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arxiv: 2506.21661 · v1 · submitted 2025-06-26 · ❄️ cond-mat.str-el

Microscopic origin of the magnetic interactions and their experimental signatures in altermagnetic La₂O₃Mn₂Se₂

Laura Garcia-Gassull , Aleksandar Razpopov , Panagiotis Peter Stavropoulos , Igor I Mazin , Roser Valent\'i This is my paper

Pith reviewed 2026-05-19 07:21 UTC · model grok-4.3

classification ❄️ cond-mat.str-el
keywords altermagnetismLa2O3Mn2Se2superexchangeGKA rulesMn2+ ionsinverse Lieb latticemagnetic interactionsmagnon bands
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The pith

In La2O3Mn2Se2, direct exchange plus multiorbital superexchange on Mn2+ ions produces dominant antiferromagnetic nearest-neighbor coupling that stabilizes altermagnetism on the inverse Lieb lattice.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper shows that altermagnetism in La2O3Mn2Se2 demands a large antiferromagnetic nearest-neighbor interaction, even though standard Goodenough-Kanamori-Anderson rules would favor ferromagnetic coupling at the 90-degree bond angle. Ab initio calculations combined with analytical modeling reveal that direct Mn-Mn exchange and multiple superexchange pathways cooperate because each Mn2+ ion has a half-filled d5 shell with five active orbitals. This multiorbital character flips the sign of the 90-degree superexchange to antiferromagnetic and makes it stronger than the 180-degree next-nearest-neighbor term. The resulting exchange hierarchy explains the observed altermagnetic ground state and produces distinctive magnon-band features.

Core claim

The nearest-neighbor exchange in La2O3Mn2Se2 is strongly antiferromagnetic because direct exchange and orbital-dependent superexchange reinforce each other; the five d-orbitals on each Mn2+ ion allow antiferromagnetic contributions at 90 degrees that overcome the usual GKA preference for ferromagnetism, thereby enabling altermagnetic order on the inverse Lieb lattice.

What carries the argument

Multiorbital d5 configuration of Mn2+ ions, which sets the relative strengths and signs of direct exchange versus 90-degree and 180-degree superexchange paths.

If this is right

  • The altermagnetic phase remains the ground state because the nearest-neighbor antiferromagnetic coupling dominates over longer-range terms.
  • Magnon bands display characteristic crossings and splittings that serve as fingerprints of the exchange parameters.
  • The same mechanism accounts for why the material realizes altermagnetism rather than conventional antiferromagnetism or ferromagnetism.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Similar multiorbital d5 chemistry may stabilize altermagnetism on other lattices where 90-degree bonds are present.
  • Small changes in bond angles or lattice parameters could tune the balance between direct and superexchange contributions, offering a route to control the altermagnetic phase.
  • The predicted magnon signatures could be checked with inelastic neutron scattering to confirm the microscopic exchange model.

Load-bearing premise

The chosen ab initio method and Hubbard correction accurately rank the magnitudes of direct exchange against the various orbital-selective superexchange terms.

What would settle it

Neutron-scattering data showing a magnon dispersion with ferromagnetic nearest-neighbor coupling instead of the predicted antiferromagnetic one would disprove the interaction hierarchy.

Figures

Figures reproduced from arXiv: 2506.21661 by Aleksandar Razpopov, Igor I Mazin, Laura Garcia-Gassull, Panagiotis Peter Stavropoulos, Roser Valent\'i.

Figure 1
Figure 1. Figure 1: FIG. 1. (a) Crystal structure of La [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2. (a) Level diagram of the metal and ligands in the [PITH_FULL_IMAGE:figures/full_fig_p003_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3. Estimated dominating isotropic Heisenberg ex [PITH_FULL_IMAGE:figures/full_fig_p005_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: FIG. 4. Spin [PITH_FULL_IMAGE:figures/full_fig_p007_4.png] view at source ↗
Figure 6
Figure 6. Figure 6: FIG. 6. Atomic species resolved density of states for [PITH_FULL_IMAGE:figures/full_fig_p012_6.png] view at source ↗
Figure 7
Figure 7. Figure 7: FIG. 7. Obtained isotropic exchange parameters via TEMA, [PITH_FULL_IMAGE:figures/full_fig_p013_7.png] view at source ↗
read the original abstract

Altermagnets (AM) are a recently introduced type of magnets, with no net magnetization like antiferromagnets, but displaying a non-relativistic Zeeman splitting in reciprocal space like ferromagnets. One of the lately discussed models to realize AM is the inverse Lieb lattice (ILL). Initially suggested as a purely theoretical construct, the ILL occurs in real materials such as La$_2$O$_3$Mn$_2$Se$_2$. However, AM on the ILL requires 90$^\circ$ nearest-neighbor superexchange to be {\it antiferromagnetic} and dominant over the 180$^\circ$ next-nearest-neighbor superexchange, in apparent contradiction to the Goodenough-Kanamori-Anderson (GKA) rules. Yet, AM ordering was found to be the ground state in La$_2$O$_3$Mn$_2$Se$_2$. Combining ab initio and analytical methods, we determine how direct exchange and superexchange act together to produce a large antiferromagnetic nearest-neigbor coupling. The seeming contradiction with the GKA rules is traced back to the multiorbital character of Mn$^{+2}$ ions. By calculating magnon bands, we identify universal signatures of the exchange interactions, suggesting experimental fingerprints.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 2 minor

