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By employing nonequilibrium Green’s function methods in combination with density functional theory, we investigate electronic structures and transport properties of the armchair graphene nanoribbon (AGNR) heterojunctions consisting of the sulfur(S)-doped AGNR and the pristine one, which are realizable in experiments. The results show that such heterojunctions own inherent rectifying behaviour with a high rectifying ratio up to 10 4 , and the rectifying direction is totally controllable by choosing the width of ribbon. It is revealed that the rectifying mechanism is driven by easily pinning valence-band maximum (VBM) on the conduction band minimum (CBM) under forward biases but hardly pinning under reverse biases, and the rectifying direction is described by the interrelationship of the band gap between the S-doped AGNR and AGNR segments. Our findings provide a route for the design of AGNR-based rectifiers with controllable direction in molectronics.

Based on first-principles spin-polarized density functional theory calculations, the electronic structures, and magnetic properties of Cu and Zn-doped BiFeO 3 are investigated. The calculated formation energies show that Cu prefers to occupy Fe site, while the Zn prefer to occupy Bi site. All the doped BiFeO 3 systems turn out to be favorable for G-type antiferromagnetic arrangement. The substitution of Cu and Zn for Fe produces a magnetic moment of 3.0 and 4.0 μ B per dopant, respectively. The net magnetic moments are from the broken symmetry of the AFM spin ordering network. For the substitution of Cu and Zn for Bi, the net magnetic moment originates from Cu/Zn itself and hole introduced by Cu/Zn. Two-Cu/Zn-doped cases show various magnetic behaves. If O vacancy is far away from dopants, the O vacancies don't affect the net magnetic moment of the substitution of Cu and Zn for Fe, but have notable effect for Bi site doping. The O vacancies result in metallicity in all doped cases. Our study demonstrates that the nonmagnetic Cu and Zn doping will lead to the diversity and complexity of magnetic properties depending on doping sites, distance between dopants, intrinsic defect, and so on, which could be responsible for the observed various magnetic behaviors in Cu/Zn-doped BiFeO 3 samples.

The structural, electronic, and magnetic properties of the two-dimensional (2D) AlN nanosheet doped with nonmagnetic (NM) atoms X(=Li, Na, and K) are investigated by first principle calculations. We find that the X atoms lie out of the 2D AlN nanosheet, while the structures are metastable when the dopants are situated in the plane of the nanosheets. The total magnetic moments induced by doping are 2.0μB per supercell which mainly originated from the spin-polarized holes localized on the three N atoms surrounding the dopant for all the doped AlN nanosheets. The substitution results in deep p-type acceptor levels which consist of the unoccupied N-2p orbitals. Magnetic coupling calculations demonstrate that FM states are energetically favorable when two X atoms are far away from each other while anti-ferromagnetic states are energetically favorable when two X atoms adjoin in the crystal lattice. Remarkably, calculations show that K-doped AlN nanosheet has room temperature ferromagnetism within fairly low concentration (of 5.56% doping).

Searching for low-dimensional materials with high Curie temperature and full spin–polarization ratio is an urgent demand for the rapidly evolving spintronic industry. Here, the stability, electronic structures, and magnetic properties of two-dimensional hexagonal CrOX (X = F, Cl, Br) monolayers were investigated with density functional theory. The CrOF and CrOCl monolayers exhibit good stability and are ferromagnetic semiconductors with a Curie temperature of ~ 215 and 64 K, respectively, as determined from Monte Carlo simulations. High-temperature ferromagnetism and controllable half-metallicity can be realized by hole doping from a gate voltage. At a doping concentration of 0.1|e|per unit cell, the Curie temperatures of CrOF and CrOCl are increased to 385 and 576 K, respectively, and the doped systems change from semiconductors into half-metals. These findings suggest a route for controlling and tuning the electronic and magnetic properties of CrOX monolayers, which are promising materials for spintronic devices.

2D materials with robust half-metallicity have received attention due to their potential applications in nanospintronic devices. Using density functional theory calculations and Monte Carlo (MC) simulation, we investigate the electronic structure and magnetism of CrI3 monolayer with embedded Ti atoms on its hollow sites. Ti implantation increases the magnetic moment from 6.0 μB to 10 μB per unit cell and renders the CrI3 monolayer half-metallic. MC simulation based on the Ising model reveals that the estimated Curie temperature (TC) of the Ti-modified CrI3 system is up to 282 K, which is larger than the 45 K for unmodified CrI3. The enhanced TC, half-metallicity, and strengthened magnetization imply that the 2D CrI3 monolayer make a big step toward practical spintronic applications.

Based on first-principles spin-polarized density functional theory calculations, the relative stability, electronic structures, and magnetic properties of B-, C-, N-, and F-doped BiFeO3 are investigated. The substitution of B, C, N, and F for O produces a magnetic moment of 3.0, 2.0, 1.0, and 1.0 μB per dopant, respectively. The net magnetic moments are from the broken of the symmetry of the AFM spin ordering network. We find that the BiFeO3 with one O atom substituted by a C atom leads to a ferrimagnetic half-metallic property with a C-type spin alignment. The B- and N-doped BiFeO3 are ferrimagnetic semiconductors, and ordered an A-type and a G-type spin alignment, respectively. As for F-doped case, system becomes metallic in its G-type spin alignment. Our study demonstrates that the nonmagnetic elements doping is an efficient route to tune magnetic and electronic properties in BiFeO3.

Basing on ab initio calculations, we investigate the electronic structures and magnetic properties of triazine-based graphitic carbon nitride (gt-C3N4) sheets with adsorbed by Nb and Tc. Both Nb and Tc atoms energetically prefer to be adsorbed on the cavity site. Adsorptions lead to total magnetic moments of 1.00 μB per Nb or Tc atom. The magnetic moments on Nb anti-ferromagnetically couples with those on C and N atoms, but the spins between Nb atoms strongly ferromagneticially couple to each other. The system therefore becomes ferromagnetic (FM) semiconductor with reduced band-gap, and the estimated Curie temperature (TC) is much higher than room temperature. The magnetic moments of Tc adsorbed system ferromagnetically couple with each other. The adsorption of Tc atom changes the semiconducting gt-C3N4 into half metallic material. These findings indicate adsorptions of Nb/Tc lead to various magnetic characters that has potential application in future spintronics.