Mott transition and superexchange mechanism in magnetically doped XSi2N4 caused by large 3d orbital onsite Coulomb interaction

Abstract

Magnetic two-dimensional materials have great potential in the preparation of nanoelectronic and spintronic devices. Recently, a new two-dimensional material with no corresponding bulk-structure, ${\mathrm{MoSi}}_{2}{\mathrm{N}}_{4}$, has been prepared, attracting public attention to the ${XA}_{2}{Z}_{4}$ series of materials. Naturally, doping with $3d$ magnetic element will result in various magnetic orderings. In our work, we replaced the Mo element with different transition-metal elements whose property varies from magnetic to nonmagnetic and screened out a variety of two-dimensional exchange scenarios. Then, we provided an analysis that shows the existence of a huge on-site Coulomb interaction at $3d$ orbitals which is strongly related to the Mott transition and therefore causes the superexchange interaction.