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A few novel two-dimensional (2D) CrX2 (X = O, S, Se) binary compounds with high Curie temperature and magnetoelastic coupling are predicted based on first-principles calculations.

The exciton binding energy, mechanical properties, and lattice thermal conductivity of monolayer BiI

Theoretical calculations were performed to investigate the effect of isovalent substitution of Fe with Ga on the magnetic and ferroelectric properties in BiFeO3 doped with 16.6% and 8.3% Ga. Such substitution will break the G-type anti-ferromagnetic order and enhance the magnetism of BiFeO3 by forming a stable ferrimagnetic order. The doped system maintains robust spontaneous polarization that is sufficiently large for practical applications at room temperature. The findings explain experimentally observed magnetism. The coexistence of magnetism and ferroelectricity in the doped BiFeO3 render it a candidate material for application to information storage and spintronics devices.

In this paper, the plasmonic system composed of a Metal-Insulator-Metal (MIM) waveguide and dual asymmetric side-coupled U-shaped cavities is reported. It demonstrates that the strong coupling effect can lead to the opening of new transmission window. One of new peaks originates from the interference between the dual U-shaped cavities and bus waveguide, and the other is induced by the asymmetry of the structure, and each peak can be well tuned independently by changing the structural parameters of the U-shaped cavity. The effects of dielectric parameters on the transmission characteristics of the coupled system are also analysis, we find that the sensor sensitivity can reach 496 nm/RIU and a new sharp peak will exist in the short-wave region when dielectric parameter n = 1.2. By combining the magnetic field distributions, the internal physical mechanism is discussed. The proposed compact and simple plasmonic structure may have potential applications in nano-scale filter and other high density plasmonic integration circuits.

On the basis of density functional theory, we predicted that Janus CrTeI and CrSeBr monolayers possess highly energetic, dynamical, and mechanical stability. Due to noncentral symmetry, the two monolayers exhibit vertical piezoelectricity with large piezoelectric coefficients d31 (1.745 and 1.716 pm V−1 for CrBSe and CrTeI, respectively), which are larger than those of most materials in existence. Both systems are also ferromagnetic (FM) semiconductors, with Curie temperature (TC) higher than 550 K and large in-plane magnetic anisotropy energy. Superexchange interactions are responsible for high-temperature FM order. A semiconductor to half metal transition can be regulated by carrier doping, which can be carried out by gate voltages. Doped systems still retain the same FM order as pristine ones; in particular, hole doping enhances exchange coupling, thereby increasing TC. The combination of piezoelectricity, high TC, and controllable electronic structures and magnetic properties makes magnetic 2D Janus CrSeBr and CrTeI attractive materials for potential applications in nanoelectronics, electromechanics, and spintronics.

We performed a systematic study of the electronic structures and magnetic properties of SnS 2 monolayer doped with non-magnetic elements in groups IA, IIA and IIIA based on the first-principles methods. The doped systems exhibit half-metallic and metallic natures depending on the doping elements. The formation of magnetic moment is attributable to the cooperative effect of the Hund's rule coupling and hole concentration. The spin polarization can be stabilized and enhanced through confining the delocalized impurity states by biaxial tensile strain in hole-doped SnS 2 monolayer. Both the double-exchange and p-p exchange mechanisms are simultaneously responsible for the ferromagnetic ground state in those hole-doped materials. Our results demonstrate that spin polarization can be induced and controlled in SnS2 monolayers by non-magnetic doping and tensile strain.

Due to 100% spin polarization, half-metallic systems play a great role in the development of nanoscale spintronic devices. We conduct extensive calculations within spin-polarized density functional theory to design a newtpye two-dimensional Cr2O3 monolayer. The monolayer demonstrates robust stability as verified by formation energy, phonon spectrum, elastic constants, and molecular dynamics simulation. Each Cr2O3 unit cell gives rise to a total magnetic moment of 6.0 μB, mainly resulting from Cr sites due to the cooperation between crystal-field effect and Hund’s exchange. The monolayer is identified as a half-metallic ferromagnet with Curie temperature up to 460 K and 100% spin polarization. The super-exchange mechanism and direct exchange interaction are responsible for the ferromagnetic coupling. Moreover, the system shows large magnetic anisotropy with the easy axis in the basal plane. The excellent stability, half-metallicity, high Curie temperature, and magnetic anisotropy endow the monolayer with great potential in spintronic devices. This work provides a new pathway for designing ferromagnetic material with half-metallicity and high Curie temperature.

