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In this paper, first-principle calculation methods based on density functional theory are used to study the electronic structure of arsenic nitride nanoribbons (AsNNR), arsenic nitride nanoribbons passivated by hydrogen at the edges (HAsNNR), and arsenic nitride nanoribbons oxidized at the edges (OAsNNR). The results show that the spin-polarized nanoribbons are energy favorable than the non-spin-polarized nanoribbons. The zigzag type OAsNNR exhibits ferromagnetic (FM) half-metallic state. The non-equilibrium Green’s function is used to study spin-polarized current of OAsNNR, and the full spin-polarized current is obtained by calculation.

We investigate the electronic structure and magnetic properties of layered compound Sr3Fe2O5 based on first-principles calculations in the framework of density functional theory with GGA+U method. Under high pressure, the ladder-type layered structure of Sr3Fe2O5 is transformed into the infinite layered structure accompanied by a transition from G-type anti-ferromagnetic (AFM) insulator to ferromagnetic (FM) metal and a spin transition from S = 2 to S = 1. We reproduce these transformations in our calculations and give a clear physical interpretation.

We investigate the electronic structure and magnetic properties of layered compounds SrBO 2 (B = Co, Ni, Mn) based on first principles calculations in the framework of density functional theory with GGA+ U method. We compute the phonon dispersion of these compounds to probe the dynamical stability and find that all the compounds are dynamically stable. SrCoO 2 and SrNiO 2 are G-type antiferromagnetic insulators, and SrMnO 2 is an A-type antiferromagnetic conductor. The electronic configurations of 3d orbitals are (d xz ) 2 (d z 2 ) 2 ( d yz ) 1 (d xy ) 1 (d x 2 - y 2 ) 1 and (d xz ) 2 (dy z ) 2 (d z 2 ) 2 (d xy ) 1 (d x 2 - y 2 ) 1 in SrCoO 2 and SrNiO 2 , respectively. SrCoO 2 shows a Jahn-Teller distortion ( a > b ) because the down-spin Co 3d electron occupies the degenerate (d xz , d yz ) levels. Using Monte Carlo simulations based on the Heisenberg model with exchange parameters obtained from first principles calculations, we obtain the Neel temperatures ( T N ) of SrCoO 2 and SrNiO 2 , which are 249 K and 85 K, respectively.

We study the electronic structures and magnetism of SrFe 0.5 Ru 0.5 O 2 by first-principles calculations in the framework of density functional theory (DFT) with generalized gradient approximation plus on site repulsion (GGA+ U ). The DFT calculations were carried out with ten kinds of Fe-site doping form. Calculations show that the d-orbital electronic configurations of Fe 2+ and Ru 2+ ions are ( d z 2 ) 2 ( d yz d xz ) 2 ( d xy ) 2 ( d x 2 − y 2 ) 1 and ( d z 2 ) 2 ( d yz d xz ) 3 ( d xy ) 1 ( d x 2 − y 2 ) , respectively, which are independent of the doping form. The degenerated ( d xz d yz ) orbitals of Ru 2+ ions are occupied by three electrons, so it gives rise to the Jahn–Teller distortion. The calculated magnetic moments of Fe 2+ and Ru 2+ ions are 3.7 μ B and 1.6 μ B , respectively. The exchange parameters including nearest neighbor (NN) ions and next nearest neighbor (NNN) ions are calculated by using Heisenberg model and the magnetic frustration in the ordered structure is explained by the competition of the exchange parameters. We also study the external pressure effect on the compound. A pressure-induced orthorhombic to tetragonal structure transition accompanied by an insulator to half-metal transition and an antiferromagnetic (or spin glass) to ferromagnetic state transition is observed.

We investigate the electronic structure and magnetic properties of SrFe 1− x Mn x O 2 system using first-principles calculations and the site-random Heisenberg model. Calculations show that the ground state of SrFe 1− x Mn x O 2 with x ≤0.3 is a Mott insulator. The ground state of SrFe 0.875 Mn 0.125 O 2 has the same (πππ) ordered antiferromagnetic state as in the undoped compound. For SrFe 0.75 Mn 0.25 O 2 , the (πππ) as well as the (ππ0) ordered antiferromagnetic state may exist depending on the atomic configuration. The magnetic structure and its change by doping can be explained based on the estimated interlayer exchange interactions. The effects due to random distributions of Fe and Mn ions are investigated by Monte Carlo simulations based on the site-random Heisenberg model with exchange parameters obtained from first principles calculations. The results show that the Neel temperature T N corresponding to the phase transition from the paramagnetic phase to the (πππ) ordered phase decreases with increasing x , and a second transition from the (πππ) ordered phase to a mixed phase with coexistence of both the (πππ) and (ππ0) orderings develops at T N ′ below T N .

