Spin-down Electrons Research Articles

Thermally driven pure spin current through an interacting quantum dot

We study spin-dependent electron transport properties of a thermally driven interacting quantum dot. When an external magnetic field is applied to the quantum dot, the effective transmissions of spin-up and spin-down electrons are separated from each other and have a perfect mirror symmetry with respect to the incident energy at a certain gate voltage. A pure spin current can be induced in the system and modulated by a magnetic field. Under certain magnetic field strengths, a larger pure spin current can be obtained at gate voltages with the values in a range, not just at a specific voltage. These results indicate that the system can be worked as a pure spin current generator.

Magnetic bipolarity of (8,0)SWCNT functionalized by methyl or light halomethyles

The geometrical, electronic and magnetic properties of (8,0)SWCNT, functionalized by either CH3, CH2F or CH2Cl form this treatise. We employ the density functional theory along with Grimme-D2 approach in spin polarization mode. From the calculated adsorption energies and distances, it is demonstrated that the adsorption of the radicals by (8,0)SWCNT is of chemisorption and exothermic nature. In the adsorption process, spin-down electrons migrate from (8,0)SWCNT to the radicals, giving rise to an exchange splitting. The resulted spin-distinct band structure and densities of states show that the aforementioned compounds behave as bipolar ferromagnetic semiconductors. We, moreover, evaluate the spin-flip energy gaps that demonstrates switchablity of the generated spin-polarized currents. This value turns out to be the smallest for the substance (8,0)SWCNT plus CH2F. According to the range of Fermi energy, for which a substance remains half-metal, it is concluded again that, the manipulation of spin states in compound (8,0)SWCNT plus CH2F is easier when used in the development of spintronic devices. Finally, we also present the compensation temperatures, below which the three substances remain ferromagnetic, indicating that the latter compound is operational up to 231.9 K. The present article, thus provides strong motivation for employing (8,0)SWCNT functionalized by CH2F in spintronic applications.

First Principle Insight into the Structural, Optoelectronic, Half Metallic, and Mechanical Properties of Cubic Perovskite NdInO3

The structural, optoelectronic, magnetic, and elastic properties of cubic perovskite NdInO3 have been analyzed by spin-polarized density functional theory. The computed values of total energies of the optimized systems reveal that ferromagnetic phase is energetically stable rather than paramagnetic phase of cubic NdInO3 compound. Furthermore, the spin-polarized band structure and density of states elucidate the half metallic nature of the studied material due to a different response of both spin channels; spin-up electrons illustrate metallic character, while spin-down electrons display a direct band gap (M–M) semiconducting behavior. The elastic parameters indicate anisotropic and brittle characteristics; further, the total magnetic moment of the cubic NdInO3 perovskite (3 μB) is mainly due to the Nd site with very feeble contribution of In and O atoms. The complete set of optical parameters demonstrate that cubic NdInO3 is active in visible–ultraviolet region. Based on these results, NdInO3 is categorized as a half metallic ferromagnetic compound, which might be used in spintronics and optoelectronic devices.

Structure, magnetic and electronic transport properties in antiperovskite cubic γ′-CuFe3N polycrystalline films

The structure, magnetic and electronic transport properties of the facing-target reactively sputtered polycrystalline CuFe3N films have been investigated systematically. The CuFe3N film has a cubic antiperovskite structure. The saturation magnetization satisfied the modified Bloch's spin wave theory. At 300 K, the saturation magnetization of the 80 nm-thick CuFe3N films is 402 emu/cm3, which is smaller than 800 emu/cm3 of the 80 nm-thick polycrystalline Fe4N films. The CuFe3N films are metallic. The anomalous Hall effect in the “dirty region” of σxx < 104 S/cm can be explained by the intrinsic mechanism and the side jump in the proper scaling, which is similar to Fe4N. However, the sign of magnetoresistances in CuFe3N is opposite to that of Fe4N below 20 K because the doped-Cu affects the competition among the Lorentz force, spin-orbit coupling, weak localization and s-d exchange interaction. The small anisotropic magnetoresistance is dominated by the spin-down conduction electron. The transformation from the two-fold to one-fold symmetry in the planar Hall resistivity of the 10-nm-thick-CuFe3N films is related to the competition between the temperature-dependent charge scattering and magnetic-field-dependent spin scattering.

Molecular Oxygen-Induced Ferromagnetism and Half-Metallicity in α-BaNaO4: A First-Principles Study.

