Electron-Coupled Proton Transfer Governed Magnetic Spin Couplings and Switching in Defect Nano Silicon Carbide

The formation mechanism, defect characterization, and potential applications of the Si vacancy (VSi) with internal H atoms in the silicon carbide (SiC) materials have been widely investigated. However, the inherent electronic properties and related phenomena induced by internal H dynamics in VSi, especially the C-radical spin interaction dynamics, are still poorly understood in such nano SiC. In this work, using the density functional calculations, we explore the magnetic coupling characteristics and dynamic behaviors induced by H-motion in nano SiC with four different types of H-doped VSi defect centers, (VSi + H)-, (VSi + H)+, (VSi + 2H), and NVH [i.e., (NCVSi + H)0 in which one of C-radical sites in VSi is replaced by N]. Our results reveal their unique ferromagnetic (FM) or antiferromagnetic (AFM) spin coupling characteristics and H-motion -induced interconversion. In general, the internal H-motion goes through the electron-coupled proton transfer (ECPT) in a C-H center dot center dot center dot C unit which has great impact on molecular orbitals, spin densities, and thus spin couplings among the C-radicals, allowing the VSi center to undergo magnetic switching between FM and AFM coupling. Interestingly, as in the (VSi + H)- center, such ECPT can further drive the excess electron delocalized on three C-radicals to gather at the ECPT unit, forming a three-center-four-electron (3c-4e) [C center dot center dot center dot H center dot center dot center dot C]- covalent H-bond with the switching of magnetic coupling. This work provides the dynamics insights into the spin coupling characteristics and its regulation by internal H-motion and multiple radical characters of such defect materials and the formation of a 3c-4e H-bond assisted by excess electron, and also provides inspired information for the design of inorganic magnetic materials and logic devices which can be controlled by interior doping and dopant dynamics.