu NMR study

TL;DR

This study uses site-selective NMR to investigate how Cu substitution affects local magnetic properties in Ba(Fe$_{1-x}$Cu$_x$)$_2$As$_2$, revealing weaker suppression of spin fluctuations than expected and emphasizing local effects.

Contribution

It provides new insights into the local magnetic effects of Cu substitution in Ba(Fe$_{1-x}$Cu$_x$)$_2$As$_2$ using site-selective NMR, challenging simple band models.

Findings

Cu substitution weakens antiferromagnetic spin fluctuations more than expected.

Spin fluctuations are suppressed locally at Cu and neighboring Fe sites.

Absence of a large superconducting dome is linked to magnetic ordering under orthorhombic distortion.

Abstract

We take advantage of the site-selective nature of the $^{75}$As and $^{63}$Cu NMR techniques to probe the Cu substitution effects on the local magnetic properties of the FeAs planes in Ba(Fe$_{1-x}$Cu$_x$)$_2$As$_2$. We show that the suppression of antiferromagnetic Fe spin fluctuations induced by Cu substitution is weaker than a naive expectation based on a simple rigid band picture, in which each Cu atom would donate 3 electrons to the FeAs planes. Comparison between $^{63}$Cu and $^{75}$As NMR data indicates that spin fluctuations are suppressed at the Cu and their neighboring Fe sites in the tetragonal phase, suggesting the strongly local nature of the Cu substitution effects. We attribute the absence of a large superconducting dome in the phase diagram of Ba(Fe$_{1-x}$Cu$_x$)$_2$As$_2$ to the emergence of a nearly magnetically ordered FeAs planes under the presence of orthorhombic distortion.