Molecular oxygen resembles 3d and 4f metals in exhibiting long-range spin ordering and strong electron correlation behaviors in compounds. Ferromagnetic spin ordering and half-metallicity, however, are quite elusive and have not been well acknowledged. In this Article, we address this issue by studying how spins will interact with each other if the oxygen dimers are arranged in a different way from that in the known superoxides and peroxides by first-principles calculations. Based on the results of a structure search, thermodynamic studies, and lattice dynamics, we show that tetragonal α-BaNaO4 is a stable half-metal with a Curie temperature at 120 K, the first example in this class of compounds. Like 3d and 4f metals, the O2 dimer carries a local magnetic moment of 0.5 μB due to the unpaired electrons in its π* orbitals. This compound can be regarded as forming from the O2 dimer layers stacking in a head-to-head way. In contrast to the arrangement in AO2 (A = K, Rb, Cs), the spins are ferromagnetically coupled both within and between the layers. Spin polarization occurs in π* orbitals, with spin-up electrons fully occupying the valence band and spin-down electrons partially occupying the conduction band, forming semiconducting and metallic channels, respectively. Our results highlight the importance of geometric arrangement of O2 dimers in inducing ferromagnetism and other novel properties in O2-dimer-containing compounds.

Skyrmion–electron interaction in the separated spin-up and spin-down quantum hydrodynamics approach

Abstract The Berry gauge field associated with adiabatic quantum evolution represents a very interesting area of research, especially for the description of non-relativistic fermions coupled to a skyrmion texture. We construct a quantum hydrodynamics model that describes the electron–skyrmion interactions, with separate descriptions of spin-up and spin-down electrons as two different fluids. The quantum effects, represented by the quantum Bohm potential, are taken into account. We investigate the electron gas moving in a smooth magnetic texture, where the magnetic moments adjust to the local magnetization direction of the skyrmion, and derive the equations of motion and evolution of spin density for two fluids of electrons in the emergent gauge fields. Applying the separated spin evolution quantum hydrodynamics to the 2D electron gas, traveling on the background of the Berry gauge field in plane samples, located in an external magnetic field, we predict a wave of a new kind in the electron gas. This novel wave appears as an influence of emergent fields and quantum effects.

Ultrafast polarization of an electron beam in an intense bichromatic laser field

Here, we demonstrate the radiative polarization of high-energy electron beams in collisions with ultrashort pulsed bi-chromatic laser fields. Employing a Boltzmann kinetic approach for the electron distribution allows us to simulate the beam polarization over a wide range of parameters and determine the optimum conditions for maximum radiative polarization. Those results are contrasted with a Monte-Carlo algorithm where photon emission and associated spin effects are treated fully quantum mechanically using spin-dependent photon emission rates. The latter method includes realistic focusing laser fields, which allows us to simulate a near-term experimentally feasible scenario of a 8 GeV electron beam scattering from a 1 PW laser pulse and provide a measurement that would verify the ultrafast radiative polarization in high-intensity laser pulses that we predict. Aspects of spin dependent radiation reaction are also discussed, with spin polarization leading to a measurable (5%) splitting of the energies of spin-up and spin-down electrons.

Magnetosonic shock waves in magnetized quantum plasma with the evolution of spin-up and spin-down electrons.

The quantum hydrodynamic model is used to study the linear and nonlinear properties of small amplitude magnetosonic shock waves in dissipative plasma with degenerate inertialess spin-up and spin-down electrons and inertial classical ions. Spin effects are considered via spin pressure and macroscopic spin magnetization current. A linear dispersion relation is derived analytically and plotted numerically for different plasma parameters such as spin density, polarization ratio, plasma beta, quantum diffraction, spin magnetization energy, and magnetic diffusivity. Employing the standard reductive perturbation technique, a Korteweg-de Vries-Burgers-type equation is derived for small amplitude waves and studied numerically. We have observed that an oscillatory and monotonic shock waves are generated depending upon the plasma configurations. The phase portraits of both oscillatory and monotonic shock waves are also presented. Interestingly, different plasma parameters are found to play a significant role in the transition of oscillatory to monotonic shock waves or vice versa. Most importantly it is found that, the magnetosonic excitations obtained with spin-up and spin-down electrons are significantly different from the usual electron ion quantum plasma. The work presented is related to magnetosonic waves in dense astrophysical environments such as a pulsar magnetosphere and neutron stars.