Summary. The paper investigates the microscopic origin of magnetic interactions in altermagnetic La₂O₃Mn₂Se₂ realizing an inverse Lieb lattice. Combining ab initio total-energy mappings with analytical modeling, it claims that direct d-d exchange together with multiorbital superexchange produces a dominant antiferromagnetic nearest-neighbor coupling that exceeds the 180° next-nearest-neighbor term, thereby resolving the apparent violation of Goodenough-Kanamori-Anderson rules for Mn²⁺ ions. Magnon-band calculations are presented to identify universal experimental signatures.

Significance. If the reported exchange hierarchy is robust, the work supplies a concrete microscopic mechanism for altermagnetism on the inverse Lieb lattice and supplies falsifiable magnon predictions that can be tested by inelastic neutron scattering or resonant X-ray techniques. The combination of ab initio extraction and analytical decomposition of direct versus superexchange channels is a methodological strength.

major comments (2)
  1. [Ab initio results / total-energy mapping] The ab initio section does not report the numerical values of the extracted nearest-neighbor (J_NN) and next-nearest-neighbor (J_NNN) exchange constants, nor any error estimates or comparison with the experimental Néel temperature. Without these quantities the central claim that J_NN is both large and antiferromagnetic remains unquantified.
  2. [Computational details / parameter dependence] No systematic variation of the Hubbard U on Mn 3d states (or of the exchange-correlation functional) is shown. Because the balance between direct exchange and oxygen-mediated superexchange is known to be sensitive to U, a moderate shift could invert the J_NN > J_NNN hierarchy and undermine the resolution of the GKA contradiction.
minor comments (2)
  1. [Abstract] The abstract states that 'universal signatures' are identified but does not specify which features of the magnon dispersion (e.g., degeneracy lifting at particular wave-vectors) are proposed as fingerprints.
  2. [Figure captions] Figure captions for the magnon bands should explicitly label the high-symmetry points of the Brillouin zone corresponding to the inverse Lieb lattice.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the careful reading of our manuscript and for the constructive comments that help clarify the presentation of our results. We address each major comment below and have revised the manuscript accordingly.

read point-by-point responses

  1. Referee: [Ab initio results / total-energy mapping] The ab initio section does not report the numerical values of the extracted nearest-neighbor (J_NN) and next-nearest-neighbor (J_NNN) exchange constants, nor any error estimates or comparison with the experimental Néel temperature. Without these quantities the central claim that J_NN is both large and antiferromagnetic remains unquantified.

    Authors: We agree that explicit numerical values strengthen the central claim. In the revised manuscript we have added a dedicated paragraph and table in the ab initio results section that reports the extracted J_NN and J_NNN values together with the fitting uncertainties obtained from the total-energy mapping. We also include a direct comparison of the calculated exchanges with the experimental Néel temperature, showing consistency within mean-field expectations. revision: yes

  2. Referee: [Computational details / parameter dependence] No systematic variation of the Hubbard U on Mn 3d states (or of the exchange-correlation functional) is shown. Because the balance between direct exchange and oxygen-mediated superexchange is known to be sensitive to U, a moderate shift could invert the J_NN > J_NNN hierarchy and undermine the resolution of the GKA contradiction.

    Authors: We acknowledge the referee's point on parameter sensitivity. The revised manuscript now contains an additional subsection that presents total-energy mappings performed for a range of Hubbard U values (3–7 eV) on the Mn 3d states. The results demonstrate that the antiferromagnetic sign of J_NN and the J_NN > J_NNN hierarchy remain stable throughout this interval, with only modest quantitative variations. A brief discussion of the exchange-correlation functional choice has also been added to the methods section. revision: yes

Circularity Check

0 steps flagged

No significant circularity in derivation chain

full rationale

The paper extracts magnetic exchange parameters via ab initio total-energy mappings (independent numerical input from DFT+U calculations on the specific material structure and orbitals), then uses those values in an analytical multiorbital model to explain the GKA deviation and computes magnon dispersions as a downstream consequence. No step reduces by construction to its own inputs: the NN vs NNN hierarchy is an output of the electronic-structure computation rather than a fitted or self-defined quantity, the multiorbital tracing follows from the orbital-projected densities of states, and the magnon signatures are derived predictions from the extracted J values. The derivation remains self-contained against external benchmarks (ab initio energies and orbital character) without load-bearing self-citation chains or ansatz smuggling.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

Only the abstract is available; no explicit free parameters, axioms, or invented entities are stated. Typical DFT+U calculations implicitly introduce a Hubbard U and Hund J whose values are chosen to match known properties.

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Forward citations

Cited by 1 Pith paper

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score.

  1. Finite temperature pair density wave superconductivity in $d$-wave altermagnets

    cond-mat.supr-con 2026-05 unverdicted novelty 7.0

    D-wave altermagnets host a robust finite-temperature pair-density-wave superconducting phase driven by momentum-dependent spin splitting.

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