(a) shows the crystal and spin structure of MnTe, with manganese atoms in red and blue and tellurium atoms in yellow. (b) illustrates how circularly polarized light produces distinct photoelectron diffraction patterns. Left-circular polarization enhances emission from the spin-up sublattice (A), while right-circular polarization enhances emission from the spin-down sublattice (B) in the opposite direction. The resulting circular dichroism reveals the opposite spin orientations of the sublattices. Credit: Professor Peter Krüger / Chiba University, Japan

Altermagnets are a newly recognized class of antiferromagnets whose magnetic structure behaves very differently from what is found in conventional systems. In conventional antiferromagnets, the sublattices are linked by simple inversion or translation, resulting in spin-degenerate electronic bands. In altermagnets, however, they are connected by unconventional symmetries such as rotations or screw axes. This shift in symmetry breaks the spin degeneracy, allowing for spin-polarized electron currents even in the absence of net magnetization.

This unique property makes altermagnets exciting candidates for spintronic technologies, a field of electronics that utilizes the intrinsic spin of the electrons, rather than just their charge, to store and process information. As spins can flip or switch direction extremely quickly, materials that allow spin-dependent currents could enable faster and more energy-efficient electronic devices.

Challenges in identifying altermagnetic materials

Yet, confirming whether a material is truly altermagnetic is difficult. Even for well-studied candidates like ruthenium dioxide, researchers still disagree about whether it exhibits altermagnetism. This uncertainty highlights the need for experimental methods capable of directly revealing the magnetic arrangement of the sublattices in altermagnetic compounds.

Now, Professor Peter Krüger at the Graduate School of Engineering and Molecular Chirality Research Center, Chiba University, Japan, has developed a way to finally detect this hidden magnetic structure.

New detection method using RPED

By using a technique called resonant photoelectron diffraction (RPED), together with circularly polarized light, he discovered that altermagnets produce a unique "magnetic circular dichroism (CD)" signal in their diffraction patterns—one that changes sign when the handedness of the light wave is reversed.

This response directly exposes the magnetization of each individual sublattice, making the hidden altermagnetic structure visible.

The study was published in the journal Physical Review Letters.

"I devised a new method for measuring the magnetic properties of these new materials, specifically the orientation and size of atomic magnetic moments. With this method, it becomes possible to detect altermagnetism in nano-structured materials, especially thin films, where traditional methods such as neutron scattering fail," says Prof. Krüger.

How the new technique works

The method builds upon X-ray magnetic CD (XMCD), which measures how magnetic atoms absorb left- and right-circularly polarized X-rays differently. However, XMCD generally falls short for altermagnets because the magnetic moments on the A and B sublattices are equal and opposite, causing their signals to cancel.

CD-RPED solves this by merging XMCD with photoelectron diffraction (PED). PED works by ejecting electrons with X-rays; as these electrons escape, they scatter off nearby atoms, creating a unique diffraction pattern for each atomic site.

By tuning the X-ray energy to a resonance of the magnetic atom, the intensity of the diffraction pattern becomes sensitive to the direction of the local magnetic moment. As a result, the patterns produced by left- and right-circularly polarized light differ, giving each sublattice its own magnetic signature.

Validation and future implications

The method was validated using manganese telluride, a well-established altermagnet. The analysis reveals a 180-degree flip in the diffraction pattern under opposite circular polarizations, producing a clear dichroism signal that confirms the proposed technique’s ability to detect altermagnetic order.

"We have shown that the occurrence of magnetic CD in RPED is a direct consequence of the XMCD on each magnetic sublattice and the fact that in an altermagnet, the two sublattices necessarily have distinct PED patterns," says Prof. Krüger.

This breakthrough makes it possible to definitively identify altermagnetism in surfaces, interfaces, and thin films, systems where conventional magnetic probes often fail. Looking ahead, the ability to determine altermagnetic order at the atomic level is expected to accelerate the search for new altermagnetic materials and support the development of future spintronic technologies.

More information: Peter Krüger, Circular Dichroism in Resonant Photoelectron Diffraction as a Direct Probe of Sublattice Magnetization in Altermagnets, Physical Review Letters (2025). DOI: 10.1103/pl1p-v5rs

Citation: Detecting the hidden magnetism of altermagnets (2025, December 26) retrieved 26 December 2025 from https://phys.org/news/2025-12-hidden-magnetism-altermagnets.html

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