Application of magnon coherent states in spintronics

Ferromagnetic resonance (FMR) is a useful method to inject spin current between adjacent layers. At the interface between a ferromagnetic insulator (FMI) and a normal metal (NM), conduction electrons are reflected by a spin-flip scattering absorbing a magnon from the ferromagnetic side. Therefore, a magnon source is fundamental to create an imbalance between up and down-spin conduction electrons close to the interface. Using a combination of static and oscillating magnetic fields, one can generate a precession magnetization that provides the over populated magnon state necessary to inject magnetization by spin pumping. Since magnon coherent states are a suitable method to describe precession magnetization, we used coherent states to study spintronic properties. We determined the spin conductivity as well as the spin current injection in an FM/NM junction.

Half-metal calculations of CoZrGe half-Heusler compound by using generalized gradient approximation (GGA) and modified Becke-Johnson (mBJ) methods

The structural and magnetic calculations of CoZrGe half-Heusler compound were investigated using generalized gradient approximation (GGA) and modified Becke-Johnson potential. First, the volume-energy curves were performed to determine which phase was more stable. According to that curve, the ferromagnetic (FM) phase was more energetically stable than non-magnetic (NM) phase. Then the total density of states and band structures were plotted using GGA and mBJ methods. Since the spin-up and spin-down electrons cut the Fermi energy level, they show metallic properties in the GGA method. Therefore, it is possible to say that CoZrGe half-Heusler compound is a metallic ferromagnetic material when GGA method is used. However, when the mBJ method was used, the band gap was seen around the Fermi energy level in spin up electrons. This showed that spin-up electrons had semiconductor properties and spin-down electrons had metallic nature. Thus, in the mBJ method, CoZrGe half-Heusler compound showed half-metal ferromagnetic nature. The Fermi energy level value in the GGA method was 0.586 Ry, while it was obtained as 0.601 Ry by using the mBJ method. This ensured that the Fermi energy level was higher when the mBJ method was used and the intersections in the GGA method was eliminated. Total magnetic moment is obtained as 1.00 μB/f.u. in both calculation methods. It has been clearly observed that these two different methods affected the Fermi energy level. Finally, CoZrGe half-Heusler compound can be used in spintronic calculations.

Spin magnetoacoustic wave

Spectra of magnetosonic waves are studied by taking account of spin-up and spin-down electrons as two different fluids. It is found that the electron spin effect modifies the dispersions of the perpendicular and obliquely propagating magnetosonic waves even without considering the magnetization current effect. It may be noted that previously the spin effect in these dispersions appeared only due to magnetization. Furthermore, the consideration of separate spin evolution gives rise to the existence of a new spin dependent mode, i.e., spin magnetoacoustic mode along with fast and slow magnetosonic modes. It is also noted that spin polarization reduces the wave frequency of spin magnetoacoustic waves and fast magnetosonic waves while the frequency of the slow mode was slightly affected by these effects. The relevance of the present investigation in the dense astrophysical environments is also pointed out.

Novel room-temperature ferromagnetism in Gd-doped 2-dimensional Ti3C2Tx MXene semiconductor for spintronics

Two-dimensional nanosheets of MXene (Ti3C2) and Gd+3-doped MXene (Ti3C2) have been synthesized superficially by using the cost-effective co-precipitation method. The hexagonal crystal structure doped by Gd was confirmed using X-ray Diffraction. The doping was further confirmed by using scanning electron microscopy, energy dispersive X-ray spectroscopy and Fourier transformed infra-red spectroscopy. Furthermore, UV–Vis spectroscopy absorption spectra, followed by a Tauc-plot, revealed a band-gap value of 1.93 eV for Gd-doped MXene, reduced from that for pure MXene (2.06 eV). The magnetic measurement of undoped and doped MXene indicate a clear ferromagnetic hysteresis existing at room-temperature. The asymmetric spatial spin-density of states (s-DOS) for undoped MXene is attributed to the existence of spin-up and spin-down electrons of Ti-3d atoms at top and bottom Titanium layers. The strength of one of the spin-type (spin-up) increases more than two-folds at room-temperature after the doping of Gd+3 cations due to the fact that it contains more unpaired electrons around Fermi level making the MXene more ferromagnetic. The present report establishes the existence of ferromagnetism introduced by doping of Gd+3 cation in Ti3C2 MXene at room-temperature making it a suitable candidate for two-dimensional spintronic devices operating at room-temperature.

