The interfacial electronic structure of Fe3O4/BaTiO3 heterostructures was investigated using first-principles calculations. Owing to the two TiO-polarization directions, FeBO-terminated models show different interfacial binding strengths. Compared with the OTi–FeBO model, the TiO–FeBO model shows a spin polarization of 100% due to the hybridization effect of Ti 3d and FeB 3d at the Fermi level, which can be modulated by the electric field and TiO polarization directions. Negative electric field can control the strength of the hybridization of the interfacial Ti and O with FeB, but the positive electric field has no significant effect on it. The tunable high spin polarization at Fe3O4/BaTiO3 interfaces has potential applications in spintronic devices.

The semimetallic WTe2 has sparked intense interest owing to the non-saturating magnetoresistance, pressure-driven superconductivity and possession of type-II Weyl fermions. The unexpected and fascinating quantum properties are thought to be closely related to its delicate Fermi surface and a special electron–hole-pocket structure. However, in the single-layer limit, the electron–hole-pocket structure is missing owing to the lack of interlayer interaction. Herewith, we demonstrate that 3d transition-metal adsorption is an effective method to modify the electronic properties of monolayer WTe2 by density functional theory. Spin-splitting and spin-degenerate bands are realized in Ti-, V-, Cr-, Mn-, Fe-, and Co- and Sc-, Ni-, Cu-, and Zn-adsorbed systems, respectively. Especially, the reemergence of the electron–hole pockets appears in the Ni-adsorbed system. The calculated results are robust against inclusion of spin–orbit coupling and Coulomb interaction.

The use of molecular modification on magnetism has gained considerable interest in the development of multifunctional molecular spintronics. Such hybrid structures of nonmagnetic molecules and ferromagnetic metals manifest great promises of producing novel electric and magnetic features. The external electric field effect on the magnetism of C6H6-adsorbed Fe3O4(001) surface is elucidates by density functional theory calculations. The reduced magnetic moments of partial octahedral Fe atoms in the first layer break the spherical spatial spin density distribution. Such modification that is independent of the direction of electric field can be attributed to the charge redistribution as a result of screening effect, which changes orbital occupancy in unpaired octahedral Fe-d electrons near EF accompanied by a spin flip. Furthermore, octahedral Fe atom underneath C atom changes only as the applied field is large enough. Additionally, it is shown that the study of modulation on surface magnetism through external electric field is expected to excite a new area in molecular spintronics, such as the potential applications in electrically controlled magnetic data storage.

•Tunable half-metallicity and orbital rearrangement appear at strained Fe3O4/BaTiO3 interface.•The interfacial half-metallicity changes into insulator as strain releases.•The half-metallicity to insulator transition can be attributed to the interfacial interaction.Biaxial-strain effect emerges as one of leading topics for the strong influence on interfacial properties of nanoscale thin films. The tunable electronic characteristics in strained Fe3O4/BaTiO3 heterostructure have been investigated by first-principles calculation. Two models (OTi-FeBO and TiO-FeBO) are considered in the calculation, which is different in polarization directions of ferroelectric BaTiO3. Tunable half-metallicity (HM) and orbital rearrangement of interfacial layers are found in strained OTi-FeBO. The HM to insulator transition can be attributed to the orbital rearrangement of interfacial interaction. The interfacial properties are modulated by different biaxial-strains and the HM to insulator transition mechanism at different strain is proposed. The research is useful in ferroelectric memories application.Download high-res image (120KB)Download full-size image

The electronic structure of transition metal (TM) adsorbed two-dimensional g-C2N is investigated by first-principles calculations. Most of TM-adsorbed g-C2N show metallic properties, but Ni and Zn adsorptions show a band gap of 0.6 and 1.6 eV. The maximum spin splitting of TM-adsorbed g-C2N from Sc to Zn is 110, 186, 117, 100, 0, 515, 147, 64, 95 and 0 meV, respectively. The magnetic moments of adsorbed structure from Sc to Co are in the range from 0.15 to 2.11 μB, while in Ni, Cu and Zn adsorbed cases no magnetic moments appear. In Fe-adsorbed g-C2N, the adsorption structure at site of Fe12 generates a 90 meV band gap, where the adsorption sites at CC and CN rings are marked as Fe1 and Fe2. The maximum spin splitting is 515, 412 and 750 meV as Fe atomic concentration is 5.56%, 11.11% and 16.67%. Our results can bring more significant basis on the design of spintronic and valleytronic devices.

