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arXiv · 2409.13211

Incommensurate magnetic order in an axion insulator candidate EuIn$_2$As$_2$ investigated by NMR measurement

Hikaru Takeda·Jian Yan·Zhongzhu Jiang·Xuan Luo·Yuping Sun·Minoru Yamashita
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Abstract

Magnetic topological insulators exhibit unique electronic states due to the interplay between the electronic topology and the spin structure. The antiferromagnetic metal $\rm{EuIn_2As_2}$ is a prominent candidate material in which exotic topological phases, including an axion insulating state, are theoretically predicted depending on the magnetic structure of the $\rm{Eu}^{2+}$ moments. Here, we report experimental results of the nuclear magnetic resonance (NMR) measurements of all the nuclei in $\rm{EuIn_2As_2}$ to investigate the coupling between the magnetic moments in the Eu ions and the conduction electrons in $\rm{In_2As_2}$ layers and the magnetic structure. The $^{75}\rm{As}$ and $^{115}\rm{In}$ NMR spectra observed at zero external magnetic field reveal the appearance of internal fields of $4.9$ and $3.6\ \rm{T}$ respectively at the lowest temperature, suggesting a strong coupling between the conduction electrons in the $\rm{In_2As_2}$ layer and the ordered magnetic moments in the Eu ions. The $^{75}\rm{As}$ NMR spectra under in-plane external magnetic fields show broad distributions of the internal fields produced by an incommensurate fan-like spin structure which turns into a forced ferromagnetic state above $0.7\ \rm{T}$. We propose a spin reorientation process that an incommensurate helical state at zero external magnetic field quickly changes into a fan state by applying a slight magnetic field.

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Hikaru Takeda, Jian Yan, Zhongzhu Jiang, Xuan Luo, Yuping Sun, Minoru Yamashita. 2024-09-20. Incommensurate magnetic order in an axion insulator candidate EuIn$_2$As$_2$ investigated by NMR measurement. https://doi.org/10.1038/s41535-024-00680-0

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