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The single-phase bismuth ferrite BiFeO 3 (BFO) has garnered significant interest due to its spintronic-based switching properties observed at room temperature. The first-principles calculations were executed to examine the spin-polarized electronic, dielectric, and structural characteristics of co-doped BFO with lanthanum (La) at A-site and cobalt (Co), nickel (Ni) at B-site in its hexagonal phase (Bi 1-α La α Fe 1-β Ni β O 3 with α = β = 0.04) with generalized gradient approximation (GGA-PBE). The highest value (1.01 × 10−11 A) of total current observed in La Ni co-doped BFO, featuring a distinct spin current of the same magnitude, attributed to spin polarization at the Fermi level (100 %). Additionally, Co-doped BFO exhibits the highest observed spin current density (1.05 × 109A/m2) and charge current density (1.03 × 10−5A/m2). In case of dielectric switching properties, the Ni-doped BFO displays the lowest values of linear dielectric polarization (6.00 × 10−2 C/m2), polarization charge at its interface (1.27 × 10−17 C), capacitance (4.23 × 10−15 F), and switching energy (3.81 × 10−19 J), which is particularly lower than the reported switching energy (1.92 aJ) of multiferroic capacitor. [ABSTRACT FROM AUTHOR]

Micromagnetics is a continuum theory describing magnetization patterns inside ferromagnetic media. The dynamics of a ferromagnetic material are governed by the Landau-Lifshitz equation. This equation is highly nonlinear and has a non-convex constraint. In this work, a finite element approximation of a current-induced magnetization dynamics model is proposed. The model consists of a modified Landau-Lifshitz-Gilbert (LLG) equation incorporating spin transfer torque. The scheme preserves a non-convex constraint, requires only a linear solver at each time step and is easily applicable to the limiting cases. As the time and space steps tend to zero, a proof of convergence of the numerical solution to a (weak) solution of the modified LLG equation is given. Numerical results are presented to show the effect of the injected current on magnetization switching. [ABSTRACT FROM AUTHOR]

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In this paper, an analysis is made of the physical processes that occur in the spinvalve structures during the recording or reading of bits in high-speed magnetic memory devices using the phenomenon of moment transfer by spin-polarized current. Mathematical models of the phenomenon of magnetic resistance for magnetite / non-magnetic metal / magnet structures and phenomena that occur when the free layer is reversed under the influence of a spin-polarized current are presented. The analysis of the effect on the magnetoresistive effect of the spin-valve structure of the ratio of the thickness of the free and fixed layers are provided. The effect on the magnetoresistive effect in the spin-valve structure of the ratio of the thickness of ferromagnetic layers with small and large coercive forces (free and fixed layer) is investigated. It is shown that for high values of the polarization coefficient, the increase in the thickness of the fixed layer results in an undesired decrease in the magnetoresistive effect. [ABSTRACT FROM AUTHOR]

Highlights • A spin current generator in a single molecular magnet is realized. • The spin-related currents are studied by Hubbard operator Green’s function method. • The system can generate spin-polarized current or pure spin current. • Two configurations of spin bias are considered and they show different features. Abstract In this paper we study the spin- and charge-transport behaviors of a single molecular magnet (SMM) coupled to external reservoirs with spin-dependent chemical potentials. By using the Hubbard operator Green’s function method, we show that in the limit of a pinned macrospin the SMM can serve as an effective spin current filter or generator. Two configurations of spin bias are considered. For SMM coupled with symmetric dipolar spin bias, the system can generate spin-polarized current and pure spin current by adjusting the relative magnitude of spin bias and Coulomb interaction. It originates from the competition of two spin-opposite transport channels. Also due to this competition, one can observe a negative differential spin conductance. For SMM coupled with asymmetric dipolar spin bias, the system can only generate spin-polarized currents. The SMM as a spin current generator shows features different from the usual quantum dot system and these features can be useful in molecular spintronics. [ABSTRACT FROM AUTHOR]

