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

Abstract

Magnetic topological insulators exhibit unique electronic states due to the interplay between the electronic topology and the spin structure. The antiferromagnetic metal $\mathrm{EuI}{\mathrm{n}}_2\mathrm{A}{\mathrm{s}}_2$ 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 ${\mathrm{Eu}}^{2+}$ moments. Here, we report experimental results of the nuclear magnetic resonance (NMR) measurements of all the nuclei in $\mathrm{EuI}{\mathrm{n}}_2\mathrm{A}{\mathrm{s}}_2$ to investigate the coupling between the magnetic moments in the Eu ions and the conduction electrons in $\mathrm{I}{\mathrm{n}}_2\mathrm{A}{\mathrm{s}}_2$ layers and the magnetic structure. The ${}^{75}\mathrm{As}$ and ${}^{115}\mathrm{In}$ NMR spectra observed at zero external magnetic field reveal the appearance of internal fields of $4.9$ and $3.6\mathrm{T}$ respectively at the lowest temperature, suggesting a strong coupling between the conduction electrons in the $\mathrm{I}{\mathrm{n}}_2\mathrm{A}{\mathrm{s}}_2$ layer and the ordered magnetic moments in the Eu ions. The ${}^{75}\mathrm{As}$ 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 $0.7\mathrm{T}$. 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.

19 pages, 6 figures

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Cited by in corpus (2)

• Nature of field-induced transitions and hysteretic magnetoresistance in non-collinear antiferromagnet EuIn2As2
• Non-relativistic linear Edelstein effect in helical EuIn2As2