Antiferromagnets for functional devices; from electrically switchable metals to “field-free” magnetoelectric surface effects

by Dr Sophie F. Weber (ETH Zürich)

Thursday 4 May 2023, 11:00 → 12:00 Europe/Zurich

WHGA/121

In recent years, antiferromagnets (AFMs) have been rapidly overtaking their ferromagnetic counterparts in spintronics applications. They are insensitive to stray perturbing magnetic fields and have ultrafast magnetization dynamics. AFMs also exhibit a nonvanishing magnetization on certain vacuum-terminated surfaces, and this surface magnetization has far-ranging applications from bulk order parameter readout to exchange bias.

In this talk I will discuss two specific projects on functional AFMs. I will first discuss our collaborative work on the magnetically intercalated transition metal dichalcogenide (TMD) Fe_1/3+xNbS₂. The AFM magnetic order of Fe_1/3+xNbS₂ can be electrically switched at remarkably low current densities, and the spintronics properties are highly sensitive to very small changes in Fe concentration. Our DFT-based analysis, in agreement with optical polarimetry, suggest that the origin of the magnetic switching is a current-induced repopulation of AFM domains.  We also identify in DFT two near-degenerate AFM orders at the 1/3 stoichiometric intercalation. Our analysis combined with neutron data suggest that these two competing orders coexist at perfect stoichiometry, whereas a tiny concentration change leads to the establishment of a single AFM phase. The low-current switching and tunability of magnetic order with minimal doping, as well as the high flexibility in intercalated TMDs in general, make Fe_1/3+xNbS₂ a promising starting point for highly tunable spintronics candidates.

I will then describe our studies of surface magnetization in AFMs. The theoretical prediction and subsequent experimental verification of nonzero magnetization on the (001) surface of magnetoelectric chromia has already attracted much experimental interest as a directly detectable probe of the bulk AFM domain. In some cases, surface magnetisation can even occur on planes which appear to be magnetically compensated. We present DFT calculations demonstrating that a nonzero magnetization does develop on magnetically compensated AFM surfaces when it is allowed by symmetry. Finally, we show that the symmetry and features of the surface magnetization are intimately connected to the symmetries of the bulk magnetoelectric effect.

 

[1] S. F. Weber and J. B. Neaton, Phys. Rev. B 103, 214439 (2021)

[2] S. C. Haley, S. F. Weber et al., Phys. Rev. Research 2, 043020 (2020)

[3] S. Wu, …S. F. Weber et al., Phys. Rev. X 12, 021003 (2022)

[4] S. F. Weber and N. A. Spaldin, Phys. Rev. Lett. 130, 146701 (2023)

[5] A. Urru, S. F. Weber et al., in preparation