A new category of tubular nanostructures solely composed of selenium was explored by using the density functional theory. Similar to those in carbon nanotubes, the armchair and zigzag tube-like structures formed as a roll-up α-Se nanoribbon. The zigzag (n ≤ 16, 0) nanotubes exhibit decreasingly narrow direct band gap, and the armchair (n, n) possess decreasingly moderate indirect gap. The strain energy of nanotubes is inversely proportional to the second power of the nanotube diameter. With increasing tube diameter, an initial rise and consequent decrease occurred in the effective masses to the limit value of α-Se monolayer. The carrier mobility of nanotubes is comparable with that of its monolayer with orders of 103 and 102 cm2V−1s−1 for electron and hole, respectively. The optical absorption spectra of α-Se nanotubes exhibit high absorbance in energy window cover the entire visible light spectrum. Therefore, α-Se nanotubes hold great potential for future applications in high-performance optoelectronics.

Using first-principles calculations, we investigate the geometric structures, stabilities, electronic structures, and magnetic properties of three kinds of AsP monolayers: blue-phosphorene-like AsP (blue AsP), black-phosphorene-like AsP (black AsP) and puckered AsP. Stability analysis implies a high possibility of fabricating AsP monolayers in experiments. The blue AsP monolayer possesses the most stable structure with an indirect band-gap of 2.52 eV. The blue AsP system is also a good candidate for visible light photocatalytic decomposition of water. The black one is a semiconductor with a direct band gap of 1.53 eV at the Γ point. The puckered AsP monolayer shows the lowest stability and narrowest indirect band gap of 1.38 eV. Both the intrinsic defects of P and As vacancies result in half-metallicity and magnetic semiconductor for blue and black AsP monolayers, respectively. Our results provide useful information to obtain new two dimensional materials for water splitting photocatalysts and spintronic devices.

Auxetic materials, which possess a negative Poisson's ratio (NPR), have been a hot topic in materials science research. Through atomistic simulations, we theoretically rediscover a few novel two-dimensional (2D) VA-nitride (VA-N) binary compounds with δ-phosphorene-like structures. The structures in the δ-phase (except for δ-PN) exhibit better stability in terms of energy, thermodynamics, and mechanics with respect to their counterparts in the α- and β-phases. The structures in the δ-phase show semiconducting behaviors with direct band gaps falling in the visible light region. Interestingly, most structures in the α- and δ-phases (except for δ-BiN) exhibit large in-plane NPRs and excellent mechanical properties. The maximum NPR occurs along the zigzag (x) direction for the δ-phases and along the diagonal direction for the α-phases. Particularly, for α- and δ-SbN, the NPRs are −0.628 and −0.296, respectively. δ-SbN can sustain tensile strains of up to 22% and 35% with maximum stresses of 12.1 and 9.8 GPa in the zigzag and armchair directions, respectively. In addition, the transverse response can reach up to 6.6% at a strain of ∼18% along the armchair (y) direction for δ-SbN, which is considerably higher than those of other 2D auxetic materials. Our results reveal that 2D VA-N binary compounds have potential applications in designing 2D electromechanical and optoelectronic devices.

The exciton binding energy, mechanical properties, and lattice thermal conductivity of monolayer BiI3 are investigated on the basis of first principle calculation. The excitation energy of monolayer BiI3 is predicted to be 1.02 eV, which is larger than that of bulk BiI3 (0.224 eV). This condition is due to the reduced dielectric screening in systems. The monolayer can withstand biaxial tensile strain up to 30% with ideal tensile strength of 2.60 GPa. Compared with graphene and MoS2, BiI3 possesses superior flexibility and ductility due to its large Poisson’s ratio and smaller Young’s modulus by two orders of magnitude. The predicted lattice thermal conductivity k L of monolayer BiI3 is 0.247 W m−1 K−1 at room temperature, which is lower than most reported values for other 2D materials. Such ultralow k L results from the scattering between acoustic and optical phonon modes, heavy atomic mass, and relatively weak chemical bond.

