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Carbon doped into Bi2Se3 as substitution for Se was reported inducing simultaneous magnetic and hole doping. In this work, based on theoretical and experimental approaches, we find that carbon doped Bi2Se3 is indeed spin polarized, while the magnetic moments are small and hole doping is little. Most carbon atoms energetically favor to be dimer- and trimer-substitutions for Se which induce neither magnetism nor charge doping. A few isolated carbon atoms doped at interstitial sites in the vdW gap or at Se vacancies result in spontaneous spin polarization and charge doping. The diffusion of a single carbon dopant into Bi2Se3 is difficult, while if dopants are close, carbon clusters can easily form, which means that the isolated, pairwise, and trimeric carbon dopants should coexist. These studies suggest that to obtain strong ferromagnetic C-Bi2Se3, experiments need careful design to dope single carbon atoms into bulk dispersedly. [ABSTRACT FROM AUTHOR]

Carbon doped into Bi2Se3 as substitution for Se was reported inducing simultaneous magnetic and hole doping. In this work, based on theoretical and experimental approaches, we find that carbon doped Bi2Se3 is indeed spin polarized, while the magnetic moments are small and hole doping is little. Most carbon atoms energetically favor to be dimer- and trimer-substitutions for Se which induce neither magnetism nor charge doping. A few isolated carbon atoms doped at interstitial sites in the vdW gap or at Se vacancies result in spontaneous spin polarization and charge doping. The diffusion of a single carbon dopant into Bi2Se3 is difficult, while if dopants are close, carbon clusters can easily form, which means that the isolated, pairwise, and trimeric carbon dopants should coexist. These studies suggest that to obtain strong ferromagnetic C-Bi2Se3, experiments need careful design to dope single carbon atoms into bulk dispersedly. [ABSTRACT FROM AUTHOR]

[Display omitted] • The spin states of TMN 4 -G (TM = Mn, Fe and Co) transfer between low- and high-spin states at critical strains. • Spin polarization turn up in nonmagnetic ScN 4 - and NiN 4 -G, and turn off in magnetic CuN 4 -G under certain strains. • The origin of the spin-state transitions is related with the TM valance electrons and charge transferred. Spin-tunable materials are very appealing for applications in multifunctional spintronics devices because of their ability to switch between different spin states with external stimuli such as strain, light or electric-field, etc. As a promising material for spintronics, transition-metal-nitrogen-carbon (TM-N-C) materials have achieved considerable attentions. Based on density functional calculations, we systematically investigate the magnetic properties of four-nitrogen coordinated transition-metal embedded graphene (TMN 4 -G, TM = all 3 d -elements). The embedded configurations of TMN 4 -G show rich tunable spin states by external strains, exhibiting two kinds of spin-state transitions: 1) Spin crossover between low- to high-spin states (TMN 4 -G, TM = Mn, Fe and Co); 2) Spin polarization turned up or turned off in nonmagnetic systems (ScN 4 -G and NiN 4 -G) or in magnetic CuN 4 -G, respectively. The spin-state transitions occur abruptly for systems with magnetic TM elements, while continuously for those with nonmagnetic elements. The origin of the spin-state transitions is explored and found related with the TM valance electrons and charge transferred. Our findings could open an avenue for the efficient tuning of spin and magnetism in graphene based TMN 4 structures for application in spintronics. [ABSTRACT FROM AUTHOR]

Magnetic moments of a (4 × 4) F-Tetra-MoN 2 with biaxial tensile strains (marked in violet), and with the same strains while doped extra hole of 1.0 × 1014 cm−2 concentration (marked in olive). Structures of F-Tetra-MoN 2 (F atom is chemically adsorbed at the bridge site between two Mo atoms). • Fluorination introduce rich magnetic behaviors into the Tetra- MoN 2 (F-Tetra-MoN 2). • Biaxial strains and charge doping result in manipulation of spin polarization in F-Tetra-MoN 2. • Coverage of F adsorbates causes dramatic change of the magnetic properties. So far the Tetra-MoN 2 has been reported as the most stable structure of MoN 2 , which is a nonmagnetic semiconductor with an indirect band gap. With fluorine atoms adsorbed on the surface, the fluorinated Tetra-MoN 2 (F-Tetra-MoN 2) exhibits rich magnetic behaviors mediated by the polarized p electron of N and induced by small strains and low-concentration charge doping. Coverage or distance of F adsorbates also causes dramatic change of the magnetic properties. F adsorbates trend to aggregation which induces stronger spin polarization in F-Tetra-MoN 2. These results suggest an efficient route to tune the magnetic properties of fluorinated Tetra-MoN 2. [ABSTRACT FROM AUTHOR]