The electronic properties of monolayer WTe2 on top of Fe3O4(111) are investigated by density functional theory. We find that the substrate termination of Fe3O4(111) can switch the conductivity of monolayer WTe2 from the p- to n-type. However, the stacking pattern can critically influence its electronic structure. For Fe(A)-terminated interfaces, stronger-bonding models show Fermi level pinning. Additionally, the time-reversal symmetry is broken by the proximity that leads to valley polarization. With particular stacking patterns, large valley splittings of 139, −76 and −72 meV are obtained for Fe(A)-, Fe(B)- and O-terminated models, respectively. Moreover, Fe(B)- and O-terminated ones have more applicable significance for valleytronics as no interference of the interface state appears at the valence band maximum. We demonstrate that proximity to a room-temperature ferromagnet is a convenient way to obtain valley polarization and adjust the conductivity of monolayer WTe2.

The electronic structure of black phosphorene (BP)/monolayer 1H-XT2 (X = Mo, W; T = S, Se, Te) two dimensional (2D) van der Waals heterostructures have been calculated by the first-principles method. It is found that the electronic band structures of both BP and XT2 are preserved in the combined van der Waals heterostructures. The WSe2/BP van der Waals heterostructure demonstrates a type-I band alignment, but the MoS2/BP, MoSe2/BP, MoTe2/BP, WS2/BP and WTe2/BP van der Waals heterostructures demonstrate a type-II band alignment. In particular, the n-type XT2/p-type BP van der Waals heterostructures can be applied in p–n diode and logical devices. Strong spin splitting appears in all of the heterostructures when considering the spin orbital coupling. Our results play a significant role in the prediction of novel 2D van der Waals heterostructures that have potential applications in spin-filter devices, spin field effect transistors, optoelectronic devices, etc.

We study the geometric, electronic properties, and spin splitting in monovacancy (MV) and divacancy (DV) antimonene with five different models using first-principles calculations. Meanwhile the influence of spin–orbit coupling (SOC) is included. Different vacancies cause different geometric structures with or without inversion symmetry and influence the electronic structures. MV antimonene shows metallic character, however, four DV antimnoene models preserve the semiconducting character narrowing the band gap. The inversion asymmetry and SOC lead to the spin splitting in MV and two DV models. Zeeman-type spin splitting appears with out-of-plane spin polarization along M–K–Γ. Rashba and Dresselhaus effects induced spin splitting occurs at Γ and M points in MV.

The geometry, electronic structure and magnetic properties of the interfaces between Co (0001) and monolayer, bilayer, and trilayer antimonene with different stacking models were investigated. The Co d and Sb sp orbitals show a strong hybridization near EF, and strong chemical bonds form between Co and antimonene at the interface. Antimonene demonstrates a spin polarization of 12% at the 1T interface. After the contact, a high Schottky barrier is formed and the barrier height can be tuned by different Co/antimonene stacking patterns. With increasing the number of layers of antimonene, the barrier height decreases. These results have potential applications in spin diodes or spin field effect transistors based on antimonene.

•Current-in-plane electronic transport properties of Co40Fe40B20/SiO2/Si structures have been investigated firstly.•A two current channels model has been proposed to explain the metal-insulator transition of Co40Fe40B20/SiO2/Si structures.•Co40Fe40B20/SiO2/Si structures exhibit anomalous Hall effect.Co40Fe40B20/SiO2/Si structures fabricated by a facing-target sputtering method exhibit anomalous Hall effect. The longitudinal resistance shows a metal-insulator transition with the increase of temperature. The Hall resistance first increases, and then decreases with the increase of temperature. The character of Hall loops undergoes a crossover from AHE to ordinary Hall effect with the increase of temperature. Such electronic transport properties can be understood by a two current channels model. On the other hand, the critical saturated magnetic field of Hall loops drops rapidly at 350 K, which can be attributed to the reduction of spin-polarized carriers in Co40Fe40B20.Co40Fe40B20/SiO2/Si structures exhibit anomalous Hall effect.

•Magnetism appears in O-doped phosphorene, becoming a spin-gapless semiconductor.•B, F and C-doped system is n-type, p-type semiconductor and metal, respectively.•The magnetism of co-doped system depends on the sites and distance of two O atoms.We calculate the electronic structure and magnetism of monolayer phosphorene doped by nonmagnetic atoms. O, S and Se impurities can induce the magnetic moment. O doping makes it become a spin-gapless semiconductor, but S and Se doping induces a half-metallic characteristic. The p orbital of dopant has a strong hybridization with P around impurities, which induces spin splitting of P and impurities. C induces a metallic character. B acts as n-type dopant and F results in p-type dopant. The magnetism of phosphorene doped by two O atoms strongly depends on the doping sites and distance between two O atoms.Download high-res image (264KB)Download full-size image

