- Nano Idea
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Metal-Free Half-Metallicity in B-Doped gh-C3N4 Systems
© The Author(s). 2018
- Received: 19 December 2017
- Accepted: 9 February 2018
- Published: 20 February 2018
Half-metallicity rising from the s/p electrons has been one of the hot topics in spintronics. Based on the first-principles of calculation, we explore the magnetic properties of the B-doped graphitic heptazine carbon nitride (gh-C3N4) system. Ferromagnetism is observed in the B-doped gh-C3N4 system. Interestingly, its ground state phase (BC1@gh-C3N4) presents a strong half-metal property. Furthermore, the half-metallicity in BC1@gh-C3N4 can sustain up to 5% compressive strain and 1.5% tensile strain. It will lose its half-metallicity, however, when the doping concentration is below 6.25%. Our results show that such a metal-free half-metallic system has promising spintronic applications.
- Doped gh-C3N4
- Strain effects
- First-principles methods
Spintronic devices simultaneously utilize the charge and spin freedom of electrons and have attracted increasing attentions due to their potential use in logic and memory devices [1, 2]. Their performances, however, heavily depends on the spin polarization ratio of currents. There is a pressing need for materials that can generate 100% spin-polarized currents, therefore. Half-metal materials, which can do this at Fermi level E F , are considered as the ideal materials for spintronic devices [3–6]. Many half-metallic ferromagnets, such as doped manganites , double perovskites , and Heusler compounds [9, 10], have attracted extensive attentions in recent years. However, these half-metallic materials usually contain transition-metal (TM) and have strong spin-orbit coupling strengths, which result in short spin relaxation times. It is necessary to develop advanced TM-free half-metallic materials with long spin relaxation time, therefore.
Two-dimensional (2D) atomic crystals with planar surfaces have attracted a lot of attentions recently due to their potential application in spintronic devices [11–24]. Graphene and its several 2D analogues, such as hexagonal boron nitride and carbon nitride, have great potential for spintronics because of their exceptional properties, e.g., low dimensionality and electron confinement. Although most of these materials are non-magnetic in nature, there are many ways, such as doping and strain to reach the half-metallic ferromagnetism. For example, B, Al, and Cu embedded trizaine-based g-C3N4 (gt-C3N4) have been reported to be half-metallic . The graphene-like carbon nitride also presents half-metallicity under tensile strain . In addition, the heptazine-based g-C3N4 (gh-C3N4) has received a lot of attentions [25–33].
A large number of research works have investigated the electronic and magnetic properties of transition metal incorporated gh-C3N4 systems [11, 28, 30]. These transition metal embedded gh-C3N4 materials have been synthesized at elevated temperature [34–39]. Theoretical works show that the transition metals can bind more strongly with gh-C3N4 than with graphene and these systems are metallic . Indrani et al. have systematically investigated the magnetic properties of C-dope gh-C3N4 systems by density functional theory (DFT) calculations . They found that all of these C-dope gh-C3N4 systems are ferromagnetism, and a high energy phase shows strong half-metallicity and 400 K Curie temperature. Recently, Gao et al.  have experimentally demonstrated the capacity to fabricate the B-doped gh-C3N4 nanosheets, which present high-temperature ferromagnetism and half-metallicity. Despite of these early works, a systematic theoretical investigation of the B-doped gh-C3N4 is missing. Some fundamental issues such as the effects of doping position and B concentration on the electronic and magnetic properties of gh-C3N4 await clarification. Moreover, the effects of strain also need investigation.
In this work, we systematically investigate the effects of doping positions, B concentrations, and strain on the electronic and magnetic properties of the B-doped gh-C3N4 system through first-principles calculations. The results show that strong half-metallicity can be found in the ground state of B-doped gh-C3N4 (BC1@gh-C3N4). Not only doping positions but also doping concentrations play important roles in inducing half-metallicity. Moreover, the half-metallicity in BC1@gh-C3N4 can sustain up to 5% compressive strain and 1.5% tensile strain. The B-doped gh-C3N4 systems are promising for spintronics, therefore.
A tetragonal unit cell containing 28 atoms of gh-C3N4 (corresponding to 8.333% doping concentration) is employed to simulate the B-doped gh-C3N4 system as shown in Fig. 1b (the red dashed line). After considering early report  that the substitution on the C sites (C1 and C2) is more favorable than on the N sites (N1, N2, and N3), only the configurations of B substituting C have been investigated to explore their magnetic properties. As a result, the two different B-doped gh-C3N4 isomers (BC1@gh-C3N4 and BC2@gh-C3N4) are studied. The fully relaxed structures of BC1@gh-C3N4 and BC2@gh-C3N4 are given in Fig. 1c, d, respectively.
The calculated cohesive energies, formation energies, and magnetic moments for BC1@gh-C3N4 and BC2@gh-C3N4
Ecoh (eV per atom)
E f (eV per atom)
M (μ B per unit)
Based on density functional theory calculations, the B-doped gh-C3N4 systems have been investigated for potential applications in spintronic devices. Ferromagnetism is observed in all B-doped gh-C3N4 systems. Moreover, a strong half-metallicity is achieved only in the ground state phase, i.e., BC1@gh-C3N4, which results from a spin split of the non-bonding δ states of highly unsaturated 2-fold coordinated N2 atoms. The half-metallicity is lost for low B-doping concentrations. Thus, both selective doping and its concentration play an important role in inducing magnetism and half-metallicity. The half-metallicity in BC1@gh-C3N4 can sustain up to 5% compressive strain and 1.5% tensile strain. These results show that the B-doped gh-C3N4 systems could be a ferromagnetic half-metallic material for magnetic memory and spintronic devices.
The authors thank National Natural Science Foundation of China, China Postdoctoral Science Foundation, and the Six Talent Peaks Project of Jiangsu for financial support.
This work was supported by the National Natural Science Foundation of China (NSFC) (Grant No. 61674022) and the China Postdoctoral Science Foundation (2015M570428).
HY is the first author. HY and YL designed the calculations. HY carried out the calculations and characterizations. XJ, ZS, JF, and XY helped to prepare and correct the manuscript. All authors read and approved the final manuscript.
The authors declare that they have no competing interests.
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