First-principles calculations are performed to comparatively study the structural, electronic structures and magnetic properties of Mo doped AlN, GaN and InN monolayers (MLs). After Mo atom doping, the semiconducting GaN and InN MLs transform to metal, while the AlN ML keeps semiconducting with a reduced gap. Total magnetic moments of 1.0 and 0.54 µ B , which mainly arising from the localized Mo 4d states, are induced by doping in AlN and InN MLs, respectively, while the doped GaN ML is still nonmagnetic. Nevertheless, the excessive localization and strongly ionic character of the Mo-4d states in AlN ML directly impedes the magnetic coupling, leading to a paramagnetic ground states. A similar case is observed in Mo atoms doped InN ML. The firm N-Mo interaction prevent the impurity states permeating out the range of N-Mo pair, resulting in a quick vanishing of ferromagnetic coupling as the distance between two Mo atoms increasing. All configurations of Mo atoms doped GaN ML in this paper are room temperature ferromagnetic. Spin polarized itinerant electrons mediate the magnetic interaction between two Mo atoms. Increasing the Mo concentration may stabilize the FM state and produce a higher Curie temperature. Our calculations show that GaN nanosheets with Mo atoms doped may be a nice candidate for future spintronic devices. And we conclude that a appropriate magnitude of localization (or delocalization) is what the key point to produce room temperature ferromagnetism from this comparative study.

We investigate the electronic structures and magnetic properties of SnS2 monolayers substitutionally doped with 4-d transition-metal through systematic first principles calculations. The doped complexes exhibit interesting electronic and magnetic behaviors, depending on the interplay between crystal field splitting, Hund’s rule, and 4d levels. The system doped with Y is nonmagnetic metal. Both the Zr- and Pd-doped systems remain nonmagnetic semiconductors. Doping results in half-metallic states for Nb-, Ru-, Rh-, Ag, and Cd doped cases, and magnetic semiconductors for systems with Mo and Tc dopants. In particular, the Nb- and Mo-doped systems display long-ranged ferromagnetic ordering with Curie temperature above room temperature, which are primarily attributable to the double-exchange mechanism, and the p-d/p-p hybridizations, respectively. Moreover, The Mo-doped system has excellent energetic stability and flexible mechanical stability, and also possesses remarkable dynamic and thermal (500 K) stability. Our studies demonstrate that Nb- and Mo-doped SnS2 monolayers are promising candidates for preparing 2D diluted magnetic semiconductors, and hence will be a helpful clue for experimentalists.

We theoretically studied the structural, electronic, and magnetic properties in the two-dimensional (2D) AlN nanosheets (AlNNSs) doped with nonmagnetic (NM) atoms X(=Mg, Ca, Zn, and Sr), based on first-principles calculations. The structure relaxations show Mg and Zn atoms locate in the 2D AlNNS plane, while the Ca and Sr atoms lie out of it. The results based on GGA-PBE scheme show that all the doped AlN monolayers (ML) are half-metallic. Further, results within HSE06 scheme show that Mg-, Zn- and Sr-doped AlN ML remain half-metallic while Ca-doped case changes into magnetic semiconductor. Each dopant induces a total magnetic moment of 1.0 μB per supercell which mainly stemmed from the spin-polarized holes resided on the three nearest-neighboring N atoms. Calculations illustrate that ferromagnetic (FM) states are energetically stable when two X atoms separate far away from each other, while anti-ferromagnetic (AFM) states are energetically favorable when two X atoms locate at adjacent lattice sites. The long-range FM coupling and AFM one are attributed to the strong p-d/p-p interaction and the virtual hopping mechanism, respectively. Remarkably, because of the participation of the delocalized Zn-d orbitals in Zn-doped case, strong p-d/p-p interactions gain supremacy in the competition between virtual hopping mechanism and p-d/p-p interaction, resulting in FM coupling even two Zn atoms locate at close crystal lattice. Calculations show the two-X-doped AlNNSs have FM states with Curie temperatures (Tc) higher than 600 K, indicating that X-doped AlN systems are promising candidates for spintronic devices in the future.

Based on first-principles calculations plus Hubbard U, we have studied the electronic structure and magnetic properties of Mn-doped IIIA-nitride monolayers. The substitution of Mn for Al or Ga atom induces a total magnetic moment of 4.00 µB per dopant, independent of the choice of functional. The doped AlN system is half-metallic at GGA + U (

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.