We perform an ab initio simulation on the structural and electronic properties of van der Waals monolayer arsenene/FeCl2 heterostructures. Spin splitting appears at the conduction band minimum of arsenene due to interfacial coupling between As p and Cl p, Fe d states in the spin-down channel. The maximum splitting energy is 123 meV in all stacking configurations. Moreover, the splitting energy can be tuned by a perpendicular electric field. At a field of 5 V/nm, the spin-splitting direction can be inversed, and the splitting energy is −66 meV. Additionally, the positive electric field makes the system turn from an Ohmic contact into a Schottky one, which realizes a continuous modulation on the barrier height. More importantly, the electric control of spin-splitting inversion can be converted into an electric potential difference in arsenene according to the anomalous Hall effect. The transformation from spin-manipulation information to electric signal is useful in spintronic devices.

The fascinating spinterfaces between benzene and La2/3Sr1/3MnO3 (LSMO) are investigated based on the first-principles calculations. LSMO is a traditional high spin-polarized material used as the electrode in organic spintronic devices. However, the understanding of spin characteristics at organic/LSMO interfaces is unclear. Therefore, we study the benzene/LSMO spinterfaces to clarify the spin behaviors at organic/LSMO interfaces because benzene is the basic unit of organic molecules. It is found that SrO terminations have weak binding with benzene, showing the inert properties. More importantly, the positive spatial spin polarization expands into the benzene layer and vacuum layer in all of the models. To further make sure the credibility of the results, both the effect of the ordering of Sr atoms and the adsorption density of benzene are considered in our calculations. There is no spatial spin-polarization inversion above the benzene plane in all of the models. The results indicate that the organic layer can carry large spin polarization at organic/LSMO spinterfaces.

By first-principles calculations on tetragonal La2/3Sr1/3MnO3(LSMO)/BiFeO3(BFO) heterostructures, we demonstrate two interfacial couplings, direct and indirect, for achieving the net Fe moment in the first layer of interfacial regions. The direct Fe–-Mn (indirect Fe+-OB-MnO) exchange couplings induce a net Fe moment of 0.55 μB (−1.07 μB) in MnO2/Fe–O2 (MnO2/O2–Fe) model, which is parallel(antiparallel) to adjoining Mn around interfaces. Especially, the interfacial net Fe moment in MnO2/Fe–O2 model with 100% spin polarization can be reversed into the opposite direction by an electric field. In the spin-valve device, such controllable interfaces will develop a specific magnetic field region, where the external electric field can modulate the high and low magnetoresistances. These results lay foundations for developing energy-efficient spintronics and multifunctional devices.

Using first-principles calculations, we investigate the electronic and magnetic properties of orthoferrite LaTiO3/tetragonal BiFeO3 superlattices with different terminations. The interfacial electronic reconstruction along with formed chemical bonds transforms LaTiO3 into a metal by means of the Anderson and Mott transition. In particular, a two-dimensional electron gas appears at interfacial regions located in LaTiO3 of model LaO–BiO and BiFeO3 of model TiO2–BiO due to the d–p, d–d electron interactions and ferroelectric polarization. Moreover, the Fe and Ti magnetic moments are sensitive to the interfacial geometry and hybridization, and a 19% spin polarization of LaTiO3 is gained in model TiO2–FeO2. Our results demonstrate that the interfacial geometry and hybridization can successfully tune the Fermi energy and the Hubbard band of LaTiO3, and novel physical properties in different models provide opportunities for developing functional nanoelectronic devices.

The superlattice of energetically stable La2/3Sr1/3MnO3 and tetragonal BiFeO3 is investigated by means of density functional theory. The superlattice as a whole exhibits a half-metallic character, as is desired for spintronic devices. The interfacial electronic states and exchange coupling are analyzed in details. We demonstrate that the interfacial O atoms play a key role in controlling the coupling. The higher ferroelectricity of tetragonal BiFeO3 and stronger response to the magnetic moments in the La2/3Sr1/3MnO3/BiFeO3 superlattice show a strongly enhanced electric control of the magnetism as compared to the rhombohedral one. Therefore, it is particularly practical interest in the magnetoelectrically controlled spintronic devices.Keywords: electronic structure; interfacial coupling; magnetic properties; multiferroic; spintronics;

Anisotropic magnetoresistance (AMR) of the facing-target reactively sputtered epitaxial γ′-Fe4N/CoN bilayers is investigated. The phase shift and rectangular-like AMR appears at low temperatures, which can be ascribed to the interfacial exchange coupling. The phase shift comes from the exchange bias (EB) that makes the magnetization lag behind a small field. When the γ′-Fe4N thickness increases, the rectangular-like AMR appears. The rectangular-like AMR should be from the combined contributions including the EB-induced unidirectional anisotropy, intrinsic AMR of γ′-Fe4N layer and interfacial spin scattering.Keywords: anisotropic magnetoresistance; bilayer; exchange bias; facing-target sputtering; Fe4N