We investigate the electronic structures and electronic transport properties of zigzag phosphorene nanoribbons with oxygen-saturated edges (O-zPNRs) by using the spin-polarized density functional theory and the nonequilibrium Green's function method. The results show that the O-zPNR is an antiferromagnetic (AFM) or ferromagnetic (FM) semiconductor with spins localized at two ribbon edges anti-parallel or parallel with each other. The electronic transmission for the single AFM or FM O-zPNR is zero when a bias voltage is applied to the two electrodes made of the same type O-zPNR. Nonzero transmission arises for the AFM-AFM and FM-FM O-zPNR heterojunctions. The transmission spectrum and the electrical current are fully spin polarized for the FM-FM O-zPNR heterojunction. An in-plane transverse electrical field can effectively manipulate the electronic structure and spin-dependent electronic transport. It induces splitting of the spins of the two edges and makes the AFM O-zPNR become a half metal. Moreover, the transverse electrical field gives rise to the transmission spectrum and the spin polarized electrical current for the AFM-AFM O-zPNR heterojunction. The degree of spin polarization can be tuned by the strength of the transverse field.

Two-dimensional (2D) half-metallic materials are essential to develop next-generation spintronic devices. Moreover, electrical controllability and room-temperature magnetism are two important ingredients for applications in spintronics. Here, we report findings of a combination of these properties in 2D honeycomb structures of group-V $\mathrm{N}X$ ($X$=N, P, As, Sb, Bi) binary compounds from first-principles calculations. These novel 2D materials are stable semiconductors with indirect band gaps. Hole doping can induce magnetism due to their Mexican-hat band edges and make them half-metals. Some of these half-metals exhibit inverse spin-polarization direction when changing the doping level, which can be achieved by changing the external voltage gate. Monte Carlo simulations based on the Ising model suggest the Curie temperatures of these half-metals are much higher than room temperature. These outstanding properties make monolayer $\mathrm{N}X$ promising candidates for spintronic applications.

We present first-principles calculations of electronic structures of a class of two-dimensional (2D) honeycomb structures of group-V binary compounds. Our results show these new 2D materials are stable semiconductors with direct or indirect band gaps. The band gap can be tuned by applying lattice strain. During their stretchable regime, they all exhibit metal-indirect gap semiconductor-direct gap semiconductor-topological insulator (TI) transitions with increasing strain from negative (compressive) to positive (tensile) values. The topological phase transition results from the band inversion at $\Gamma$ point due to lattice strain and is irrelevant to spin-orbit coupling (SOC)., Comment: 16 pages, 6 figures

We have studied the electronic structures and magnetism of SrFeO2 under pressure by first-principles calculations in the framework of density functional theory (DFT) with GGA+U and HSE06 hybrid functionals, respectively. The pressure-induced spin transition from S = 2 to S = 1 and the antiferromagnetic-ferromagnetic (AFM-FM) transition observed in experiment are well reproduced by taking the site repulsion U and its pressure dependence into account. The electronic structure and its change with the pressure can be qualitatively understood in an ionic model together with the hybridization effects between the Fe 3d and O 2p states. It is found that the pressure leads to a change in Fe 3d electronic configuration from (d(z(2)))(2)(d(xz)d(yz))(2)(d(xy))(1)(d(x(2)-y(2)))(1) under ambient conditions to (d(z(2)))(2)(d(xz)d(yz))(3)(d(xy))(1)(d(x(2)-y(2)))(0) at high pressure. As a result, the spin state transits from S = 2 to S = 1 and both the antiferromagnetic intralayer Fe-O-Fe superexchange interaction and the interlayer Fe-Fe direction exchange coupling at ambient pressure become ferromagnetic at high pressure according to the Goodenough-Kanamori (G-K) rules. Additionally, our calculations predict another spin transition from S = 1 to S = 0 at pressures of about 220 GPa.

The electronic properties of two-dimensional puckered arsenene have been investigated using first-principles calculations. The effective mass of electrons exhibits highly anisotropic dispersion in intrinsic puckered arsenene. Futhermore, we find that out-of-plane strain is effective in tuning the band gap, as the material undergoes the transition into a metal from an indirect gap semiconductor. Remarkably, we observe the emergence of Dirac-like cone with in-plane strain. Strain modulates not only the band gap of monolayer arsenene, but also the effective mass. Our results present possibilities for engineering the electronic properties of two-dimensional puckered arsenene and pave a way for tuning carrier mobility of future electronic devices.