Coherent spin transport through a six-coordinate FeN6 spin-crossover complex with two different spin configurations

Due to the magnetic bistability, single-molecule spin-crossover (SCO) complexes have been considered to be the most promising building blocks for molecular spintronic devices. Here, we explore the SCO behavior and coherent spin transport properties of a six-coordinate FeN $_6$ complex with the low-spin (LS) and high-spin (HS) states by performing extensive first-principles calculations combined with non-equilibrium Green's function technique. Theoretical results show that the LS $\leftrightarrow$ HS spin transition via changing the metal-ligand bond lengths can be realized by external stimuli, such as under light radiation in experiments. According to the calculated zero-bias transmission coefficients and density of states as well as the $I$ - $V$ curves under small bias voltages of FeN $_6$ SCO complex with the LS and HS states sandwiched between two Au electrodes, we find that the examined molecular junction can act as a molecular switch, tuning from the OFF (LS) state to the ON (HS) state. Moreover, the spin-down electrons govern the current of the HS molecular junction, and this observed perfect spin-filtering effect is not sensitive to the detailed anchoring structure. These theoretical findings highlight this examined six-coordinate FeN $_6$ SCO complex for potential applications in molecular spintronics.

Electronic structure and persistent current of hexagonal MoS2 quantum rings: A tight-binding calculations

The electronic structure and the persistent current of the hexagonal MoS2 quantum rings are investigated within the multi-orbital tight-binding formalism. It is shown that the degenerate energy levels split owing to spin-orbit coupling of Mo and S atoms, especially for the highest occupied state. The energy levels show the periodic oscillation with the increase of perpendicular magnetic flux. The spin-up electrons induced by magnetic flux flow clockwise around the rings resulting in paramagnetism. However, the spin-down electrons flow anticlockwise around the rings resulting in diamagnetism. Thus the hexagonal MoS2 quantum rings exhibit paramagnetic or diamagnetic effect, which is the result of competition of spin-up and spin down states.

First-principles calculations on half-metal ferromagnetic results of VZrAs and VZrSb half-heusler compounds and Al1-xMxAs (M= Co, Fe and x = 0.0625, 0.125, 0.25) diluted magnetic semiconductors

The theoretical calculations on structural, electronic, half-metallic and elastic properties of both VZrAs, VZrSb half-Heusler compounds and Al1-xFexAs and Al1-xCoxAs (x = 0.0625, 0.125, 0.25) diluted magnetic semiconductors (DMSs) have been investigated using WIEN2k. In Al1-xFexAs and Al1-xCoxAs (x = 0.0625, 0.125, 0.25) DMSs, the ferromagnetic phases are more stable than non-magnetic and antiferromagnetic phases. In VZr(As, Sb) compounds, the ferromagnetic (FM) phases in Type II structure are more stable energetically. The spin-up electrons of both half-Heusler compounds have semiconducting nature with 0.643 and 0.799 eV energy gaps while spin-down electrons of Al0.875Fe0.125As, Al0.9375Fe0.0625As and Al1-xCoxAs (x = 0.0625, 0.125, 0.25) DMSs have semiconducting feature. The mechanically stability conditions are provided by all compounds except VZrAs half-Heusler compound. Therefore, VZrSb, Al1-xFexAs and Al1-xCoxAs (x = 0.0625, 0.125, 0.25) diluted magnetic semiconductors (DMS) are mechanically stable against the deformation. The VZrAs compound can be deformed in the experimental process since it does not provide the C11 > C12 mechanical stability condition. According to conditions of the ductility or brittleness of polycrystalline material, both VZrAs and VZrSb half-metal compounds are ductile materials while Al1-xFexAs and Al1-xCoxAs (x = 0.0625, 0.125, 0.25) DMSs are brittle. Finally, VZr(As, Sb), Al1-xCoxAs (x = 0.0625, 0.125, 0.25) and Al1-xFexAs (x = 0.0625, 0.125) compounds were obtained true half-metal ferromagnetic materials (HMF) within 4.00, 2.00 and 5.00 μB/f.u.