The anomalous Hall effect (AHE) in the reactively sputtered epitaxial and polycrystalline γ′-Fe4N films is investigated systematically. The Hall resistivity is positive over the entire temperature range. The magnetization, carrier density and grain boundary scattering have a major impact on the AHE scaling law. The scaling exponent γ in the conventional scaling of ρAH ∝ ργxx is larger than 2 in both the epitaxial and polycrystalline γ′-Fe4N films. Although γ > 2 has been found in heterogeneous systems due to the effects of the surface and interface scattering on AHE, γ > 2 is not expected in homogenous epitaxial systems. We demonstrated that γ > 2 results from residual resistivity (ρxx0) in γ′-Fe4N films. Furthermore, the side-jump and intrinsic mechanisms are dominant in both epitaxial and polycrystalline samples according to the proper scaling relation.

The electronic structure and magnetic properties of the tetragonal La2/3Sr1/3MnO3/BiFeO3 multiferroic superlattices with different interfacial terminations have been studied by first-principles calculations. Our results for all the models of the tetragonal La2/3Sr1/3MnO3/BiFeO3 superlattices exhibit a metallic electronic structure. More importantly, we find that the magnetoelectric coupling can be realized in the tetragonal La2/3Sr1/3MnO3/BiFeO3 heterostructures by means of exchange bias, which can be attributed to the interfacial exchange coupling. These findings are useful for magnetoelectrically controlled spintronic devices.

•Strong Fe–Si ionic bond is formed in the Fe4N/Si bilayers.•Spin polarization is induced in Si and the Fe4N magnetic moments are reduced.•The interfacial bonding is weak in the Fe4N/graphene bilayers.•The charge transfer from graphene to Fe4N is from the difference of work functions.We perform the first-principles simulation on the interfacial electronic structures and magnetic properties of Fe4N(0 0 1)/Si and Fe4N(1 1 1)/graphene bilayers. For Fe4N/Si bilayers, the strong interfacial bonding reduces the Fe4N magnetic moment, but induces the spin polarization in Si with a magnetic moment of −0.06 μВ for Si located at the bottom of interfacial FeI atom. For Fe4N/graphene bilayers, the interfacial bonding is so weak that the reduced Fe4N magnetic moment only comes from the compressive strain modulation due to the large lattice mismatch. The observed p-type doping of graphene is induced by a larger work function of Fe4N(1 1 1) surface than that of graphene. Our results demonstrate that the interfacial bonding between Fe4N and Si/graphene plays a significant role in manipulating their electronic properties.Graphical abstract

•For ultrathin films, two different scaling at different temperature regions appear.•Thicker films show a metallic character with only one scaling relation.•In dirty regime, an unconventional scaling relation is σAH∝σxxα with α=1.99.Scaling of anomalous Hall effect in amorphous CoFeB films with thickness ranging from 2 to 160 nm has been investigated. We have found that the scaling relationship between longitudinal (ρxx) and anomalous Hall (ρAH) resistivity is distinctly different in the Bloch and localization regions. For ultrathin CoFeB films, the sheet resistance (Rxx) and anomalous Hall conductance (GAH) received quantum correction from electron localization showing two different scaling relationships at different temperature regions. In contrast, the thicker films show a metallic conductance, which have only one scaling relationship in the entire temperature range. Furthermore, in the dirty regime of localization regions, an unconventional scaling relationship σAH∝σxxα with α=1.99 is found, rather than α=1.60 predicted by the unified theory.

The spin-polarization related properties of interface between benzene and Fe4N is calculated by first-principle theory. The subtleties due to the atomic layers of Fe4N are focal points in this work. First, the Fe4N surface is distorted significantly due to benzene adsorption. Fe atoms beneath benzene move toward the center, under the strain’s competition between benzene and the bottom atomic layer, when Fe4N has five and seven atomic layers. Second, the spin-polarization inversion due to the p–d Zener exchange interaction appears in a wide zone. Third, antiferromagnetic alignment is discovered at the first atomic layer of Fe4N surface with five and seven atomic layers, and it is rare that magnetic properties of the substrate can be influenced so significantly. This discovery suggests that the switch between the ferromagnetic and antiferromagnetic alignment in the atomic-scale zone, especially when the Fe4N is the electrode, should be considered in the analysis on magnetic properties of organic tunneling junction or organic spin valve.