Auxetic materials, which possess a negative Poisson's ratio (NPR), have been a hot topic in materials science research. Through atomistic simulations, we theoretically rediscover a few novel two-dimensional (2D) VA-nitride (VA-N) binary compounds with δ-phosphorene-like structures. The structures in the δ-phase (except for δ-PN) exhibit better stability in terms of energy, thermodynamics, and mechanics with respect to their counterparts in the α- and β-phases. The structures in the δ-phase show semiconducting behaviors with direct band gaps falling in the visible light region. Interestingly, most structures in the α- and δ-phases (except for δ-BiN) exhibit large in-plane NPRs and excellent mechanical properties. The maximum NPR occurs along the zigzag (x) direction for the δ-phases and along the diagonal direction for the α-phases. Particularly, for α- and δ-SbN, the NPRs are -0.628 and -0.296, respectively. δ-SbN can sustain tensile strains of up to 22% and 35% with maximum stresses of 12.1 and 9.8 GPa in the zigzag and armchair directions, respectively. In addition, the transverse response can reach up to 6.6% at a strain of ∼18% along the armchair (y) direction for δ-SbN, which is considerably higher than those of other 2D auxetic materials. Our results reveal that 2D VA-N binary compounds have potential applications in designing 2D electromechanical and optoelectronic devices.

Based on density functional theory, the electronic structures and magnetic properties have been studied in MoS2 monolayer via substitutional doping of nonmagnetic elements (IA, IIA, and IIIA elements). The magnetic moment of those doped systems origins form the interplay between the crystal-field of MoS2 matrix and localized Mo 4d states. On the whole, these doped MoS2 monolayers exhibit a half-metal→spin gapless (or narrow gap) semiconductor→ferromagnetic semiconductor transition as the dopants change from IA to IIIA groups. Electron and hole doping by a potential gate can realize a transition from ferromagnetic semiconductor to half metal. In important, the spin-polarization direction is switchable depending on the doped carrier’s type.

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.

We explore the electronic structures and magnetic properties in Cu-doped MX 2 (=MoS 2 , MoSe 2 , MoTe 2 , and WS 2 ) based on density functional theory. A Cu dopant leads to a net moment of 5.0 or 1.0 μ B in MX 2 , which mainly depend on the size of crystal-field splitting relative to that of the spin splitting. No magnetism is observed in Cu-doped MoTe 2 . The local distortion around the Cu atom reduces the total magnetic moment in two-Cu-doped MX 2 . The magnetic coupling between the nearest neighboring Cu atoms is ferromagnetic for all the cases, but they demonstrate various magnetic ground states with the increasing distance between Cu atoms: the Cu-doped MoS 2 and WS 2 exhibit anti-ferromagnetic and nonmagnetic ground state, respectively. A long-range ferromagnetic or ferrimagnetic coupling is attributed to double-exchange interaction in Cu-doped MoSe 2 . Half-metallic ferromagnetism with Curie temperature above room temperature in Cu-doped MoSe 2 provides a useful guidance to engineer the magnetic properties of MoSe 2 in experiments.

Based on density functional theory using ab initio calculations, the electronic structure and magnetic properties of the B-, C-, N-, O-, F-, Cl-, Br-, and I-doped MoS 2 monolayer are investigated. The B-, C-, and N-doped systems are p -type doping, while the halogen-doped systems are n -type doping. C-doping leads fairly deep and highly localized states in the gap of MoS 2 without spin-splitting. O-doping result in a narrower band-gap for MoS 2 . At the PBE level, results show that all the doped systems, expect for C-doping and O-doping, exhibit half-metallic behaviors with a total magnetic moment of ∼1.0 μ B . At the HSE level, the Br-doped case remains half-metallic, while the other doped cases revert to magnetic semiconductor. The magnetic moment mainly comes from the unpaired Mo-4 d orbitals and the p orbital of the dopant, as well as the S-3 p states. The formation of local magnetic moment depend on the local structure around the dopant, the localization of Mo-4 d , variable valency of Mo cation, and the partially filled anion- p orbitals of the dopant itself. The long-range half-metallic ferromagnetic order is attributed to the double-exchange interactions.

