Search

We theoretically investigate the dwell time for electrons in an antiparallel double $\delta $ -magnetic-barrier nanostructure, which is constructed on the surface of the InAs/Al x In1- x As heterostructure by patterning two ferromagnetic (FM) stripes. It is shown that the dwell time is dependent on electron spins due to the spin–field interaction between spins and magnetic fields. It is also shown that both magnitude and sign of the spin polarization in the dwell time can be modulated by the structural width or magnetic-strength difference between two magnetic barriers, which may give rise to a controllable temporal spin splitter for spintronics device applications.

The 1-D nanoscale structures are studied with a potential relief containing magnetic barriers separated by nonmagnetic quantum wells in the absence of exchange interaction between the magnetic moments of adjacent barriers. The considered structure is the sequence of N barriers divided into two “ferromagnetic domains” of the length n and N - n-1, both having parallel internal fields. In contrast, the internal field of the nth barrier is not coplanar with respect to the internal fields of the left and/or right “domains.” The degree of spin polarization of an electron wave transmitted through this system is calculated with the assumption that the incident wave is unpolarized with the degree of its polarization equals zero. It is shown that the degree of polarization of the transmitted wave as a function of the impulse exhibits a sequence of sufficiently wide plateaus, which are close to unity. In particular, there are significant deviations from the known spintronics phenomena found earlier in this system such as the valve, filter, and giant magnetoresistance effects. This circumstance provides opportunities for managing the transport properties of the system by varying the noncoplanar degrees of freedom of the system.

Motivated by the experimental isolation of graphene [1], intense investigations have been paid the physical properties of the two-dimensional (2D) honeycomb lattice. Graphene is regarded as a promising material for spintronic applications due to its weak spin-orbit coupling and long spin lifetimes [2]. Up to now, several groups have studied the spin transport properties in graphene with magnetic and electrostatic modulation potentials [3]. How to get efficient spin filtering is one of the research focuses for the application of spintronics. In this work, we investigate spin-dependent bandgap structures and spin filtering in graphene with multiple ferromagnetic barriers. It is shown that the spin-up and spin-down electrons possess different bandgap structures in the case of oblique incidence. As a result, full spin polarization can be achieved within several separated energy intervals. The width of the energy interval with full spin polarization can be effectively manipulated by adjusting the strength of the exchange field. Correspondingly, conductance steps with full spin polarization are observed in the systems. Our investigations may have potential applications in the design of carbon-based spin filters.

The idea of utilizing the electron spin in semiconductor devices leads to the growth of the field semiconductor spintronics. This may result in the development of novel electronic devices with advantages over conventional electronics. However, the basic requirements necessary in developing semiconductor spintronic devices are the efficient generation/injection of spins (or spin current) in/into a semiconductor such that they can be transported reliably, i.e., without spin relaxation, over reasonable distances and, finally, detection of them. Since in spintronic devices, the information is carried by the electron spin, an electrical means of detecting spin current in semiconductors is desirable for fully exploring the possibility of utilizing spin degree of freedom and for possible device applications. Here, I describe an experiment which detects the spin current electrically in semiconductors by investigating the effect of a longitudinal electric field on the spin-polarized electrons generated by a circularly polarized light. The experiment observes the effect as a pure anomalous Hall voltage resulting from non-equilibrium magnetization induced by the spin-carrier electrons accumulating at the transverse edges of the sample as a result of asymmetries in scattering for spin-up and spin-down electrons in the presence of spin-orbit interaction. The results are presented by discussing the dominant spin relaxation mechanisms in semiconductors, and in relation with the recent understanding in this area.

Spin Hall effects convert charge currents into spin currents and vice versa even in nonmagnetic conductors due to spin orbit coupling. This enables spin Hall effects to be utilized both for the generation and detection of spin currents and magnetization dynamics. This paper reviews the experimental characterization of these effects in metallic systems, which have so far shown the highest efficiency in using spin Hall effects for charge-to-spin interconversion. The advantages and disadvantages of complimentary measurement techniques are discussed and in addition an outlook of the possible impact on applications is presented.

We microscopically derive the spin-transfer torque due to diffusive spin current arising from nonequilibrium spin accumulation as realized in systems with nonlocal spin valve structure. Spin relaxation effects in spin transport is taken into account by introducing magnetic impurities.

A transfer matrix method for simulating spin injection into semiconductors in the case of high electric fields has been developed. The nonlinear relationship between electron spin density and electrochemical potential splitting, the effect of electric field on spin diffusion lengths, and spin polarized drift current are accounted for. Using this approach, high magnetoresistance (MR) at high electric fields is predicted. This is due to spin accumulation reaching its extreme values for fermion statistics. This effect opens up a new direction for solving the problem of low MR that semiconductor spintronic devices are facing.

Conduction electron can carry a flow spin angular momentum, a spin current. This paper describes another type of spin current: a spin current carried by spin waves. Some types of spin waves can carry a spin current, which can propagate both in insulators and metals. These two types of spin currents were found to exchange each other at a Pt/Y3Fe5O12 interface.

We theoretically study the spin-dependent transport of conduction electrons across typical metal/semiconductor (SC)/metal structures, where the SC channel exhibits Rashba spin-orbit coupling (SOC) and the metal contacts do not. The spatial discontinuity of the Rashba SOC is shown to result in highly localized, effective magnetic field barriers at the device interfaces. As a result, electrons with oppositely polarized spins along the injection direction are found to be transmitted with different probabilities, resulting in a finite spin polarization. The value of the spin polarization depends sensitively on the Rashba SOC strength within the SC channel, which is well known to be adjustable by an applied gate bias. Thus the proposed structure could be useful as a tunable source of spin-polarized current in spintronic applications.

GaAs-based spin LEDs were used to study spin injection through a Schottky barrier from a ferromagnetic contact formed by an in-situ technique. Optical measurements were performed in both oblique Hanle and Faraday geometry. In addition to direct recombination at the Gamma-point in the quantum well, emission peaks were seen due to phonon-assisted recombination from the X and L valleys in the semiconductor. The presence of the phonon replica peaks indicates that strong tunneling occurs from the Fe into the X and L minima at the interface. As measured in the oblique Hanle geometry, the satellite peaks display optical polarization, which indicates spin polarized injection into these minima. It is argued that enhanced tunneling into the X and L minima leads to a lower spin polarization in the device due to the transport properties of these valleys. This mechanism then limits the maximum effective spin polarization that can be achieved at a coherent interface.

We numerically study the spin-dependent transmission characteristic of conduction electrons across a semiconductor-based trilayer structure with k 3-Dresselhaus spin-orbit coupling, where the Fermi level of electrons exceeds the electrostatic barrier height. Unlike previous studies which focus on the tunneling regime, the electron transmission across our structure is high, thereby ensuring that the polarization can be utilized in a practical device. The polarization is studied for two barrier materials, GaSb and InSb, which both show a considerable polarization amplitude attainable within realistic modeling values. We finally propose two interesting spintronic device concepts based on our structure and its unique polarization characteristics; a sensitive, gate-tunable spin filter and a novel spin transistor device.