Spin-dependent Density Of States Research Articles

Modeling and Simulation of High-Performance CrTe Intrinsic Half Metal-Based Spin Valve and Spin Diode

Most of the pristine two-dimensional materials such as graphene, silicene, germanene etc. are non-magnetic in nature and the creation of magnetism in these materials is subjected to the doping, external field, vacancy, strain etc., but their control in the experimental is very difficult. That has motivated the researchers for the exploration of 2D materials like Transition metal chalcogenides (TMC) with intrinsic magnetism. In the present study, the ferromagnetism of the two-dimensional Chromium telluride (CrTe) is verified by the spin-dependent density of states. Moreover, taking into consideration the similar crystal structure and comparable lattice constants of Vanadium telluride (VTe) to that of CrTe, we have modelled a three-layer spin valve (CrTe-VTe-CrTe) and a two-layer spin diode (CrTe-VTe), and simulated for spin-dependent transport characteristics. The performance parameters like spin injection efficiency, magnetoresistance, rectification ratio has been calculated to carry out the performance evaluation of the modelled devices. The spin valve displays 100% spin injection efficiency and large magnetoresistance of 3.46 × 108%, a comparative study has been carried out to evaluate the performance of the modelled spin valve. Moreover, the spin diode displays high spin filtering efficiency and good rectification ratio, which suggests the potential spintronic applications of the proposed devices. The spin-dependent transport characteristics have been justified by using spin-dependent transmission spectrum and spin-dependent band structure.

Theoretical Investigation in Coherent Manipulation throughout the Calculation of the Local Density of States in FM-DQD-FM Device

In this work, theoretical investigation in coherent manipulation throughout local density of states calculation for serially coupled double quantum dots embedded between ferromagnetic leads (FM-QD1-QD2-FM) by using the non-equilibrium Green's function approach. Since the local density of states are formulated incorporating the spin polarization and the type of spin configuration on the leads. Our model incorporates the inter-dot hopping, the intra-dot Coulomb correlation, the spin exchange energy and the coupling interactions between the quantum dots and leads. The results concerned to the parallel configuration at strong inter-dot coupling regime shows that the spin down electrons in the quantum dots may be more coupled coherently if the regime is tuned. The local density of states of the two dots for spin up electrons shows a broad hump with small splitting i.e. the case is decoherent for spin up electrons. In the case of weak interdot coupling it is obvious that the spin dependent density of states on the quantum dots show that the resonances are not well splitted. For the antiparallel configuration in the strong coupling regime, the spin dependent density of states of the double quantum dots show four peaks but with broaden and overlapping. In the case of weak coupling regime, the total spin dependent density of states, which have two peaks with certain board, one can conclude that the states are not coupled coherently. The case of the antiferromagnetic nature of the spin exchange interaction, our calculations for the parallel and antiparallel configurations (in strong and weak regimes) show a decoherence state.

Enhanced Photodegradation in Metal Oxide Nanowires with Co-Doped Surfaces under a Low Magnetic Field.

This work demonstrated the enhanced photodegradation (PD) resulting from Co-rich doping of ZnO nanowire (NW) surfaces (Co2+/ZnO NWs) prepared by combining Co sputtering on ZnO NWs and immersion in deionized water to exploit the hydrophilic-hydrophobic transitions on the ZnO surfaces resulting from Co atom diffusion. Because of the controllable spin-dependent density of states (DOS) induced by Co2+, the PD of methylene blue dye can be enhanced by approximately 90% (when compared with bare ZnO NWs) by using a conventional permanent magnet with a relatively low magnetic field strength of approximately 0.15 T. The reliability of spin polarization-modulation attained through surface doping, based on the magnetic response observed from X-ray absorption measurements and magnetic circular dichroism, provides an opportunity to create highly efficient catalysts by engineering surfaces and tailoring their spin-dependent DOS.