•Fe4N/Alq3/Co organic spin valves exhibit an inverse magnetoresistance.•Asymmetric magnetoresistance is attributed to interfacial magnetic coupling.•The advantages of facing-target sputtering make interfacial diffusion weak.Spin-dependent electronic transport and magnetic properties of Fe4N/tris(8-hydroxyquinoline) aluminum (Alq3)/Co organic spin valves (OSVs) are investigated. Fe4N/Alq3/Co OSVs with different Alq3 thicknesses t exhibit an inverse magnetoresistance (MR), which comes from the opposite effective spin polarization at the two ferromagnetic electrode/Alq3 interfaces. For the antiparallel configurations, MR at 3 K presents the obvious asymmetry, corresponding to the asymmetric hysteresis loop. The asymmetric loops of magnetization and MR can be attributed to the magnetic coupling at the Alq3/Co interface. The interfacial diffusion between Co and Alq3 is weak due to the advantages of facing-target sputtering. Below 120 nm, MR increases with the increased t owing to the decreased effect of the ill-defined layer. The reduced MR at 260 nm is ascribed to the decline of spin polarization.

Magnetic and electronic properties of Fe4N(111)/MoS2(√3 × √3) superlattices are investigated by first-principles calculations, considering two models: (I) FeIFeII–S and (II) N–S interfaces, each with six stacking configurations. In model I, strong interfacial hybridization between FeI/FeII and S results in magnetism of monolayer MoS2, with a magnetic moment of 0.33 μB for Mo located on top of FeI. For model II, no magnetism is induced due to weak N–S interfacial bonding, and the semiconducting nature of monolayer MoS2 is preserved. Charge transfer between MoS2 and N results in p-type MoS2 with Schottky barrier heights of 0.5–0.6 eV. Our results demonstrate that the interfacial geometry and hybridization can be used to tune the magnetism and doping in Fe4N(111)/MoS2(√3 × √3) superlattices.Keywords: electronic structure; Fe4N; magnetic properties; MoS2;

An enhanced anomalous Hall effect is observed in heterogeneous uniform Fe cluster assembled films with different film thicknesses (ta = 160–1200 nm) fabricated by a plasma-gas-condensation method. The anomalous Hall coefficient (Rs) at ta = 1200 nm reaches its maximum of 2.4 × 10−8 Ω cm G−1 at 300 K, which is almost four orders of magnitude larger than bulk Fe. The saturated Hall resistivity (ρAxy) first increases and then decreases with the increase of temperature accompanied by a sign change from positive to negative. Analysis of the results revealed that ρAxy decreases with increasing longitudinal resistivity (ρxx) on a double-logarithmic scale and obeys a new scaling relation of log(ρAxy/ρxx) = a0 + b0 logρxx.

The geometry, bonding, electronic and magnetic properties of Fe4N/oxides (MgO, BaTiO3 and BiFeO3) interfaces with different configurations are performed using first-principles calculations. The n- and p-type doping of MgO are induced in FeIFeII/MgO and (FeII)2N/MgO interfaces, respectively. The metallic characteristics are induced in BaTiO3 by contact with FeIFeII termination, followed by p-type doping in the (FeII)2N/BaO interface and n-type doping in the (FeII)2N/TiO2 interface. The interfacial dipole due to charge rearrangement may induce the Fermi level pinning in the Fe4N/MgO and (FeII)2N/BaTiO3 systems. The deposition of Fe4N on BiFeO3 leads to a metallic character of BiFeO3 with total magnetic moments of 0.33–1.54 μB. The different electronic and magnetic characters are governed by interfacial bonding between Fe4N and oxides. These findings are useful for the future design of Fe4N/oxides based spintronics devices.

Magnetic and electronic properties of Cu1−xFexO systems with x = 6.25% and 12.5% have been investigated using first principles calculations. The ground state of CuO is an antiferromagnetic insulator. At x = 6.25%, Cu1−xFexO systems with Fe on 2 and 4 substitution positions are half-metallic due to the strong hybridization among Fe, the nearest O and Cu atoms, which may come from the double exchange coupling between Fe2+–O2−–Cu2+. At x = 12.5%, Cu1−xFexO system with Fe on 9–11 position has a strong spin polarization near the Fermi level and the system energy is lowest when the doped two Fe atoms form ferromagnetic configuration. This indicates the two doped Fe atoms prefer to form ferromagnetic configuration in Fe2+–O2−–Cu2+–O2−–Fe2+ chains. While in the Fe on 7–11 position, the spin-down Fe–11 3d states have a large spin polarization near the Fermi level when the two doped Fe atoms form antiferromagnetic configuration. It is concluded that the transition metal doping can modify the magnetism and electronic structures of Cu1−xFexO systems.

