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arXiv · 2506.21661

Microscopic origin of the magnetic interactions and their experimental signatures in altermagnetic La$_2$O$_3$Mn$_2$Se$_2$

Laura Garcia-Gassull·Aleksandar Razpopov·Panagiotis Peter Stavropoulos·Igor I Mazin·Roser Valentí
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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.

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Laura Garcia-Gassull, Aleksandar Razpopov, Panagiotis Peter Stavropoulos, Igor I Mazin, Roser Valentí. 2025-06-26. Microscopic origin of the magnetic interactions and their experimental signatures in altermagnetic La$_2$O$_3$Mn$_2$Se$_2$. https://doi.org/10.1038/s44306-025-00125-9

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