First principle predictions on half-metallic results of MnZrX (X = In, Tl, C, Si, Ge, Sn, Pb, N, P, As, Sb, O, S, Se, Te) half-Heusler compounds

Abstract The half-metallic calculations of MnZrX (X = In, Tl, C, Si, Ge, Sn, Pb, N, P, As, Sb, O, S, Se Te) half-Heusler compounds were investigated using WIEN2k code. In all compounds, the ferromagnetic (FM) phases were the most stable states energetically. The spin-up electrons of all half-Heusler compounds have semiconducting nature with energy gaps while spin-down electrons have metallic behavior. According to calculated Cij elastic constants, MnZrIn, MnZrTl, MnZrSi, MnZrGe, MnZrSn, MnZrPb, MnZrP, MnZrAs, MnZrSb, MnZrS, MnZrTe half-Heusler compounds are elastically stable except MnZrC, MnZrN and MnZrO compounds. Additionally, MnZr(In, Tl, C, Si, Ge, N, P, As, Sb, S and Se) compounds are ductile and MnZr(Sn, Pb, O and Te) compounds are brittle materials. Finally, MnZr(In, Tl), MnZr(C, Si, Ge, Sn, Pb, O), MnZr(N, P, As, Sb), MnZr(S, Se, Te) half-Heusler compounds were obtained true half-metallic ferromagnets (HMF) within 4.00, 3.00, 2.00 and 1.00 µB/f.u. respectively.

Graphene transport in a parallel magnetic field: Spin polarization effects at finite temperature

Abstract We present an analysis of the temperature and magnetic field dependence of the total electron conductivity in monolayer graphene systems due to screening effects around charged impurities. The evaluation of the two spin channels polarization functions and screening coefficients is based on the random phase approximation (RPA). The total electron conductivity due to both spin-up and spin-down electrons decreases as function of temperature in the low temperature regime, presents a minimum in the intermediate temperature regime, and increases linearly with temperature in the high temperature regime. As function of magnetic field, the system total electron conductivity increases across all temperature regimes.

Spin-Orbit Torque in a Single Ferromagnetic Layer Induced by Surface Spin Rotation

Spin-orbit torque (SOT) has been demonstrated as a promising means to manipulate the magnetization of a ferromagnet in a device, but so far has been observed mainly in systems with broken bulk or structure-inversion symmetry. This study reports the observation of SOT in single Fe${}_{0.8}$Mn${}_{0.2}$ layers. Due to the scattering asymmetry for spin-up and spin-down electrons, the torques from the top and bottom surfaces simply add up instead of canceling each other out, which effectively removes the requirement for spatial-inversion asymmetry in generating SOT. This means SOT can be created in a ferromagnet without the need for an additional nonmagnetic layer.

Dirac Electron Behavior for Spin-Up Electrons in Strongly Interacting Graphene on Ferromagnetic Mn5Ge3.

An elegant approach for the synthesis of graphene on the strong ferromagnetic (FM) material Mn5Ge3 is proposed via intercalation of Mn in the graphene-Ge(111) interface. According to the density functional theory calculations, graphene in this strongly interacting system demonstrates the large exchange splitting of the graphene-derived π band. In this case, only spin-up electrons in graphene preserve the Dirac-electron-like character in the vicinity of the Fermi level and the K point, whereas such behavior is not detected for the spin-down electrons. This unique feature of the studied gr-FM-Mn5Ge3 interface that can be prepared on the semiconducting Ge can lead to its application in spintronics.

Electrical detection of current generated spin in topological insulator surface states: Role of interface resistance

Current generated spin polarization in topological insulator (TI) surface states due to spin-momentum locking has been detected recently using ferromagnet/tunnel barrier contacts, where the projection of the TI spin onto the magnetization of the ferromagnet is measured as a voltage. However, opposing signs of the spin voltage have been reported, which had been tentatively attributed to the coexistence of trivial two-dimensional electron gas states on the TI surface which may exhibit opposite current-induced polarization than that of the TI Dirac surface states. Models based on electrochemical potential have been presented to determine the sign of the spin voltage expected for the TI surface states. However, these models neglect critical experimental parameters which also affect the sign measured. Here we present a Mott two-spin current resistor model which takes into account these parameters such as spin-dependent interface resistances, and show that such inclusion can lead to a crossing of the voltage potential profiles for the spin-up and spin-down electrons within the channel, which can lead to measured spin voltages of either sign. These findings offer a resolution of the ongoing controversy regarding opposite signs of spin signal reported in the literature, and highlight the importance of including realistic experimental parameters in the model.