•The reactive-sputtered polycrystalline Ti1 − xCrxN films are ferromagnetic.•The highest Curie temperature TC of ~ 120 K appears at x = 0.47.•The negative magnetoresistance is dominated by the double-exchange interaction.•The scaling ρxyA/n ∝ ρxx2.19 was observed.The reactive-sputtered polycrystalline Ti1 − xCrxN films with 0.17 ≤ x ≤ 0.51 are ferromagnetic and at x = 0.47 the Curie temperature TC shows a maximum of ~ 120 K. The films are metallic at 0 ≤ x ≤ 0.47, while the films with x = 0.51 and 0.78 are semiconducting-like. The upturn of resistivity below 70 K observed in the films with 0.10 ≤ x ≤ 0.47 is from the effects of the electron–electron interaction and weak localization. The negative magnetoresistance (MR) of the films with 0.10 ≤ x ≤ 0.51 is dominated by the double-exchange interaction, while at x = 0.78, MR is related to the localized magnetic moment scattering at the grain boundaries. The scaling ρxyA/n ∝ ρxx2.19 suggests that the anomalous Hall effect in the polycrystalline Ti1 − xCrxN films is scattering-independent.

Electronic structure and optical properties of α-FeMO3 systems (M = Sc, Ti, V, Cr, Cu, Cd or In) have been investigated using first principles calculations. All of the FeMO3 systems have a large net magnetic moment. The ground state of pure α-Fe2O3 is an antiferromagnetic insulator. For M = Cu or Cd, the systems are half-metallic. Strong absorption in the visible region can be observed in the Cu and Cd-doped systems. Systems with M = Sc, Ti, V, Cr or In are not half-metallic and are insulators. The strongest peaks shift toward shorter wavelengths in the absorption spectra. It is concluded that transition metal doping can modify the electronic structure and optical properties of α-FeMO3 systems.

The single-phase γ′-Fe4N films were fabricated using reactive sputtering. The x-ray diffraction peaks from γ′-Fe4N(111), (200) and (311) indicate that the films are γ′-Fe4N. The grain size increases with the increase of film thickness (t), and the grains grow with a columnar structure. All of the films are soft ferromagnetic at room temperature. The saturation magnetization decreases with the increasing temperature, and satisfies the modified Bloch's spin wave theory. The electrical transport properties show a metallic conductance mechanism, and the room-temperature resistivity decreases with the increasing t, revealing that the electron scattering increases with the decrease of t. The magnetoresistance (MR) evolves from positive to negative with the increase of temperature, and the transition temperature decreases with the increase of t. The positive MR at 5 K increases with the increasing t. The complex MR should be dominated by Lorentz force effect, the suppression of the electron scattering, and the shift of minority and majority spin bands under a magnetic field.Highlights► The single-phase γ′-Fe4N films were fabricated using reactive sputtering. ► The size of columnar grain increases with film thickness. ► The saturation magnetization satisfies the modified Bloch's spin wave theory. ► The films show a metallic conductance mechanism and a complex magnetoresistance.

Fe100−xPtx films with different Pt atomic fractions (x) and film thicknesses (tf) were fabricated by magnetron sputtering at room temperature and subsequently annealed at 650 °C. Their structure and magnetic properties have been investigated systematically. All the as-deposited Fe100−xPtx films with disordered face-centered-cubic (fcc) structure are soft ferromagnetic. The annealed Fe100−xPtx films evolve from Fe3Pt, FePt to FePt3 with increasing x. High-temperature annealing makes the Fe100−xPtx films transform from the disordered fcc structure to the ordered face-centered-tetragonal (fct) L10 structure as x is in the range of 40–60. The grain size of the annealed Fe52Pt48 films increases with increasing tf. All the annealed Fe100−xPtx films are hard ferromagnetic. The coercivity of the annealed Fe100−xPtx films first increases, and decreases latterly with increasing x. Meanwhile, the coercivity of the annealed Fe52Pt48 films decreases with increasing temperature.

The surface morphology of the (Fe1 − xCrx)0.09Cu0.91 films does not change significantly as x increases. No Fe or Cr granules form in the films because of the low deposition temperature and the non-equilibrium deposition procedure, suggesting that Fe and Cr atoms disperse in the Cu matrix. With increasing x, the lattice constant c and single cell volume decrease, but the lattice constants (a, b) first increase and latterly decrease. The films show spin-glass-like manner that looks like superparamagnetism at high temperatures and are ferromagnetic at low temperatures. The peak temperature of the zero-field-cooling curves decreases from 37 to 23 K as x increases from 0 to 0.25. Below the peak temperatures, the field-cooled magnetization decreases with decreasing temperature due to the antiferromagnetically coupling of the disordered spin-glass-like moments. The coercivity increases greatly below 50 K because of the pinning effect of the frozen spin-glass-like moments at low temperatures.

