Electric field manipulated magnetic spin coupling properties in lithium-trapped nitrogen-vacancy nanodiamonds

Abstract

The nitrogen-vacancy (NV) defect center in diamonds is highly promising for various applications, including quantum state engineering and magnetic sensing, particularly when doped with heteroatoms. Lithium can be readily incorporated into the NV center (NVLi), where it donates an active electron to form a lithium cation. However, the intrinsic electronic characteristics of the NVLi center in diamonds, particularly the spin coupling among carbon radicals and their response to external electric fields (EFs), remain poorly understood. Here, we employ DFT calculations to firstly investigate the magnetic coupling behavior of carbon radicals in the NVLi center and their response to EFs. Our results demonstrate that the NVLi center exhibits ferromagnetic (FM) spin coupling, and the FM spin coupling strength varies significantly (from 2078.54 cm⁻¹ to 470.14 cm⁻¹) with increasing EF intensity along the C⋯Li axis, while remaining stable along the N⋯Li axis. The study indicates that an EF along the C⋯Li causes a redistribution of electrons and a decrease in the structure symmetry of the clusters. In particular, the EF along the C⋯Li axis alters the molecular orbital distribution through Coulomb forces, modifying the interaction of the singly occupied molecular orbitals and thereby regulating the magnetism, whereas the EF along the N⋯Li axis minimally impacts the symmetry of the NVLi nanocluster. This work provides insights into the spin coupling properties of such defective materials and their regulation mechanism by EFs, especially the change in orbital interaction, and also provides inspiration for the design of logic devices such as internally doped and co-doped inorganic magnetic materials.