Annual Review 2024-2025

M A G N E T I C M AT E R I A L S G R O U P A N N U A L R E V I E W 2 0 2 4 / 2 5 22 XMCD fingerprints expose altermagnetism Traditionally, collinear magnetic materials have been classified as ferromagnets or antiferromagnets. Magnetism arises from electron spin, and in ferromagnets the spins all point in the same direction. In antiferromagnets, they point in opposite directions, cancelling each other out. Altermagnets are a new class of magnetic materials that possess the useful properties of both ferromagnets and antiferromagnets, potentially making them very useful in future electronic devices based on spintronics – technology that uses the spin-state of electrons to carry information. However, identifying altermagnetism is challenging. X-ray Magnetic Circular Dichroism (XMCD) is a standard way for investigating ferromagnetic materials, which shows the difference in absorption between left- and right-circularly polarised light. In a non-magnetic sample, and in antiferromagnets, no difference is observed. However, if the spins in an altermagnet are aligned, a signal is observed. A team of researchers from the UK, Japan, Austria, Germany and the Czech Republic theoretically predicted an altermagnetism fingerprint in manganese telluride (α-MnTe). They used XMCD on Diamond’s I06 beamline to detect it experimentally. If you cool down altermagnetic α -MnTe, the magnetic moments align in one of six different directions, and regions in which the moments align in one particular direction are called domains. Using XMCD, researchers are now able to detect the domains and visualise their location in the sample, things that previously have been extremely difficult. Their results demonstrate that XMCD is an effective method of identifying altermagnetic materials, a discovery that could accelerate the use of these new properties in next-generation electronic devices. DOI: 10.1103/PhysRevLett.132.176701 The Mn site-resolved contributions to XMCD calculated by the LDA+DMFT AIM for the Néel vector L Ⅱ [1⁢1¯⁢00] and the light propagation vector k Ⅱ L (a) and k Ⅱ L (b). (c) A cartoon view along the c-axis of the possible domain structure with the six easy-axis orientations of L . The domains with even labels (red) contribute Δ⁢F⁢(ω) with positive prefactor, the odd ones (blue) with negative prefactor. The red and blue dots indicate the positive and negative orientation of the out-of-plane magnetisation m . (d) The out-of-plane canting of the moments in 6 T applied field does not strongly depend on the domain’s L (The domain sizes and shapes were chosen randomly and are not intended to have physical meaning.) L ll [1100] Photon Energy (eV) (d) B=6T MnL 2,3 intensity (arb. units) (c) B=0