Magnetic couplings and applied electric field regulation in diradical SiC defect diamond-like nanoclusters

Abstract

The electronic properties and their modulations for various defect nanoscale diamonds and their analogues are currently of profound interest due to their potential applications. However, their intriguing electronic properties and relevant phenomena are still poorly understood. In this work, using the density functional theory method, we computationally investigate the magnetic coupling characteristics of SiC nanoclusters with four different types of defect center (NVe, NNV, NBV and BBV). Our results reveal that three main modifications, surface perfluorination, layer expansion and doping by N or B, can each regulate the spacing and electronic interaction in the radicals and thus determine whether they involve ferromagnetic or antiferromagnetic coupling. The magnetic coupling essentially originates from the magnetic moments produced by the p-orbital on C-radicals around the Si vacancy. In particular, an applied electric field can affect the distribution and stability of an excess electron among the C-radicals. Detailed analyses uncover two important relationships, J ∝ I (field intensity, I) and J ∝ d (diradical spacing, d), which can better describe the dependence of the magnetic coupling constant J on non-intuitive variables. When an excess electron becomes localized at one of three C-radicals from the delocalized distribution over three C-radicals, the other two C-radicals can switch from strong FM coupling to weak AFM coupling. This phenomenon can be well accounted for by the transfer, transition and transformation of the corresponding electron. Interestingly, two highest singly occupied molecular orbitals in the α- and β-orbitals in the BS state do not contribute to the total spin density distribution; instead two next highest ones do. This work provides new insights into electron spin couplings for endohedrally confined multiple radicals and possible magnetic characteristics in such SiC defect diamond analogues and also provides helpful information for the design of inorganic magnetic materials and logic devices.