Magnetic and Electrochemical Properties of the Altermagnetic Layered Antiperovskite Na2Mn2OS2

Incorporating multiple anions into perovskite-type frameworks provides a handle to design innovative lattices and trigger exotic properties. Inverse Lieb lattices have been receiving substantial interest as hosts for d-wave altermagnetism. One mixed-anion system in which these lattices have been experimentally realized is layered oxychalcogenides. By employing a high-pressure, high-temperature synthesis method, we introduce Na2Mn2OS2 as an additional member of this family of compounds. Na2Mn2OS2 adopts an antiperovskite-derived structure, consisting of layers of face-sharing MnO2S4 octahedra. Magnetization and neutron diffraction data reveal that the phase undergoes magnetic ordering below 144 K. The low-temperature magnetic structure has zero net magnetization and is invariant under a combination of rotation and time reversal, thereby fulfilling the symmetry criteria to be considered as an altermagnet candidate. Electronic band structure calculations demonstrate that the phase contains spin-polarized bands, providing further evidence that Na2Mn2OS2 can be described as an altermagnet. An electrochemical investigation of this compound was performed, aiming both to tailor the physicochemical properties of the material through desodiation and to yield a possible Na-ion cathode material. While there are indications of Na-deintercalation, the charge compensation mechanism appears to involve irreversible sulfur oxidation rather than manganese oxidation, thus preventing the application of Na2Mn2OS2 as a positive electrode for Na-ion batteries.