As microwave signal generators, the spin transfer nano-oscillator (STNO) based on magnetic skyrmion has attracted huge interest recently. However, the circular magnetic skyrmion-based oscillator only produces a microwave signal with a single oscillation frequency, and detecting the precession of skyrmion in the entire nanodisk is also a challenge. In the paper, we propose an STNO based on elliptical skyrmion, which can simultaneously generate a single frequency or multiple frequency oscillation signal, and the oscillation frequency also can be increased to some extent. Moreover, to reduce the difficulty of detection, the method to restrict elliptical skyrmion moving in a specific orbit is suggested. Our results provide a possible candidate to design the spintronic devices. [ABSTRACT FROM AUTHOR]

In a two dimensional electron system (2DES), coherent spin precession of a ballistic spin polarized current, controlled by the Rashba spin orbit interaction, is a remarkable phenomenon that’s been observed only recently. Datta and Das predicted this precession would manifest as an oscillation in the source-drain conductance of the channel in a spin-injected field effect transistor (Spin FET). The indium arsenide single quantum well materials system has proven to be ideal for experimental confirmation. The 2DES carriers have high mobility, low sheet resistance, and high spin orbit interaction. Techniques for electrical injection and detection of spin polarized carriers were developed over the last two decades. Adapting the proposed Spin FET to the Johnson-Silsbee nonlocal geometry was a key to the first experimental demonstration of gate voltage controlled coherent spin precession. More recently, a new technique measured the oscillation as a function of channel length. This article gives an overview of the experimental phenomenology of the spin injection technique. We then review details of the application of the technique to InAs single quantum well (SQW) devices. The effective magnetic field associated with Rashba spin-orbit coupling is described, and a heuristic model of coherent spin precession is presented. The two successful empirical demonstrations of the Datta Das conductance oscillation are then described and discussed.

Stuart Parkin of IBM's Almaden Research Centre came up with the concept of spintroncs-based memory that has no moving parts, but in which the information moves. Racetrack memory stores digital data in the magnetic domain walls of nanowires. The bits of information, which are stored in the wire using the spin of electrons rather than an electronic charge, would be moved around at several hundred meters per second, using a spin polarized current. Adjacent bits would be delineated from one another via domain walls with magnetic vortices. This technology promises to yield information storage devices with high reliability, performance and capacity. [ABSTRACT FROM AUTHOR]

Abstract: Rectangular Au/Co/Au/Bi2Sr2CaCu2O8+ δ (Bi2212) mesa structures with large areas and high thicknesses were fabricated on as-grown Bi2212 single crystals in order to obtain small critical current from as-grown mesas by the injection of spin polarized current and so eliminate the adjustment of doping level for successful THz emission. We have performed c-axis resistance versus temperature (R–T), current–voltage (I–V) characteristics and bolometer measurements. It is the first time that THz emission has been observed from as-grown mesas due to injection of spin polarized current. [Copyright &y& Elsevier]

Abstract: We theoretically study spin-polarized current through a single electron tunneling transistor (SETT), in which a quantum dot (QD) is coupled to non-magnetic source and drain electrodes via tunnel junctions, and gated by a ferromagnetic (FM) electrode. The I–V characteristics of the device are investigated for both spin and charge currents, based on the non-equilibrium Green''s function formalism. The FM electrode generates a magnetic field, which causes a Zeeman spin-splitting of the energy levels in the QD. By tuning the size of the Zeeman splitting and the source–drain bias, a fully spin-polarized current is generated. Additionally, by modulating the electrical gate bias, one can effect a complete switch of the polarization of the tunneling current from spin-up to spin-down current, or vice versa. [Copyright &y& Elsevier]

To investigate the effect of polarized current on tunneling characteristics of intrinsic Josephson junctions (IIJs), spin-polarized and spin-degenerate current have been injected through the c-axis of HgBr2 intercalated Bi2.1Sr1.5Ca1.4Cu2O8+δ (Bi2212) single crystals on which 10 x 10 μm2 mesas have been fabricated. These two spin conditions are achieved by depositing either Au (15 nm)/Co (80 nm)/Au (156 nm) multilayers or single Au film on HgBr2 intercalated Bi2212 with Tc = 74 K followed by photolithography and Ar ion beam etching. The I-V characteristics have been measured with and without a magnetic field parallel to c-axis at 4.2 K. A fine, soft Au wire is used to make a gentle mechanical contact on the top of a particular mesa in the array. Tunneling conductance characteristics were obtained and the magnetic field dependence of sumgap voltage peaks was investigated. These peaks do not change in position with increasing magnetic field for both contact configurations. In addition, the temperature dependence of tunneling characteristics of the IJJs are obtained and existence of pseudogap feature is observed above Tc for HgBr2 intercalated Bi2212. [ABSTRACT FROM AUTHOR]

