Large magneto-optical Kerr effect and imaging of magnetic octupole domains in an antiferromagnetic metal

Abstract

When a polarized light beam is incident upon the surface of a magnetic material, the reflected light undergoes a polarization rotation1. This magneto-optical Kerr effect (MOKE) has been intensively studied in a variety of ferro- and ferrimagnetic materials because it provides a powerful probe for electronic and magnetic properties2, 3 as well as for various applications including magneto-optical recording4. Recently, there has been a surge of interest in antiferromagnets (AFMs) as prospective spintronic materials for high-density and ultrafast memory devices, owing to their vanishingly small stray field and orders of magnitude faster spin dynamics compared to their ferromagnetic counterparts5–9. In fact, the MOKE has proven useful for the study and application of the antiferromagnetic (AF) state. Although limited to insulators, certain types of AFMs are known to exhibit a large MOKE, as they are weak ferromagnets due to canting of the otherwise collinear spin structure10–14. Here we report the first observation of a large MOKE signal in an AF metal at room temperature. In particular, we find that despite a vanishingly small magnetization of M ~0.002 µB/Mn, the non-collinear AF metal Mn3Sn15 exhibits a large zero-field MOKE with a polar Kerr rotation angle of 20 milli-degrees, comparable to ferromagnetic metals. Our first-principles calculations have clarified that ferroic ordering of magnetic octupoles in the non-collinear Néel state16 may cause a large MOKE even in its fully compensated AF state without spin magnetization. This large MOKE further allows imaging of the magnetic octupole domains and their reversal induced by magnetic field. The observation of a large MOKE in an AF metal should open new avenues for the study of domain dynamics as well as spintronics using AFMs.

Noncollinear antiferromagnetic Mn3Sn films

“…Among many different antiferromagnetic [7][8][9] or artificial antiferromagnetic materials [10,11], the noncollinear chiral antiferromagnets have attracted much interest, due to their remarkable structural, magnetic, and electrotransport properties. The trianglular spin structure of these compounds gives rise to a large anomalous Hall effect (AHE) [12,13], thermoelectric effect [14][15][16], magneto-optical Kerr effect [17,18], and spin Hall effect (SHE) [19]. Inspired by experimental work in Mn 3 Ir [19], ab initio calculations confirmed large anisotropic anomalous Hall current and spin Hall current in these materials [20], while predicting that charge current is also spin polarized [21].…”

Advanced Materials and Device Architectures for Magnetooptical Spatial Light Modulators

“…In most ferri/ferromagnetic films, |θ K | increases proportionally with magnetization, i.e., |θ K | = K s M , with K s being a coefficient within 0.2–2° T −1 (the shaded region in Figure ). Mn 3 Sn, as an antiferromagnetic metal, has a large MOKE with K s = 25.6° T −1 while for antiferromagnetic insulators, K s has a value in the range of 10–20° T −1 …”

“…Mn 3 Sn, an antiferromagnetic metal, has a large MOKE with K s = 25.6° T −1 while for antiferromagnetic insulators, K s has a value in the range of 10–20° T −1 . Reproduced with permission . Copyright 2018, Springer Nature.…”

Electric‐Field Control of Magnetic Order: From FeRh to Topological Antiferromagnetic Spintronics

“…Accordingly, the orientation of the AFM spin axis in FeRh can be controlled by the direction of the cooling field applied above the MPT temperature of FeRh. [96,[98][99][100][101][102][103][104][105] At the same time, another major breakthrough in AFM spintronics came from the discovery of the Berry-curvatureinduced anomalous Hall effect (AHE). Similar to the AMR effect in FM materials, the resistance is higher when the AFM spin axis is parallel to the measuring current and is lower when the AFM spin axis is transverse to the current.…”