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.

Diamond Light Source Harwell Science and Innovation Campus Didcot UK

Institut de Physique École Polytechnique Fédérale de Lausanne Lausanne Switzerland

Institute of Physics Czech Academy of Sciences Prague Czech Republic

Institute of Physics Johannes Gutenberg University Mainz Germany

MAX 4 Laboratory Lund Sweden

Max Planck Institute for Chemical Physics of Solids Dresden Germany

Max Planck Institute for the Physics of Complex Systems Dresden Germany

Nanoscale and Microscale Research Centre University of Nottingham Nottingham UK

Photon Science Division Paul Scherrer Institut Villigen Switzerland

School of Physics and Astronomy University of Nottingham Nottingham UK

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