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With the end of Moore's law in sight, researchers are in search of an alternative approach to manipulate information. Spintronics or spin-based electronics, which uses the spin state of electrons to store, process and communicate information, offers exciting opportunities to sustain the current growth in the information industry. For example, the discovery of the giant magneto resistance (GMR) effect, which provides the foundation behind modern high density data storage devices, is an important success story of spintronics; GMR-based sensors have wide applications, ranging from automotive industry to biology. In recent years, with the tremendous progress in nanotechnology, spintronics has crossed the boundary of conventional, all metallic, solid state multi-layered structures to reach a new frontier, where nanostructures provide a pathway for the spin-carriers. Different materials such as organic and inorganic nanostructures are explored for possible applications in spintronics. In this short review, we focus on the boron nitride nanotube (BNNT), which has recently been explored for possible applications in spintronics. Unlike many organic materials, BNNTs offer higher thermal stability and higher resistance to oxidation. It has been reported that the metal-free fluorinated BNNT exhibits long range ferromagnetic spin ordering, which is stable at a temperature much higher than room temperature. Due to their large band gap, BNNTs are also explored as a tunnel magneto resistance device. In addition, the F-BNNT has recently been predicted as an ideal spin-filter. The purpose of this review is to highlight these recent progresses so that a concerted effort by both experimentalists and theorists can be carried out in the future to realize the true potential of BNNT-based spintronics. [ABSTRACT FROM AUTHOR]

Abstract: We have theoretically investigated the conductance and the conductance spin-polarization (P G ) with combined magneto-electric potential structure in monolayer graphene. The results show that P G could be enhanced and hence reach maximum (P G±=±1) no matter which one of the four barrier parameters is increased. These four barrier parameters are the intensity (β) and the width (w) of the magnetic barriers, the intensity (U) and the width (b) of the potential barriers. The above results indicate that it is easy to realize the spin filtering. The peak value of the conductance and its corresponding energy could be controlled by adjusting the corresponding four barrier parameters. Additionally, switching effect and low energy spin-up injection could be realized in the structure under certain specific conditions. [Copyright &y& Elsevier]

Abstract: Using the non-equilibrium Green's function method combined with the density functional theory, we investigate the electron and spin transport properties of carbon chains covalently connected with zigzag-edged graphene electrodes at finite bias with the parallel (P) and antiparallel (AP) magnetism configurations. When two zigzag-edged graphene electrodes are H2–ZGNR–H structures, spin filtering effect can be realized only with AP magnetism configuration. While one electrode is replaced with the H–ZGNR–H structure, we observe a dual spin filtering effect with above two magnetism configurations. But the spin transport properties of carbon chains can also be affected by the linking way of the carbon chain ends. Deeper analyses show that the spin-related properties are related to the electrodes, magnetism configurations, and the connection structure between electrodes and carbon chains. [Copyright &y& Elsevier]

We propose an electron beam lithography system that would allow for pattern transfer from a magnetic reticle to a wafer. The reticle consists of a patterned magnetic media where magnetization of a nanomagnet stores a value of a pixel. Information stored on this media is transferred as a pattern onto the electron-resist via spin-polarized electrons photo-generated from the reticle and spin-filtered along the way to the wafer to generate contrast. It is speculated that such a system offer significantly higher throughput than a multielectron-beam lithography system and may outpace in flexibility, cost and throughput extreme ultraviolet-lithography systems that are currently being developed, while at least matching the resolution of both lithography systems. [ABSTRACT FROM AUTHOR]

The ballistic spin-filter effect from a ferromagnetic metal into a semiconductor has theoretically been studied with an intention of detecting the spin polarizability of density of states in FM layer at a higher energy level. The physical model for the ballistic spin filtering across the interface between ferromagnetic metals and semiconductor superlattice is developed by exciting the spin polarized electrons into n-type AlAs/GaAs superlattice layer at a much higher energy level and then ballistically tunneling through the barrier into the ferromagnetic film. Since both the helicity-modulated and static photocurrent responses are experimentallymeasurable quantities, the physical quantity of interest, the relative asymmetry of spin-polarized tunneling conductance, could be extracted experimentally in a more straightforward way, as compared with previousmodels. The present physical model serves guidance for studying spin detection with advanced performance in the future. [ABSTRACT FROM AUTHOR]

Abstract: The effect of bias voltage on electron tunneling across a junction with a ferroelectric–ferromagnetic composite barrier is investigated theoretically. Because of the inversion symmetry breaking of the spontaneous ferroelectric polarization, bias voltage dependence of the electron tunneling shows significant differences between the positive bias and the negative one. The differences of spin filtering or tunnel magnetoresistance increase with the increasing absolute value of bias voltage. Such direction preferred electron tunneling is found intimately related with the unusual asymmetry of the electrical potential profile in two-phase composite barrier and provides a unique change to realize rectifying functions in spintronics. [Copyright &y& Elsevier]

