Spin-dependent diffraction at ferromagnetic/spin spiral interface

Spin-dependent transport is investigated in ballistic regime through the interface between a ferromagnet and a spin spiral. We show that spin-dependent interferences lead to a new type of diffraction called "spin-diffraction". It is shown that this spin-diffraction leads to local spin and electrical currents along the interface. This study also shows that in highly non homogeneous magnetic configuration (non adiabatic limit), the contribution of the diffracted electrons is crucial to describe spin transport in such structures

Does Giant Magnetoresistance Survive in Presence of Superconducting Contact?

The giant magnetoresistance (GMR) of ferromagnetic bilayers with a superconducting contact (F1/F2/S) is calculated in ballistic and diffusive regimes. As in spin-valve, it is assumed that the magnetization in the two ferromagnetic layers F1 and F2 can be changed from parallel to antiparallel. It is shown that the GMR defined as the change of conductance between the two magnetic configurations is an oscillatory function of the thickness of F2 layer and tends to an asymptotic positive value at large thickness. This is due to the formation of quantum well states in F2 induced by Andreev reflection at the F2/S interface and reflection at F1/F2 interface in antiparallel configuration. In the diffusive regime, if only spin-dependent scattering rates in the magnetic layers are considered (no difference in Fermi wave-vectors between spin up and down electrons) then the GMR is supressed due to the mixing of spin up and down electron-hole channels by Andreev reflection.Comment: 7 pages, 4 figures, submitted to Phys.Rev.Let

Spin blockade in ferromagnetic nanocontacts

Using a free-electron model and a linear response theory we investigate spin-dependent electronic transport in magnetic nanocontacts in the ballistic regime of conduction. We emphasize the fact that in atomic-size ferromagnetic contacts it is possible to achieve the conductance value of e2/h, which implies a fully spin-polarized electric current. We explore some consequences of this phenomenon. In particular, we show that the presence of a nonmagnetic region in the nanocontact separating two ferromagnetic electrodes can lead to a spin blockade resulting in very large values of magnetoresistance

Anomalous and Spin Hall Effects in a Magnetic Tunnel Junction with Rashba Spin-Orbit Coupling

Anomalous and spin Hall effects are investigated theoretically for a magnetic tunnel junction where the applied voltage produces a Rashba spin-or bit coupling within the tunneling barrier layer. The ferromagnetic electrodes are the source of the spin-polarized current. The tunneling electrons experience a spin-orbit coupling inside the barrier due to the applied electrical field. Charge and spin Hall currents are calculated as functions of the position inside the barrier and the angle between the magnetizations of the electrodes. We find that both charge and spin Hall currents are located inside the barrier near the in terfaces. The dependence of the currents on magnetic configuration of the magnetic tunnel junction makes possible the manipulation by the Hall currents via rotation of the magnetization of the electrodes.Comment: 10 pages, 4 figure

Influence of s-d interfacial scattering on the magnetoresistance of magnetic tunnel junctions

We propose the two-band s-d model to describe theoretically a diffuse regime of the spin-dependent electron transport in magnetic tunnel junctions (MTJ's) of the form F/O/F where F's are 3d transition metal ferromagnetic layers and O is the insulating spacer. We aim to explain the strong interface sensitivity of the tunneling properties of MTJ's and investigate the influence of electron scattering at the nonideal interfaces on the degradation of the TMR magnitude. The generalized Kubo formalism and the Green's functions method were used to calculate the conductance of the system. The vertex corrections to the conductivity were found with the use of "ladder" approximation combined with the coherent-potential approximation (CPA) that allowed to consider the case of strong electron scattering. It is shown that the Ward identity is satisfied in the framework of this approximation that provides the necessary condition for a conservation of a tunneling current. Based on the known results of ab-initio calculations of the TMR for ballistic junctions, we assume that exchange split quasi-free s-like electrons with the density of states being greater for the majority spin sub-band give the main contribution to the TMR effect. We show that, due to interfacial inter-band scattering, the TMR can be substantially reduced even down to zero value. This is related to the fact that delocalized quasi-free electrons can scatter into the strongly localized d sub-band with the density of states at the Fermi energy being larger for minority spins compared to majority spins. It is also shown that spin-flip electron scattering on the surface magnons within the interface leads to a further decrease of the TMR at finite temperature.Comment: REVTeX4, 20 pages, 9 figures, 1 table, submitted to Phys.Rev.B; In Version 2 the text is substantially improved, the main results and conclusions left the sam

Description of current-driven torques in magnetic tunnel junctions

A free electron description of spin-dependent tranport in magnetic tunnel junctions with non collinear magnetizations is presented. We investigate the origin of transverse spin density in tunnelling transport and the quantum interferences which give rise to oscillatory torques on the local magnetization. Spin transfer torque is also analyzed and an important bias asymmetry is found as well as a damped oscillatory behaviour. Furthermore, we investigate the influence of the s-d exchange coupling on torque in particular in the case of half-metallic MTJ in which the spin transfer torque is due to interfacial spin-dependent reflections

Aharonov-Bohm oscillations and spin transport in a mesoscopic ring with a magnetic impurity

We present a detailed analysis of the Aharonov-Bohm (AB) interference oscillations manifested through transmission of an electron in a mesoscopic ring with a magnetic impurity atom inserted in one of its arms. The spin polarization transport is also studied. The electron interacts with the impurity through the exchange interaction leading to exchange spin-flip scattering. Transmission in the spin-flipped and spin-unflipped channels are explicitly calculated. We show that the entanglement between electron and spin-flipper states lead to a reduction of AB oscillations in spite of absence of any inelastic scattering. The spin-conductance (related to spin-polarized transmission coefficient) is asymmetric in the flux reversal as opposed to the two probe conductance which is symmetric under flux reversal. We point out certain limitations of this model in regard to the general notion of dephasing in quantum mechanics.Comment: 6 pages RevTeX, 9 eps figures included, enlarged version of cond-mat/000741