Microscopic study of the effect of impurities on the first order spin density wave transition in BaFe$_2$As$_2$

TL;DR

This study uses $^{75}$As NMR to investigate how impurities like Sn affect the magnetic transition in BaFe$_2$As$_2$, revealing impurity-induced changes in transition order and magnetic order type.

Contribution

It provides new insights into impurity effects on magnetic phase transitions in BaFe$_2$As$_2$ using detailed NMR analysis.

Findings

Sn impurities suppress the magnetic ordering temperature from 138 K to 85 K.

Impurities induce a second order transition to incommensurate magnetic order.

Impurities significantly alter low energy spin fluctuations.

Abstract

We report an $^{75}$As NMR study of BaFe$_2$As$_2$ in both single crystals and polycrystal forms. We find that Sn impurities in the single crystal dramatically alter the low energy spin fluctuations and suppress the ordering temperature from 138 K to 85 K. In contrast to Sn-free samples, we find that the temperature dependence of the $^{75}$As NMR spectra and spin lattice relaxation rates reveal a second order phase transition to a state of incommensurate magnetic order.