Abstract: We have theoretically investigated the spin-polarized transport properties of molecular junctions consisting of biradical and triradical organic magnetic molecules sandwiched between two symmetric gold electrodes, respectively. It shows that these junctions function as a spin rectifier or a combination of spin and charge rectifiers with high spin rectification ratios exceeding 100, wherein the spin diode/rectification effect stems from the conjugated length and asymmetry of the molecular framework, which is the pre-requisite for electronic asymmetry of the adsorbed species. The negative differential resistance, spin-filtering and switching properties are also unveiled. In particular, it is revealed that the strong couplings between the electrodes and molecules are responsible for the negative differential resistance. [Copyright &y& Elsevier]

Abstract: The Rashba field in a quantum channel produces spin splitting and population imbalance between spin-up and -down electrons. The channel resistance depends on the alignment between the applied field and the Rashba field because the applied magnetic field causes different mobilities for two types of spins. With an applied field of 2T, the mobility difference between spin-up and -down electrons is 0.75%. [Copyright &y& Elsevier]

Abstract: A spin field effect transistor (spin-FET) using the stray magnetic field induced by ferromagnetic patterns is suggested. Spin polarized electrons are generated by the Zeeman splitting effect at source and selected spins are transmitted by the spin filtering effect at drain. Datta and Das spin transistor needs spin injection and detection in a ferromagnet-semiconductor hybrid junction. This new design has an advantage over the previous spin-FET concept by removing the current flowing at an interface between ferromagnetic metal and semiconductor channel. [Copyright &y& Elsevier]

Abstract: In this paper, we theoretically investigate the effect of the bias and temperature on the electron transport properties in a magnetic nanostructure. It is found that the large spin-polarization can be achieved in such a nanostructure, and the degree of spin-polarization obviously increases with increasing applied bias. It is also found that the conductance curves for the different temperatures obviously intersect at the same Fermi energy for the low Fermi energy, and the degree of spin-polarization decreases with the increase of temperature. Thus, we can control the electron transport through changing the bias and temperature. [Copyright &y& Elsevier]

In this paper, large spin polarization and magnetoconductance in a ferromagnet (FM)/ferromagnetic insulator (FI)/two-dimensional electron gas (2DEG)/non-magnetic insulator (I)/FM hybrid structure are theoretically predicted by introducing a spin-filtering injector. In the framework of coherent tunneling model, the electron transmission probability, spin polarization and magnetoconductance in the hybrid structure all oscillate with the electron density within the 2DEG channel. A complete single-mode spin injection would be realized by designing a well-defined geometry to adjust the competition between the spin-dependent tunneling of the conductive electrons and spin-filtering effect of the FI barrier. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, the bias-dependent electron transport is investigated in detail in a magnetic double-barrier nanostructure in the presence of two bias voltages. It is shown that the large spin-polarization can be achieved in such a nanostructure, and the degree of the spin-polarization is strongly dependent on the applied bias. These interesting properties can provide an alternative scheme to spin-polarize electrons into semiconductors, and this device may be used as a bias-tunable spin filter. [Copyright &y& Elsevier]

Abstract: The spin filtering through Cd1− y Mg y Te/Cd1− x Mn x Te heterostructure, both with zero and with positive zero-field conduction band offset, is investigated theoretically. The magnetic field dependence of the transmission coefficients, current densities, and spin polarizations for considered systems have been studied. It is found that a positive zero-field conduction band offset as high as 3meV shifts considerably the onset of the spin-up complete suppression to lower magnetic field region and thereby unity spin polarization initiates at lower magnetic field. [Copyright &y& Elsevier]

Abstract: We present a theoretical study of spin-dependent electron transport in an antiparallel double -magnetic-barrier nanostructure with an applied bias. It is shown that large spin-polarized current can be achieved in such a device with unidentical strength between two -magnetic-barriers. It also is shown that the degree of electron–spin polarization is strongly dependent upon the applied bias. These interesting properties may provide an alternative scheme to spin-polarize electrons into semiconductors, and this device may be used as a bias-tunable spin filter. [Copyright &y& Elsevier]

