Mott transition and superexchange mechanism in magnetically doped X Si2N4 caused by large 3 d orbital onsite Coulomb interaction

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, MoSi₂N₄ , has been prepared, attracting public attention to the X_{A 2}Z₄ series of materials. Naturally, doping with 3 d 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 3 d orbitals which is strongly related to the Mott transition and therefore causes the superexchange interaction.