The electronic, structural, and magnetic properties of the perovskite Co-doped BiFeO 3 have been investigated using density functional theory within the generalized gradient approximation plus Hubbard U correction (GGA+ U ). We discuss the changes that occur in the structural parameters, electronic structure, and magnetic properties of the Co-doped BiFeO 3 under the consideration of the impact of the 3 d electrons. The results show that a substitutional Co for Fe in BiFeO 3 produces a magnetic moment of − 1.0 μ B and a half-metallic property emerges. The ferromagnetic (FM) coupling is more stable and still presents a half-metallic property when two Co atoms substitute for Fe atoms in BiFeO 3 .

Using first-principles calculations, we have studied the electronic structure and magnetic properties in a IIIA-nitride monolayer doped with Cu. The substitutional Cu impurity induces a global magnetic moment of 2.00 μB. All the doped systems are half metallic at the GGA level, but are magnetic semiconductors at the HSE06 level. As the atomic number of the IIIA elements increases, the increasing covalency leads to a tendency towards delocalization of the local magnetic moment. The ground state magnetism is determined by the competition between the ferromagnetic p–p/p–d hybridization interaction and the anti-ferromagnetic super-exchange interaction. By using external strain, the magnetic ground state can be deliberately tuned.

Titanium dioxide (TiO2) has promising applications in photocatalysis and energy-conversion devices due to its low cost, outstanding conductivity, and excellent electrochemical activity. However, its large band gap and insufficient-sized surface hinder its applications under visible-light radiation, so designing a highly efficient TiO2-based electrode structure is challenging. Herein, we constructed novel van der Waals (vdW) heterostructures using two-dimensional hexagonal TiO2 (H-TiO2) and 2D MoS2 (WS2) components. By density functional theory, we found that the 2D H-TiO2 has robust stability in energy and mechanics, as well as higher ductility than graphene and MoS2. The estimated indirect band gap ranged within 4.30–4.62 eV, resulting in hardly any visible-light absorbance. The vdW heterostructures of MoS2/TiO2 and WS2/TiO2 had the following characteristics: direct band gap, type-II band alignment, built-in electronic field, mobility as high as that of MoS2 (WS2), and remarkably improved visible-light absorption. These features enabled the heterostructures to have highly improved photocatalytic performance and solar-to-electric power conversion efficiency. Thus, these materials have high potential application in photocatalytic water splitting and solar energy-conversion devices.

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.

First-principles calculations have been used to investigate electronic and magnetic properties of zigzag graphene nanoribbon (ZGNR) with side-attached CH2 groups. The CH2 suppressed the magnetic states of pristine ZGNR within 12 A. As the relative amount of CH2 decreases, the ZGNR with CH2 pairs located at each edge experiences a transition from a nonmagnetic state to an anti-ferromagnetic one. The energy gap opens in the nonmagnetic state. When only systems with a CH2 attached at one edge, they exhibit ferromagnetic or ferrimagnetic states depend on number of CH2. The CH2 group saturates both σ and π bonds of ZGNR, and thus opens the band-gap of ZGNRs and enhances the stability of the ZGNRs. Therefore, the ZGNR provide a wide range of possible electronic and magnetic properties based on the same ribbon structure but different sites and numbers of CH2 groups.

Based on ab initio density functional theory calculations within the generalized gradient approximation, the electronic structure and magnetic properties of the one- and two-C-doped CdS monolayer are investigated. The results show that the C-doped CdS system exhibits half-metallic behaviors with a total magnetic moment of 2.0μB/C, which is in good accord with the results obtained from the HSE06 functional. The magnetic moment mainly comes from the spin-polarized C-2p states in the band gap. The long-range ferromagnetic order with a Curie temperature of about 280 K is attributed to the p–d and p–p hybridizations via the C–Cd–S coupling chains.

Using first-principles calculations, we have studied the structural, electronic, and magnetic properties in CdS monolayer doped with nonmagnetic (NM) atoms X (X = B, C, N, and O). The total magnetic moments are about 1.0, 2.0, 1.0, and 0.0 µB per supercell for the B-, C-, N-, and O-doped systems, respectively. As the electronegativity of X element increases, the local magnetic moment tends to localize and the impurity states gradually approach the valence band maximum of the host CdS. We find that the CdS monolayer with one S atom per supercell substituted by a B or C atom is half-metallic (HM), while that with an N atom per supercell is a ferromagnetic (FM) semiconductor. As for the one-oxygen doped case, the system still remains a semiconductor. Upon two S atoms per supercell substituted by X (=B, C, and N) atom, the X-doped CdS systems exhibit various magnetic ground states. As a consequence of the competition between double-exchange and super-exchange, the two-B-doped CdS system displays NM and anti-magnetic (AFM) behaviors, while the two-C-doped CdS system shows HM ferromagnetism with a Curie temperature of 280 K. However, the two-N-doped CdS system is a semiconductor with weakly AFM ground state. Our study demonstrates that the NM elements doping is an efficient route to tune the magnetic and electronic properties in CdS monolayers.