Spin filtering by proximity effects at hybridized interfaces in spin-valves with 2D graphene barriers

We report on spin transport in state-of-the-art epitaxial monolayer graphene based 2D-magnetic tunnel junctions (2D-MTJs). In our measurements, supported by ab-initio calculations, the strength of interaction between ferromagnetic electrodes and graphene monolayers is shown to fundamentally control the resulting spin signal. In particular, by switching the graphene/ferromagnet interaction, spin transport reveals magneto-resistance signal MR > 80% in junctions with low resistance × area products. Descriptions based only on a simple K-point filtering picture (i.e. MR increase with the number of layers) are not sufficient to predict the behavior of our devices. We emphasize that hybridization effects need to be taken into account to fully grasp the spin properties (such as spin dependent density of states) when 2D materials are used as ultimately thin interfaces. While this is only a first demonstration, we thus introduce the fruitful potential of spin manipulation by proximity effect at the hybridized 2D material / ferromagnet interface for 2D-MTJs.

Mass-imbalanced Hubbard model in optical lattice with site-dependent interactions

We study the half-filled mass-imbalanced Hubbard model with spatially alternating interactions on an optical bipartite lattice by means of the dynamical mean-field theory. The Mott transition is investigated via the spin-dependent density of states and double occupancies. The phase diagrams for the homogeneous phases at zero temperature are constructed numerically. The boundary between metallic and insulating phases at zero temperature is analytically derived within the dynamical mean field theory using the equation of motion approach as the impurity solver. We found that the metallic region is reduced with increasing interaction anisotropy or mass imbalance. Our results are closely relevant to current researches in ultracold fermion experiments and can be verified through experimental observations.

Magnetism, electronic structure and half-metallic property of transition metal (V, Cr, Mn, Fe, Co) substituted Zn3P2 dilute magnetic semiconductors: An ab-initio study

Abstract The ab-initio electronic structure calculations are used to investigate the half-metallic property, structural stability, spin dependent density of states and magnetism of transition metal (V, Cr, Mn, Fe, Co) substituted Zn 3 P 2 . Our results show the half-metallic ground state and ferromagnetic (antiferromagnetic) stability for small concentrations (2.5% and 5%) of transition metal atom substitution considered in our study. The structural and magnetic stability of the substituted compounds have been investigated through the calculation of the heat of formation and analyzing the minimum total energies corresponding to the ferromagnetic, antiferromagnetic and nonmagnetic phases. The substituted transition metal atom is found to give rise to magnetism of these compounds and half-metallic property is observed in many cases. We have used the spin, orbital and atom projected density of states to investigate this point and studied the nature of bonding in these systems using the charge density contours. We have observed from our calculations, magnetically stable phases and large values of the magnetic moments in these compounds and it suggests that these compounds may be useful materials for semiconductor spintronic devices. We have further calculated the theoretical X-ray diffraction pattern of these compounds.

Observation of tunnel magnetoresistance in a superconducting junction with Zeeman-split energy bands

The change of the quasiparticle density of states in a superconductor due to the Zeeman splitting can lead to highly responsive spintronic devices. This is demonstrated here in the magnetotunneling studies of a supercondcutor/insulator/ferromagnet tunnel junction. A tunnel magnetoresistance (TMR) as large as 36% is obtained, resulting from the conductance variation due to spin-split quasiparticle tunneling, and only occurs in the superconducting state. Our results show that in addition to the naturally existent spin imbalance in ferromagnets (upon which conventional TMR is obtained), we can manipulate tunnel conductance by tailoring spin dependent density of states with interfacial exchange fields, and even with a tunnel junction with both superconducting electrodes.

The electronic and optical properties of indium doped zinc oxide nanosheets

Electronic and optical properties of the pure ZnO crystal and In doped ZnO nanosheets (ZnONS) are systematically explored by using an accurate density functional method. The half-metallic properties are induced by the doping of Indium in ZnO nanosheets from the spin dependent density of states and band structure analysis. The optical properties of the In doped ZnONS, such as the absorption, refraction and reflectivity, show a red-shift corresponding to the dielectric function compared to that of the pure ZnONS. The new transition peaks near the Fermi levels are observed due to the In doping, which were deduced from the direct transitions of electrons from the impurity indium atom.

Graphene single-electron transistor as a spin sensor for magnetic adsorbates

We study single electron transport through a graphene quantum dot with magnetic adsorbates. We focus on the relation between the spin order of the adsorbates and the linear conductance of the device. The electronic structure of the graphene dot with magnetic adsorbates is modeled through numerical diagonalization of a tight-binding model with an exchange potential. We consider several mechanisms by which the adsorbate magnetic state can influence transport in a single electron transistor: by tuning the addition energy, by changing the tunneling rate and, in the case of spin polarized electrodes, through magnetoresistive effects. Whereas the first mechanism is always present, the others require that the electrode has either an energy or spin dependent density of states. We find that graphene dots are optimal systems to detect the spin state of a few magnetic centers.

