Nanoscale imaging and control of altermagnetism in MnTe

Article Nanoscale imaging and control of altermagnetism in MnTe https://doi.org/10.1038/s41586-024-08234-x Received: 3 May 2024 Accepted: 16 October 2024 O. J. Amin1,12 ✉, A. Dal Din1,12 ✉, E. Golias2, Y. Niu2, A. Zakharov2, S. C. Fromage1, C. J. B. Fields1,3, S. L. Heywood1, R. B. Cousins4, F. Maccherozzi3, J. Krempaský5, J. H. Dil5,6, D. Kriegner7, B. Kiraly1, R. P. Campion1, A. W. Rushforth1, K. W. Edmonds1, S. S. Dhesi4, L. Šmejkal7,8,9,10, T. Jungwirth1,11 & P. Wadley1 ✉ Published online: 11 December 2024 Open access Check for updates Nanoscale detection and control of the magnetic order underpins a spectrum of condensed-matter research and device functionalities involving magnetism. The key principle involved is the breaking of time-reversal symmetry, which in ferromagnets is generated by an internal magnetization. However, the presence of a net magnetization limits device scalability and compatibility with phases, such as superconductors and topological insulators. Recently, altermagnetism has been proposed as a solution to these restrictions, as it shares the enabling time-reversal-symmetry-breaking characteristic of ferromagnetism, combined with the antiferromagnetic-like vanishing net magnetization1–4. So far, altermagnetic ordering has been inferred from spatially averaged probes4–19. Here we demonstrate nanoscale imaging of altermagnetic states from 100-nanometre-scale vortices and domain walls to 10-micrometre-scale single-domain states in manganese telluride (MnTe)2,7,9,14–16,18,20,21. We combine the time-reversal-symmetry-breaking sensitivity of X-ray magnetic circular dichroism12 with magnetic linear dichroism and photoemission electron microscopy to achieve maps of the local altermagnetic ordering vector. A variety of spin configurations are imposed using microstructure patterning and thermal cycling in magnetic fields. The demonstrated detection and controlled formation of altermagnetic spin configurations paves the way for future experimental studies across the theoretically predicted research landscape of altermagnetism, including unconventional spin-polarization phenomena, the interplay of altermagnetism with superconducting and topological phases, and highly scalable digital and neuromorphic spintronic devices3,14,22–24. For condensed-matter physics, the d-wave (or higher even-parity wave) spin-polarization order in altermagnets represents the sought-after, but for many decades elusive, counterpart in magnetism of the unconventional d-wave order parameter in high-temperature superconductivity3. For spintronics, altermagnets can merge favourable characteristics of conventional ferromagnets and antiferromagnets, considered for a century as mutually exclusive3. They can combine strong spin-current effects, which underpin reading and writing functionalities in commercial ferromagnetic memory bits, with vanishing net magnetization, enabling demonstrations of high spatial, temporal and energy scalability in experimental antiferromagnetic bits insensitive to external magnetic-field perturbations. These examples, as well as the predicted abundance of altermagnetic materials, ranging from insulators and semiconductors to metals and superconductors, illustrate the expected broad impact of this field on modern science and technology3. So far, however, the unconventional properties of altermagnets have been experimentally detected using spatially averaging electronic transport4–11 or spectroscopy probes12–19. Here we report mapping of the altermagnetic order vector and demonstrate the controlled formation, from nanoscale to microscale, of a rich landscape of altermagnetic textures, including vortices, domain walls and domains. We use polarized X-ray photoemission electron microscopy (PEEM), which is a powerful tool in magnetism, allowing for, in addition to element specificity and magnetic sensitivity, concurrent full-field real-space imaging at the microscale with nanoscale resolution. The measurements were performed at 100 K on a 30-nm-thick film of α-MnTe(0001) deposited on an InP(111)A substrate. Manganese telluride (MnTe) is one of the prototypical materials in altermagnetic research2,7,9,12,14–16,18,20. Below the transition temperature of 310 K, the magnetic order is within the a–b plane of the film. The unit cell, shown School of Physics and Astronomy, University of Nottingham, Nottingham, UK. 2MAX IV Laboratory, Lund, Sweden. 3Diamond Light Source, Harwell Science and Innovation Campus, Didcot, UK. Nanoscale and Microscale Research Centre, University of Nottingham, Nottingham, UK. 5Photon Science Division, Paul Scherrer Institut, Villigen, Switzerland. 6Institut de Physique, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland. 7Institute of Physics, Czech Academy of Sciences, Prague, Czech Republic. 8Max Planck Institute for the Physics of Complex Systems, Dresden, Germany. 9Max Planck Institute for Chemical Physics of Solids, Dresden, Germany. 10Institute of Physics, Johannes Gutenberg University, Mainz, Germany. 11Present address: Institute of Physics, Czech Academy of Sciences, Prague, Czech Republic. 12These authors contributed equally: O. J. Amin, A. Dal Din. ✉e-mail: ; alfred.daldin@ 1 4 nottingham.ac.uk; 348 | Nature | Vol 636 | 12 December 2024 a b +L −L XMLD [C2||C6t1/2] I XMCD I Te Néel vector Mn [1100] d c XMCD XMLD Vector map f e Intensity (a.u.) g Mn L2,3 XAS 1.0 XMCD 0.5 0 ×50 635 640 645 650 655 660 Energy (eV) Fig. 1 | Mapping of the altermagnetic order vector in MnTe. a, Unit cell of α-MnTe with Mn spins collinear to the [11̄00] magnetic easy axis. Applying T transforms the left unit cell into the right. The unit cells with opposite L vector produce the same XMLD but inequivalent XMCD owing to T -symmetry breaking in altermagnetic MnTe. b, Illustration of the vector mapping process. The colour wheels show the angular dependence of the XMCD, three-colour XMLD and six-colour vector map on the in-plane L-vector direction. The XMCD acts on the three-colour XMLD, with light XMCD regions changing the colour and dark XMCD regions leaving it unchanged to produce the six-colour L-vector map. In the XMLD and vector map, coloured segments indicate the magnetic easy axes oriented along the ⟨1100⟩ crystallographic directions. c–e, XMCD-PEEM (c), XMLD-PEEM (d) and vector map (e) of a 25-μm2 region of unpatterned MnTe film. f, An expanded view of the boxed region in e in which a vortex–antivortex pair is identified. The vortex–antivortex core positions are highlighted by the magenta–white and cyan–white circles, respectively. The combination of XMLD-PEEM and XMCD-PEEM imaging allows for unambiguous determination of the helicity of the swirling textures of the altermagnetic order vector, indicated by the six colours and overlaid vector plot. Scale bars, 1 μm (c) and 250 nm (f). g, X-ray absorption spectrum (XAS), plotted in black, and XMCD spectrum, plotted in red, measured across the Mn L 2,3 reson (...truncated)