Magnetic Configurations of an Altermagnet: An Atomic-Scale View ✛ ✦
Context
Conventional magnets are divided into ferro- and antiferromagnets, but the recently discovered class of altermagnets challenges this dichotomy. In them, thanks to crystal lattice symmetry (a law established by Emmy Noether), spin splitting of electronic bands arises even with zero net magnetization. Such materials promise a revolution in spintronics, yet experimentally confirming altermagnetic order has proven tricky: photoemission spectroscopy methods only see momentum splitting, which different magnetic structures can produce. To reveal the true nature of the magnetic order, one must peek into real space—and here scanning tunneling microscopy comes to the rescue.
Methods
In work carried out at the Institute of Physics of the Chinese Academy of Sciences, they used spin-polarized STM (a Nobel Prize-winning development, where John Bardeen laid the foundations of tunneling, and Leo Esaki discovered the tunnel effect) cooled to ultra-low temperatures, where decoherence is suppressed. The key tool was visualization of quasiparticle interference (QPI)—a method akin to how ripples on water betray underwater rocks. Electron scattering off defects creates standing waves, from which the band structure can be reconstructed. By switching the probe's magnetization with an external field and observing changes in QPI patterns, they managed to read out the spin polarization of individual surface patches.
Results
Analysis showed that in the V2O layers, vanadium atom spins form a checkerboard pattern, where neighboring atoms have opposite orientations in accordance with the Pauli exclusion principle. This matches predictions for a d-wave altermagnet. But the main surprise awaited at the cleavage steps: different terraces of the same sample exhibited sometimes similar, sometimes opposite spin textures. This means that in KV2Se2O, C-type (altermagnetic) and G-type (conventional antiferromagnetic) configurations coexist, separated by an energy of only about 1 meV—negligible compared to the thermal energy at room temperature. This dualism explains the contradictions in previous experiments: first-principles calculations predicted the G-type as slightly more favorable, but the weak interlayer coupling allows the C-type as well.
Implications
The discovery of coexisting magnetic phases in a single crystal forces a revision of the criteria for identifying altermagnets. It shows that momentum-space methods like ARPES, insensitive to interlayer spin structure, can be misleading. Now, to confidently claim altermagnetism, one must combine momentum-space spectroscopy with direct real-space probing. This is especially crucial for the search for materials with tailored spin properties for spintronic devices.
Future development
Further research could aim at controlling the magnetic state via external stimuli—strain, electric fields, or nanostructuring. If the altermagnetic phase can be stabilized at room temperature, it would pave the way to practical spin-current devices. Moreover, the technique tested on KV2Se2O can be extended to other families of layered oxychalcogenides and possibly to van der Waals heterostructures.
Impact
The results will impact fundamental magnetism physics and materials science, as well as the development of spintronic devices, where precise knowledge of magnetic symmetry is critical.
Next steps
Immediate next steps include studying the temperature evolution of magnetic configurations, finding ways to switch between C- and G-phases, and adapting QPI methods with spin resolution for other altermagnets.
Key open problems
This work is directly linked to the problem of identifying and classifying new types of magnetic order, and to the broader question of how weak perturbations (strain, surface effects) affect competing quantum phases, which requires accounting for decoherence effects in low-dimensional systems.
The knowledge machine's view
This section is addressed to the author of the paper and their colleagues. Neighbouring works were found by meaning-based search across our archive, not by word overlap. We do not review: we show the field around the work.
What the work does
The study employed spin-polarized STM at ultra-low temperatures to visualize quasiparticle interference in KV2Se2O. It was shown that on different terraces, an altermagnetic C-type and an antiferromagnetic G-type configuration coexist, separated by an energy of ~1 meV.
Where its strength is
Direct real-space observation of two magnetic phases coexisting in a single crystal, and demonstration that momentum-resolved methods can yield an ambiguous picture for altermagnets.
Where it could go next
- It might be interesting to compare the observed dualism with the symmetry-based classification of magnetic states proposed in a related work: it provides a formal criterion to distinguish an altermagnet from an antiferromagnet by point group, which would help systematize the conditions for the appearance of C- and G-phases.based on: How to Spot Hidden Magnetism by Symmetry arXiv:2605.27151
- Since two competing magnetic configurations with a small energy gap were found in this work, a nearby study explored similar dualism in another material: perhaps one can draw ideas from it on how to control the relative stability of phases by external stimuli.based on: Magnetic Dualism in a Crystal arXiv:2605.24320
- The spin-polarized STM with atomic resolution used here could naturally be extended to study chiral magnetic textures: the archive contains a work where chiral magnons were visualized in a similar layered system, and an analogous approach would allow investigating spin excitations in KV2Se2O.based on: Plaid Pattern of Chiral Magnons arXiv:2607.02114
Worth trying
- Test whether the magnetic configuration can be switched between C-type and G-type by a local electric field or mechanical strain, using the STM as a tool for manipulation.
- Measure the magnon dispersion on each terrace using inelastic tunneling spectroscopy and compare with calculations for the two phases.
- Investigate the temperature dependence of the relative occupancy of terraces with different configurations to estimate the energy barrier between the phases.
Why this may matter
Understanding the conditions for coexistence and switching between altermagnetic and antiferromagnetic phases could pave the way for devices where the magnetic state is controlled locally, which is important for spintronics and ultrafast memory.
Nearby works in our archive
- How to Spot Hidden Magnetism by Symmetrysimilarity 0.69
- Plaid Pattern of Chiral Magnonssimilarity 0.69
- How to Paint a Magnet with Lightsimilarity 0.68
- Magnetic Tracks with a Secretsimilarity 0.66
- Magnetic Ripples: How Relativity Plays with Spinssimilarity 0.66
- Magnetic Dualism in a Crystalsimilarity 0.66
The closest work in the archive sits at 0.69 by meaning — the usual level for our corpus.
Original abstract
as written by the authors arXiv:2606.29140
Altermagnetism is an emerging class of magnetic order characterized by momentum-dependent spin-split electronic structures despite vanishing net magnetization. Although momentum-space signatures consistent with altermagnetism have been reported in a growing number of materials, their relationship to the underlying real-space magnetic configurations remains incompletely understood, because similar spin-split electronic structures can arise from distinct magnetic orders. In the candidate d-wave altermagnet KV2Se2O, the magnetic origin of the observed momentum-dependent spin splitting has remained controversial. Here, we employ spin-polarized scanning tunnelling microscopy combined with magnetic-field-dependent quasiparticle interference imaging to determine the magnetic configuration of KV2Se2O at the atomic scale. Spin-resolved quasiparticle interference reveals a checkerboard-like antiparallel spin texture within the V2O layer and determines its interlayer spin arrangement across unit-cell step edges. Remarkably, we identify both C-type and G-type magnetic configurations, both of which generate similar spin-split electronic structures at the single-layer level but correspond to d-wave altermagnetic and conventional antiferromagnetic orders, respectively. These observations reveal a complex magnetic landscape arising from nearly degenerate magnetic states. Our results establish a direct connection between momentum-space spin splitting and real-space magnetic order, providing a framework for identifying the microscopic origin of spin-split electronic structures in altermagnetic materials.
Interestingly, cleavage steps, which usually hinder obtaining a perfect surface, played a key role here by allowing a peek into the neighboring layer, as if, by peering around a corner, you saw a mirror reflection of a chessboard.
Key numbers
- QPI modulation period: 0.87 nm
- scattering vector q1, q2: 7.76 nm⁻¹
- hybridization gap: 20 meV
- interlayer exchange interaction: 1 meV
- lattice constant along c: 0.73 nm