Altermagnetic nanotextures revealed in bulk <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>Mn</mml:mi><mml:mi>Te</mml:mi></mml:mrow></mml:math>

Altermagnetism represents a magnetic phase in which the combination of compensated antiferromagnetic order with an anisotropic crystal field leads to time-reversal symmetry breaking. The resulting combination of properties typically associated with ferromagnets, but with net-zero magnetization, has generated significant interest for both fundamental research and technological applications. With many candidate altermagnetic materials, <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mrow><a:mi>Mn</a:mi><a:mi>Te</a:mi></a:mrow></a:math> has emerged as one of the most promising systems, with growing experimental evidence for altermagnetic phenomena. So far, the majority of measurements have been performed on thin films, or have involved surface measurements. However, the question of altermagnetic order in the bulk system—in the absence of substrate or surface effects—remains. Here we show evidence for bulk altermagnetism in single-crystal <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mrow><c:mi>Mn</c:mi><c:mi>Te</c:mi></c:mrow></c:math> through spectroscopic x-ray microscopy. By performing nanoscale x-ray magnetic circular dichroic (XMCD) imaging in transmission on a <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:mn>200</e:mn></e:math>-nm-thick lamella, we observe domains and magnetic textures with a spectroscopic signature characteristic of altermagnetic order, thereby confirming the intrinsic nature of altermagnetism in <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"><g:mrow><g:mi>Mn</g:mi><g:mi>Te</g:mi></g:mrow></g:math>. Quantitative analysis of the XMCD signal reveals excellent agreement with predicted signals, establishing that the altermagnetic order exists throughout the thickness of the lamella and confirming the intrinsic, bulk nature of the state. With these results, we demonstrate that transmission XMCD spectroscopic imaging is a robust, quantitative technique to probe altermagnetic order, providing a means to probe individual altermagnetic domains within complex configurations. This ability to investigate and characterize altermagnetic order in bulk crystals represents an important tool for the exploration of altermagnetism across a wide range of candidate materials, of key importance for the development of future technologies.