We employ spin-polarized density functional theory (DFT) calculations within generalized gradient approximation (GGA) to study the electronic structure and magnetic properties of C-doped SnO 2 (SnO 2 :C) bulk and thin films. Our results indicate that a singly substitutional C (C O ) does not induce magnetism, while the C O –C O pairs can unexpectedly activates short-range ferromagnetism in SnO 2 bulk. The intrinsic defect O vacancy (V O ) triggers local moment on the isolated C O atom but do not enhance the ferromagnetic (FM) coupling between C O atoms. When the substitutional C O atoms located at the surface of SnO 2 thin films, system exhibits anti-ferromagnetic (AFM) feature, which is inconsistent with experimental observation. This diversity of magnetic behavior in SnO 2 :C system highlights the delicate interplay between electron correlations and localization. The magnetic properties are closely related to the intrinsic defect V O and the reduction of some Sn +4 ions to Sn +2 as a possible charge compensation mechanism.

We report the structural, electronic, magnetic, and elastic properties of a two-dimensional (2D) honeycomb stannic oxide (SnO

Using first-principles calculations, we have studied the structural, electronic and magnetic properties of semi-fluorinated CdS sheets. The fluorination results various stable conformations with diversities of electronic and magnetic properties. The HCF–CdS conformation exhibits a half-metallic behavior with a net magnetic moment of 1.00 μ B per unit cell. The ferromagnetism with Curie temperature ( T C ) above room temperature (RT) is stabilized by the hole-medicated p–p exchange coupling between the S-3p states. The CdS–F conformation shows half-metallic characteristic and ferromagnetic semiconductor using GGA-PBE and HSE06 schemes, respectively. The CdS–FI conformation is a ferromagnetic semiconductor obtained by GGA-PBE calculation.

To tailor the bandwidth and the group-velocity dispersion, we demonstrate a novel waveguide based on a photonic crystal within a triangular array with crescent-like-shaped air holes. By changing the angle between the waveguide axis and symmetric axis of the air hole from 0 to π /2, we find that the available bandwidth with a nearly constant group index in excess of 22 increases from 7 nm to 13 nm, that the corresponding normalized delay-bandwidth product increases from 0.202 to 0.245, and that the absolute value of the group-velocity dispersion decreases from 13.500 ps 2 /km to 10 ps 2 /km. The origin of all the findings is related to the widening of the slow-light region with the increasing of the angle.

Based on first-principles spin-polarized density functional theory calculations, the relative stability, electronic structures, and magnetic properties of semi-fluorinated gallium nitride (GaN) sheets are investigated. The most stable conformation exhibits ferromagnetic (FM) ground state with a magnetic moment of about 1.0µB per fluorine. The half-metallic ferromagnetism is mainly attributed to the charge transfers from N to F atoms. Fluorination leads to unpaired spins in N-2pz states and unsaturated F-2p orbitals. The hole-mediated double exchange is responsible for the ferromagnetism in GaN sheets. In addition, GaN nanoribbons (GaNNRs) fluorinated only Ga edges are FM. This opens a route toward metal-free magnetic materials which have a huge possibility of making spintronic devices and nanomagnets.

Based on density functional theory calculations, we have studied the electronic structures and magnetic properties of passivated AlN nanowires (NWs) with Mg dopants. The calculated results show that double Mg atom doped passivated AlN NWs display ferromagnetic properties, and the total magnetic moment is 1.80 µB per 96-atom unit cell excluding the pseudohydrogen atoms. However, a couple of Mg atom doped bare AlN nanowire unit cells display anti-ferromagnetic (AFM) properties. Unequal properties of magnetic coupling in different Mg-doped AlN structures are due to the different localization and overlapping of impurity wave functions. It is also found that the ferromagnetic stability and Curie temperature of the passivated AlN NWs are much higher than those of bulk structures.

