Spin-dependent Transmission Probability Research Articles

The study of transport properties in rough ferromagnetic semiconductor rough junctions

The effect of self-affine interface roughness on spin filter tunnelling as a function of interface roughness parameters and the temperature dependent barrier parameters at low biases is studied. The interface roughness is described by the k-correlation model and in terms of self-affine scaling by root-mean-square (rms) deviation Δ, correlation length ξ, and the roughness exponent H(0≤H≤1). In general, the spin-dependent transmission probability is strongly sensitive to roughness and reduced for the case of spin up and down directions in all configurations. Our numerical results show that the roughness affects spin polarization (SP) and tunnelling magnetoresistance (TMR) at different temperatures and decreases the maximum achievable TMR and SP.

The interfacial roughness effect on spin-dependent transport in nonplanar junctions with double magnetic barriers

In this paper, we use the transfer matrix method to study the effect of roughness with nonplanar interfaces on spin-dependent transport properties in a magnetic tunnel junction, which consists of two ferromagnetic semiconductor barriers separated by a nonmagnetic (NM) layer. This trilayer is sandwiched between two NM electrodes. The roughness is modeled as a periodic corrugation interface. Based on the effective mass approximation, the spin-dependent transmission probability, and also the dependence of tunnel magnetoresistance (TMR) and electron spin polarization (SP) on the center nonmagnetic layer quantum well width are studied, theoretically, at several different temperatures. The numerical results show that the SP and TMR have an oscillatory behavior as a function of NM layer thickness and the interface roughness/islands degrade the transmission probability. Our results may be useful for the development of nanoelectronic devices.

A theoretical study of a spin polarized transport and giant magnetoresistance: The effect of the number of layers in a magnetic multilayer

This study presents a quantum-mechanical free electron model for analyzing a spin polarized transport and current-perpendicular-to-the-plane giant magnetoresistance (CPP-GMR) in a more realistic way. The CPP-GMR is evaluated by using three spin resolved conductance parameters based on the Landauer conductance formula. In a ballistic regime, a transfer-matrix method is used to calculate the spin dependent transmission probability as a function of the transverse mode. A spin dependent conduction band structure is constructed by extracting parameters of the free electron model, such as the atomic magnetic moments and the conduction electron densities, from the spin dependent layer-decomposed density of states of the Cu and Co interfacial layers in a Cu5/Co11 slab; these calculations are derived from the density functional theory. As a result, this study shows that the CPP-GMR in a [Cu(5ML)∕Co(11ML)]n magnetic multilayer (n=2–5) with a 35ML×35ML cross section is in the range of 60%–111%. It is qualitatively comparable to the calculation results of first principles. This study also uses transmission probability to explain the increase of spin dependent scattering and CPP-GMR as a function of the number of layers in the [Cu∕Co]n magnetic multilayer. Moreover, the study confirms that modification of the free electron model by quantum-mechanical methods can be applied to calculations of a spin polarized transport and CPP-GMR in a specific material system.

Spin-polarization induced by Rashba spin–orbit coupling in three-terminal devices

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.

Spin polarization in a T-shaped conductor induced by strong Rashba spin-orbit coupling

We investigate numerically the spin polarization of the current in the presence of Rashba spin-orbit interaction in a T-shaped conductor proposed by A.A. Kiselev and K.W. Kim (Appl. Phys. Lett. {\bf 78} 775 (2001)). The recursive Green function method is used to calculate the three terminal spin dependent transmission probabilities. We focus on single-channel transport and show that the spin polarization becomes nearly 100 % with a conductance close to $e^{2}/h$ for sufficiently strong spin-orbit coupling. This is interpreted by the fact that electrons with opposite spin states are deflected into an opposite terminal by the spin dependent Lorentz force. The influence of the disorder on the predicted effect is also discussed. Cases for multi-channel transport are studied in connection with experiments.

Spin-dependent conductance in nonmagnetic InGaAs asymmetric double barrier devices

The spin dependence of the conductance of an asymmetric double-barrier InGaAs device is studied within the multiband k¢p and envelope function approximations. The spin-dependent transmission probability for electrons across the structure is obtained using transfer matrices and the low bias conductance per unit area is calculated as a function of the Fermi energy (or doping) in the contacts. The possibility to obtain spin polarized currents in such devices is demonstrated, however, the resulting degree of polarization is rather small (a few percent) in the specific InGaAs structures considered here.

Electron spin–orbit split minibands in semiconductor asymmetric superlattices

Semiconductor superlattices can be either symmetric or asymmetric with respect to specular reflection along the growth direction. The electronic miniband structure of asymmetric superlattices is in general spin dependent, due to spin‐orbit interaction. Using Kane’s kip model for the bulk and standard envelope function formalism, we have calculated the spin dependent transmission probability for electrons crossing different III‐V politype multibarrier nanostructures. We have obtained spin dependent intervals of energy with nonzero transmission, corresponding to the minibands of allowed electronic states in the superlattice. Spin‐orbit split minibands for InGaAs superlattices, with asymmetric double barrier unit cells and different pairs of latticematched barrier materials, are obtained from the transmission and reflection coefficients for the unit cell. The miniband structure is well reproduced by the transfer matrix calculation with already three unit cells. The symmetric‐asymmetric crossover as well as the miniband formation from the double barrier spin split resonances were also investigated. The effect of electron spin polarization by resonant tunneling is shown to be enhanced with the use of multibarrier or superlattice structures.

Spin injection into ballistic layers and resistance modulation in spin field-effect transistors

The problem of electron transport through low-dimensional ballistic electron layers contacted to ferromagnetic leads is studied theoretically. Using the drift-diffusion approach to describe the potential distribution in the leads, we derive the general expression for the device resistance in terms of both the spin polarization in the leads and partial spin-dependent transmission probabilities. It is found that, due to the dimensionality mismatch between the leads and low-dimensional layer, the resistance depends rather on the total transmission probability T than on the spin polarization in the leads. We calculate T for both two-dimensional (2D) and 1D layers in order to investigate the efficiency of the current modulation in the field-effect and magnetoresistance measurements. The results are compared with recent experimental data.

Spin-polarized scanning tunnelling microscopy: the sensitivity of the spin-dependent current asymmetry to the barrier shape

The influence of the barrier shape on tunnelling of spin-polarized electrons through a vacuum gap between the tip of a scanning tunnelling microscope and a magnetic sample is analysed. It is shown that the spin-dependent transmission probability of the electrons depends strongly on the form of the barrier at the sample surface. This suggests that for a detailed interpretation of the images obtained by a spin-polarized scanning tunnelling microscope the barrier shape should be known.