Structure, magnetic and electrical transport properties of the polycrystalline (Fe3O4)100 − xPtx composite films fabricated using DC reactive magnetron sputtering at ambient temperature were investigated systematically. It is found that the films are composed of inverse-spinel-structured polycrystalline Fe3O4 and Pt. Pt addition proves the growth of Fe3O4 grains with the (111) orientation. All the films are ferromagnetic at room temperature. The dominant magnetic reversal mechanism turns from domain wall motion to Stoner–Wohlfarth rotation with the increasing x. The electrical transport mechanism also changes with the increasing x because Pt addition decreases the height of the tunneling barrier at the Fe3O4 grain boundaries, and makes the magnetoresistance of the films decrease.

The electric field effects on the electronic structure of g-C2N/XSe2 (X = Mo, W) heterostructures are investigated by first-principles calculations. The g-C2N/MoSe2 heterostructure is an indirect semiconductor at an electric field from −0.1 to 0.3 V/Å. The band gap is 0.66, 0.54, 0.45, 0.39 and 0.34 eV, which almost changes linearly with the electric field. The maximum spin splitting at K point is 188 meV. The g-C2N/WSe2 heterostructure is still an indirect semiconductor at an electric field of −0.1 and 0 V/Å. At an electric field from 0.1 to 0.3 V/Å, the heterostructure with the valence band at Fermi level is a p-type semiconductor, where the band gap is 0.32, 0.26, 0.19, 0.12 and 0.06 eV and the maximum spin splitting at K point is 444 meV. Moreover, near Fermi level, the conduction band mainly comes from monolayer g-C2N, but the valence band comes from XSe2. Our results can bring much significant information on the potential applications in spintronic and field effect devices.

•For ultrathin films, two different scaling at different temperature regions appear.•Thicker films show a metallic character with only one scaling relation.•In dirty regime, an unconventional scaling relation is σAH∝σxxα with α=1.99.Scaling of anomalous Hall effect in amorphous CoFeB films with thickness ranging from 2 to 160 nm has been investigated. We have found that the scaling relationship between longitudinal (ρxx) and anomalous Hall (ρAH) resistivity is distinctly different in the Bloch and localization regions. For ultrathin CoFeB films, the sheet resistance (Rxx) and anomalous Hall conductance (GAH) received quantum correction from electron localization showing two different scaling relationships at different temperature regions. In contrast, the thicker films show a metallic conductance, which have only one scaling relationship in the entire temperature range. Furthermore, in the dirty regime of localization regions, an unconventional scaling relationship σAH∝σxxα with α=1.99 is found, rather than α=1.60 predicted by the unified theory.

The interfacial electronic structure of Fe3O4/BaTiO3 heterostructures was investigated using first-principles calculations. Owing to the two TiO-polarization directions, FeBO-terminated models show different interfacial binding strengths. Compared with the OTi–FeBO model, the TiO–FeBO model shows a spin polarization of 100% due to the hybridization effect of Ti 3d and FeB 3d at the Fermi level, which can be modulated by the electric field and TiO polarization directions. Negative electric field can control the strength of the hybridization of the interfacial Ti and O with FeB, but the positive electric field has no significant effect on it. The tunable high spin polarization at Fe3O4/BaTiO3 interfaces has potential applications in spintronic devices.

An enhanced anomalous Hall effect is observed in heterogeneous uniform Fe cluster assembled films with different film thicknesses (ta = 160–1200 nm) fabricated by a plasma-gas-condensation method. The anomalous Hall coefficient (Rs) at ta = 1200 nm reaches its maximum of 2.4 × 10−8 Ω cm G−1 at 300 K, which is almost four orders of magnitude larger than bulk Fe. The saturated Hall resistivity (ρAxy) first increases and then decreases with the increase of temperature accompanied by a sign change from positive to negative. Analysis of the results revealed that ρAxy decreases with increasing longitudinal resistivity (ρxx) on a double-logarithmic scale and obeys a new scaling relation of log(ρAxy/ρxx) = a0 + b0 logρxx.

