Importance of the indirect exchange interaction via s states in altermagnetic HgMnO3

The electronic and magnetic properties of a recently synthesized perovskite phase of ${\mathrm{HgMnO}}_{3}$ are studied. By means of ab initio density functional theory calculations this material was shown to be altermagnetic. We discuss the features of its electronic structure and unveil the physical mechanism of the anomalous suppression of the antiferromagnetic exchange interaction in this material. While it is tempting to ascribe the unexpectedly weak exchange interaction between nearest neighbors to crystal structure distortions, this is an indirect ferromagnetic exchange via Hg $6s$ states, which strongly affects the magnetic properties. This effect can be important not only for ${\mathrm{HgMnO}}_{3}$, but also for many other transition metal compounds having empty $s$ states, placed not far above the Fermi level.