By analogy with the classic effect of the double refraction of light, we investigate the relevant effect of an electron entering from the Non-Rashba region to the Rashba region in two-dimensional systems. It is shown that the effect of electronic double refraction is determined by a combined parameter γ = m * λ F α/2 πħ2, rather than both the Rashba coefficient α and wavelength λ F of a Fermi electron, separately. For the case of normal incidence, the analytical expressions for the wavefunction of the electron are presented; it is predicted that the Rashba spin-orbit coupling can induce a current perpendicular to the normal incident direction of the electron. Moreover, the general case of incident electron with any given momentum and spin state are studied numerically in detail, including the abrupt changes of spin direction and the two-step characters for reflection. [ABSTRACT FROM AUTHOR]

Abstract: This article provides a review of our results on nanostructurization of lead telluride, PbTe. This IV–VI group narrow-gap semiconductor exhibits paraelectric behaviour leading to a huge dielectric constant at helium temperatures. Because the Coulomb potential fluctuations produced by charged defects are strongly suppressed in PbTe nanostructures, one can reach the quantum ballistic regime at significantly relaxed conditions in comparison with other systems. In particular, we observe precise zero-field conductance quantization in the wires made of modulation doped PbTe/PbEuTe quantum wells where the heavily doped layer is separated from the conducting channel only by a 2nm thick spacer layer. The second important property is the very large Zeeman splitting. It reaches 4meV/T. Accordingly, significant spin splitting of the conductance plateaux is observed already at fields below 1T. Therefore, the system is attractive for the construction of local spin filters. We show that the presence of metal layers does not impair the quantum ballistic properties. Furthermore, we have developed a new method of tuning the PbTe nanostructures, using laterally placed metallic electrodes. We have found that this method is more effective than previous schemes using used p–n junctions and it provides better stability of the nanostructures. [Copyright &y& Elsevier]

Abstract: We numerically investigate the spin polarization of the current induced by Rashba spin–orbit coupling in three-terminal mesoscopic devices in two dimensional electron system (2DES). The spin-dependent transmission probabilities are calculated by the recursive Green function method. It is found that generally high spin polarization can be obtained at certain resonant energies. In the case of strong spin–orbit coupling, the effect of the spin on the motion of an electron is not negligible. A propagating electron is deflected due to the Lorentz force by spin–orbit induced effective magnetic field. [Copyright &y& Elsevier]

This paper deals with micromagnetic model of magnetization reversal in nano scale-point contact devices driven by nonuniform injection of a spin-polarized current. A computational study of the magnetization reversal in the nanosecond regime will be presented considering the influence of the current density distribution below the aperture region on the reversal time. For high current values, a strong dependence of the reversal time on the current distribution has been observed. Finally, results of micromagnetic simulations show that the reversal time versus current behaviour (at T = OK) is monotonic, very different from the switching processes observed in standard spin valves and magnetic tunnel junctions with uniform current injection. [ABSTRACT FROM AUTHOR]

We present a theoretical study of charge and spin resolved currents in a Y-shape molecular junction which consists of phenalene molecule at the center of junction connected to three graphene nanoribbons as external leads by using Green's function method. We show that by applying exchange magnetic field and choosing proper geometry of the structure, the pure spin and fully spin polarized currents could be obtained in one of the external leads. Also, by choosing appropriate strength of exchange magnetic field, it is possible to split a totally unpolarized incoming current into up and down spin currents transmitting through different output leads. Moreover, in some conditions, the molecular junction shows a negative differential resistance behavior for both charge and spin currents. • Phenalene molecular Y-shape junction with three graphene nanoribbons. • Study of spin-dependent electron current using Green function method. • Achieving pure spin current in a certain voltage in one of the external terminals. • In proper voltage range a fully spin polarized current obtained. • An Unpolarized incoming spin current is split into up and down spin currents. [ABSTRACT FROM AUTHOR]