The anomalous Hall effect (AHE) in the reactively sputtered epitaxial and polycrystalline γ′-Fe4N films is investigated systematically. The Hall resistivity is positive over the entire temperature range. The magnetization, carrier density and grain boundary scattering have a major impact on the AHE scaling law. The scaling exponent γ in the conventional scaling of ρAH ∝ ργxx is larger than 2 in both the epitaxial and polycrystalline γ′-Fe4N films. Although γ > 2 has been found in heterogeneous systems due to the effects of the surface and interface scattering on AHE, γ > 2 is not expected in homogenous epitaxial systems. We demonstrated that γ > 2 results from residual resistivity (ρxx0) in γ′-Fe4N films. Furthermore, the side-jump and intrinsic mechanisms are dominant in both epitaxial and polycrystalline samples according to the proper scaling relation.

The electronic structure and magnetic properties of the tetragonal La2/3Sr1/3MnO3/BiFeO3 multiferroic superlattices with different interfacial terminations have been studied by first-principles calculations. Our results for all the models of the tetragonal La2/3Sr1/3MnO3/BiFeO3 superlattices exhibit a metallic electronic structure. More importantly, we find that the magnetoelectric coupling can be realized in the tetragonal La2/3Sr1/3MnO3/BiFeO3 heterostructures by means of exchange bias, which can be attributed to the interfacial exchange coupling. These findings are useful for magnetoelectrically controlled spintronic devices.

The electronic properties of monolayer WTe2 on top of Fe3O4(111) are investigated by density functional theory. We find that the substrate termination of Fe3O4(111) can switch the conductivity of monolayer WTe2 from the p- to n-type. However, the stacking pattern can critically influence its electronic structure. For Fe(A)-terminated interfaces, stronger-bonding models show Fermi level pinning. Additionally, the time-reversal symmetry is broken by the proximity that leads to valley polarization. With particular stacking patterns, large valley splittings of 139, −76 and −72 meV are obtained for Fe(A)-, Fe(B)- and O-terminated models, respectively. Moreover, Fe(B)- and O-terminated ones have more applicable significance for valleytronics as no interference of the interface state appears at the valence band maximum. We demonstrate that proximity to a room-temperature ferromagnet is a convenient way to obtain valley polarization and adjust the conductivity of monolayer WTe2.

The electronic structure of black phosphorene (BP)/monolayer 1H-XT2 (X = Mo, W; T = S, Se, Te) two dimensional (2D) van der Waals heterostructures have been calculated by the first-principles method. It is found that the electronic band structures of both BP and XT2 are preserved in the combined van der Waals heterostructures. The WSe2/BP van der Waals heterostructure demonstrates a type-I band alignment, but the MoS2/BP, MoSe2/BP, MoTe2/BP, WS2/BP and WTe2/BP van der Waals heterostructures demonstrate a type-II band alignment. In particular, the n-type XT2/p-type BP van der Waals heterostructures can be applied in p–n diode and logical devices. Strong spin splitting appears in all of the heterostructures when considering the spin orbital coupling. Our results play a significant role in the prediction of novel 2D van der Waals heterostructures that have potential applications in spin-filter devices, spin field effect transistors, optoelectronic devices, etc.

Using first-principles calculations, we investigate the electronic and magnetic properties of orthoferrite LaTiO3/tetragonal BiFeO3 superlattices with different terminations. The interfacial electronic reconstruction along with formed chemical bonds transforms LaTiO3 into a metal by means of the Anderson and Mott transition. In particular, a two-dimensional electron gas appears at interfacial regions located in LaTiO3 of model LaO–BiO and BiFeO3 of model TiO2–BiO due to the d–p, d–d electron interactions and ferroelectric polarization. Moreover, the Fe and Ti magnetic moments are sensitive to the interfacial geometry and hybridization, and a 19% spin polarization of LaTiO3 is gained in model TiO2–FeO2. Our results demonstrate that the interfacial geometry and hybridization can successfully tune the Fermi energy and the Hubbard band of LaTiO3, and novel physical properties in different models provide opportunities for developing functional nanoelectronic devices.

The semimetallic WTe2 has sparked intense interest owing to the non-saturating magnetoresistance, pressure-driven superconductivity and possession of type-II Weyl fermions. The unexpected and fascinating quantum properties are thought to be closely related to its delicate Fermi surface and a special electron–hole-pocket structure. However, in the single-layer limit, the electron–hole-pocket structure is missing owing to the lack of interlayer interaction. Herewith, we demonstrate that 3d transition-metal adsorption is an effective method to modify the electronic properties of monolayer WTe2 by density functional theory. Spin-splitting and spin-degenerate bands are realized in Ti-, V-, Cr-, Mn-, Fe-, and Co- and Sc-, Ni-, Cu-, and Zn-adsorbed systems, respectively. Especially, the reemergence of the electron–hole pockets appears in the Ni-adsorbed system. The calculated results are robust against inclusion of spin–orbit coupling and Coulomb interaction.