The electronic structures and magnetic properties of Ag-doped SnO2 have been investigated using first-principles spin-polarized calculations based on density functional theory. Our results demonstrate that Ag doping introduces spin polarization in SnO2 and gives rise to a local magnetic moment of 1.0 µB per substitutional silver ion. The hole-mediated ferromagnetic (FM) coupling between two Ag ions in this material is possibly ascribed to a p–d hopping interaction between O and Ag ions. The oxygen vacancy (VO) plays an important role in determining the magnetic properties of the Ag-doped SnO2 system. It is found that the VO does not induce magnetism in bulk SnO2. The VO enhances stability of the spin-polarized state for the case of the single-Ag-doped system, and imposes an intricate effect on a pair of Ag-doped configurations. For example, the FM coupling between two Ag ions is possibly reinforced if VO is sufficiently far away from them. The result indicates that Ag-doped SnO2 is a promising candidate for applications in future spintronic devices.

The electronic structures and magnetic properties for Rh-doped SnO2 crystals have been investigated by density functional theory. The results demonstrate a magnetic moment, which mainly arises from d orbital of Rhodium, of 1.0 μB per Rhodium with a little contribution from the Oxygen atoms surrounding it. The Rh-doped SnO2 system exhibits half-metallic ferromagnetism with high Curie temperature. Several doped configurations calculations show that there are some robust ferromagnetic couplings between these local magnetic moments. The p–d hybridization mechanism is responsible for the predicted ferromagnetism. These results suggest a recipe obtaining promising dilute magnetic semiconductor by doping nonmagnetic elements in SnO2 matrix.

Based on first-principles spin-polarized density functional theory (DFT) calculations, the geometric, electronic structures, and magnetic properties of semihydrogenated gallium nitride (GaN) sheet are investigated. The H-GaN conformation exhibits ferromagnetic (FM) ground state with a magnetic moment of about 1.0 μ B per unit cell. The ferromagnetism is mainly attributed to the decrease in the charge transfer from Ga to N atoms after hydrogenated, which leads to the partial occupancy of the N-2p z orbitals. The half-boat conformation is predicted to be the most stable structure with an indirect bandgap of 2.34eV. While the GaN-H conformation shows metallic behavior without magnetism.

The electronic structures and magnetic properties of N-doped CeO2 crystals have been investigated by first-principles calculations based on density functional theory with and without U. The results demonstrate a magnetic moment of 1.00μB per N obtained from all schemes. Predictions based on both LSDA and GGA calculations with and without U capture a half-metallic ground state for the N-doped CeO2 system. Several doped configurations calculations within LSDA demonstrate that there exist robust ferromagnetic couplings between these local magnetic moments, which mainly stem from Hund’s rule coupling. The hole-mediated long-range double exchange mechanism is responsible for the predicted ferromagnetism. It turns out that the percolation concentration needed to establish the collective ferromagnetism is at a few percent. However, further test calculations show that a weakly half-metallic ground state is predicted by GGA+U for this system.

Based on first-principles spin-polarized density functional theory calculations, the electronic and magnetic properties of nitrogen-doped monoclinic β -phase gallium oxide are investigated. Calculations predict that the spin-polarized state is stable with a magnetic moment of about 1.0 μB per nitrogen-dopant. The magnetic moment mainly arises from the p orbital of nitrogen, with a little contribution from the Oxygen atoms surrounding it. Magnetic coupling between different nitrogen atoms is discussed, and the results show that the hole-mediated short-range p–p exchange mechanism is responsible for the predicted ferromagnetism. Calculations also reveal that experimentally observed red-shift should be N-2p gap states to band transition.

Based on first-principles spin-polarized density functional theory calculations, the electronic structures and magnetic interactions of Ni-doped β -Ga 2 O 3 are investigated. Calculations predict that the spin-polarized state, with a magnetic moment of about 1.0 or 3.0 μ B per Ni-dopant when one Ni atom substitutes the octahedral or tetrahedral site, is more favorable in energy than that of non-spin polarized state. Ferromagnetic state, with an ordering temperature above room-temperature, is most stable for the structure in which one Ni substitutes the octahedral site.