Hybrid W-shaped graphene nanoribbons: Distinct electronic and transport properties

We present a first-principles study of electronic and transport properties of a novel W-shaped graphene nanoribbon (W-GNR) structure that comprises hybrid GNR segments with alternating armchair and zigzag edges. Such hybrid W-GNRs exhibit semiconducting characteristics with distinct properties that stem from a unique combination of the features of the armchair and zigzag constituents. When the ribbon is narrow, the interplay of the two GNR components leads to much reduced variation in band gap. The spin-polarized edge states of the zigzag GNR engender an electric-field-driven half-metallicity. Moreover, spin-dependent density of states at the band edge produces asymmetric spin transmission coefficients, yielding unequal spin currents under a large bias voltage. These findings suggest that these new W-GNRs hold great promise for applications in nanoscale spintronic devices.

Coexistence of ferromagnetism and superconductivity in normal mental/superconductor/ferromagnet structures

We extend the Blonder, Tinkham and Klapwijk theory to the study of the inverse proximity effects in the normal mental/superconductor/ferromagnet structures. In the superconducting film, there are the gapless superconductivity and the spin-dependent density of states both within and without the energy gap. It indicates an appearance of the inverse-proximity-effect-induced ferromagnetism and a coexistence of ferromagnetism and superconductivity near the interface. The influence of exchange energy in the ferromagnet and barrier strength at the superconductor/ferromagnet interface on the inverse proximity effects is discussed.

Origin of Magnetic Circular Dichroism in GaMnAs: Giant Zeeman Splitting versus Spin Dependent Density of States

We present a unified interpretation of experimentally observed magnetic circular dichroism (MCD) in the ferromagnetic semiconductor (Ga,Mn)As, based on theoretical arguments, which demonstrates that MCD in this material arises primarily from a difference in the density of spin-up and spin-down states in the valence band brought about by the presence of the Mn impurity band, rather than being primarily due to the Zeeman splitting of electronic states.

Analysis of the Kondo Resonance in a Single Quantum Dot Asymmetrically Coupled to Ferromagnetic Electrodes with Non-Collinear Magnetizations

The Kondo effect is studied theoretically in the framework of the non-equilibrium Green function formalism. The system under consideration consists of a single quantum dot asymmetrically coupled to ferromagnetic electrodes, whose magnetic moments are non-collinear. The spin-dependent density of states, as well as the transport characteristics such as differential conductance and tunneling magnetoresistance through the system are obtained using the equation of motion method. Numerical illustration of the mentioned quantities for several magnetic configurations and coupling strengths is presented and discussed.

Spin-dependent density of states in Ga1−xMnxAs probed by tunneling spectroscopy

We conducted spin-dependent tunneling spectroscopy measurements in Fe∕ZnSe∕Ga1−xMnxAs magnetic tunnel diodes that had a metal-insulator-semiconductor structure. The tunneling magnetoresistance signal in differential conductance spectra (dI∕dV−V) was found to disappear for bias voltages (V) higher than 350meV for a bias direction where electrons tunnel into Ga1−xMnxAs. This indicates that there is exchange splitting in the density of states of Ga1−xMnxAs up to 350meV above the Fermi energy.

Spin-dependent inelastic transport through single-molecule junctions with ferromagnetic electrodes

Using the nonequilibrium Green's function approach and taking into account contributions of both electron and hole, we investigate the spin-dependent carrier transport in a magnetic tunnel junction consisting of a molecular quantum dot coupled to two ferromagnetic leads and to a local vibrational mode. The calculated results show a remarkable influence of electron-phonon interaction and electron-electron interaction on spin-dependent density of states, charge current, and tunneling magnetoresistance (TMR). The oscillating TMR is attributed to the phonon-assisted resonant tunneling rather than the well-known charging effect. The behavior of the zero-bias TMR dip or peak depends to a great degree on whether the quantum dot is in the Kondo or non-Kondo regime.

Effects of FM/NM Interfaces on Spin Accumulation in Free Layer of Pseudo-Spin-Valve Structure

ABSTRACTThe ferromagnetic/nonmagnetic (FM/NM) interfacial effects on the spin accumulation in the free layer were studied in a pseudo-spin-valve structure (PSVs) consisting of two FM layers separated by a NM spacer layer. We developed a spin current model for the current-induced magnetic switching (CIMS) effect based on the spin diffusion equations and appropriate boundary conditions, and derived a new formula for the spin-dependent electrochemical potentials that are related to the spin-dependent density of states. The results indicate that the spin accumulation in the free layer mainly depends on the interfacial spin asymmetry coefficient Ξ?which originates from the spin-dependent interfacial conductance. In the parallel (anti-parallel) configuration of the magnetization direction for the free and fixed layer, the positive (negative) electron current (electrons from the free layer to the fixed layer and vice versa) drives the spin current polarization factor at the interface between the top electrode and the free layer to vary from Ξ? (-Ξ?) to 0, while at the interface between the free layer and the spacer layer the spin current polarization factor vary from Ξ? (0) to Ξ?/2, which means the total spin current polarization factor in the free layer varies from 0 (Ξ?) to Ξ?/2. These results show that the anti-parallel configuration has a less critical switching current than that of the parallel configuration. Thus, we can design PSVs with symmetrical critical current based on the model.

First-principles study of pressure-induced phase transition in the strongly correlated compoundYCrO4

An accurate full-potential density-functional method is used to study zircon-type YCrO4 as a function of pressure. The lattice parameters and oxygen positions of YCrO4 in zircon-type and scheelite-type structures are investigated in theory. It is calculated by considering the on-site Coulomb interaction that a phase transition from the zircon phase to the scheelite phase takes place at a pressure of 2.9 GPa, which is in good agreement with the experimental observation. The bulk moduli evaluated from the Murnaghan equation as the relation of the total energies with unit cell volumes are 121.61 GPa and 141.28 GPa for the zircon phase and the scheelite phase, respectively. From the spin-dependent density of states and the energy bands, it is concluded that YCrO4 is a ferromagnetic insulator with a magnetic moment of about 1 mu(B) per formula for both phases.

Formation of monatomic Fe chains on vicinalCu(111)surfaces: An atomistic view

An accurate full-potential density-functional method is used to study zircon-type YCrO4 as a function of pressure. The lattice parameters and oxygen positions of YCrO4 in zircon-type and scheelite-type structures are investigated in theory. It is calculated by considering the on-site Coulomb interaction that a phase transition from the zircon phase to the scheelite phase takes place at a pressure of 2.9 GPa, which is in good agreement with the experimental observation. The bulk moduli evaluated from the Murnaghan equation as the relation of the total energies with unit cell volumes are 121.61 GPa and 141.28 GPa for the zircon phase and the scheelite phase, respectively. From the spin-dependent density of states and the energy bands, it is concluded that YCrO4 is a ferromagnetic insulator with a magnetic moment of about 1 mu(B) per formula for both phases.

Tight-binding study of the magnetic properties of Mn-doped Ge

A generalized tight-binding bond Stoner model satisfying charge self-consistence is used to study Mn-doped Ge. We fit the tight-binding parameters to first-principles nonmagnetic band structures of zinc blende MnGe, and then calculate the ferromagnetic and antiferromagnetic band structures with the local stoner model. The predicted band structures match the first-principles ferromagnetic and antiferromagnetic calculations of the MnGe well and reveal that the MnGe is a half-metallic ferromagnet with integer magnetic moment in Bohr magneton. Applied to low concentrations of Mn doping, this model produces good magnetic moments, spin-dependent density of states, and energetics for Mn doping concentrations down to 0.03125. These results are in agreement with corresponding first-principles calculations. This method can be applied to other transition-metal doped semiconductors.

Intense terahertz laser fields on a two-dimensional electron gas with Rashba spin–orbit coupling

The spin-dependent density of states and the density of spin polarization of an InAs-based two-dimensional electron gas with the Rashba spin–orbit coupling under an intense terahertz laser field are investigated by utilizing the Floquet states to solve the time-dependent Schrödinger equation. It is found that both densities are strongly affected by the terahertz laser field. Especially a terahertz magnetic moment perpendicular to the external terahertz laser field in the electron gas is induced. This effect can be used to convert terahertz electric signals into terahertz magnetic ones efficiently.