The spin-dependent transport of electrons in realistic ferromagnetic/semiconductor hybrid nanosystems was investigated theoretically. This kind of nanosystem can be experimentally realized by depositing a magnetized ferromagnetic strip with arbitrary magnetization direction on the surface of a semiconductor heterostructure. It is revealed that a large spin-polarized current can be achieved in such a device. It is also shown that the spin polarity of the electron transport can be switched by adjusting the structural parameters and location of the ferromagntic strip in the system. These interesting properties may provide an alternative scheme to spin-polarized electrons into semiconductors, and such a nanosystem may be used as a spin filter. [ABSTRACT FROM AUTHOR]

Abstract: We present a theoretical study on the spin-dependent electron transport in a two-dimensional electron gas (2DEG) modulated by a stripe of magnetized ferromagnetic metal under an applied voltage. It is shown that highly spin-polarized current can be achieved in this kind of nanosystems. It is also shown that the spin polarity of the electron transport can be switched by adjusting the applied voltage to the stripe in the device. These interesting properties may provide an alternative scheme to spin-polarize electrons into semiconductors, and this device may be used as a voltage-tunable spin-filter. [Copyright &y& Elsevier]

The spin-dependent electron transport in a two-dimensional electron gas (2DEG) modulated by a stripe of magnetized ferromagnetic metal under an applied voltage was investigated theoretically. It is revealed that highly spin-polarized current can be achieved in this kind of nanosystems. It is also shown that the spin polarity of the electron transport can be switched by adjusting the applied voltage to the stripe in the device. These interesting properties may provide an alternative scheme to spin polarize electrons into semiconductors, and this device may be used as a voltage-tunable spin filter. [ABSTRACT FROM AUTHOR]

Abstract: We present a theoretical study on spin-dependent transport of electrons in any anti-parallel double -magnetic-barrier nanostructure, which can be experimentally realized by depositing a ferromagnetic stripe on the surface of a semiconductor heterostructure. A general fomula of tranmission probability for electrons tunneling through this kind of nanostructures, is obtained. It is shown that large spin-polarized current can be achieved in such a device. It also is shown that the degree of electron-spin polarization is strongly dependent upon magnetic-strength difference of two -barriers. These interesting properties may provide an alternative scheme to spin-polarize electrons into semiconductors, and this device may be used as a tunable spin-filter. [Copyright &y& Elsevier]

Abstract: This article presents a review of the state of the art of materials used in spintronics. It is devoted to materials exhibiting novel and exciting electronic properties: manganites, double perovskites, spinel ferrites and diluted magnetic semiconductors. We present the main features of these classes of materials as well as the most important solid state physics results obtained from them in the field of spintronics. To cite this article: J. Cibert et al., C. R. Physique 6 (2005). [Copyright &y& Elsevier]

Abstract: We study theoretically the spin-dependent electron transport in realistic magnetic-barrier nanostructures, which can be experimentally realized by depositing a magnetized ferromagnetic stripe with arbitrary magnetization direction on the surface of a semiconductor heterostructure. It is shown that highly spin-polarized current can be achieved in this kind of nanostructures. It is also shown that the spin polarity of the electron transport can be switched by adjusting the magnetized angle of the ferromagnetic stripe in the system. These interesting properties may provide an alternative scheme to spin-polarize electrons into semiconductors and may be used as a spin-filter. [Copyright &y& Elsevier]

In this paper, we study the electron transport properties in the double non-collinear δ-magnetic barriers within 2-dimensional electron gas. We find that the transmission of spin current depends on the relative orientation of each magnetic barrier. In addition to the well-known unpolarized configurations in an antiparallel magnetic barrier structure, we also find that there exists infinite unpolarized structures due to the time-reversal symmetry. These structures will be important in the designs of spin valve. [ABSTRACT FROM AUTHOR]

We theoretically investigate the spin-dependent transport properties of electrons in realistic magnetic-electric barrier nanostructures, which are produced by the deposition, on top of a heterostructure, of a metallic ferromagnetic stripe with an applied voltage. The degree of the electron-spin polarization is found to be closely associated with this voltage, although the use of applied voltage itself induces no spin polarization effect. As a positive voltage is applied to the stripe the electron-spin polarization shifts towards the low-energy region and increases; it shifts towards the high-energy direction and reduces for a negative applied voltage. These results shown in this work imply that the degree of electron-spin polarization can be tuned by means of an applied voltage on the stripes of system, which may result in a practical voltage-controlled spin filter. [ABSTRACT FROM AUTHOR]

Abstract: Spin filter devices based on resonant tunneling hybrid magnetic-barrier structures are proposed and spin-dependent transport properties are investigated theoretically. Such a kind of devices can be experimentally realized by depositing two ferromagnetic stripes with different magnetizations on top of two-dimensional electron gas contained in a semiconductor heterostructure. Since these two ferromagnetic stripes induce different magnetic barriers, which leads to the strong dependence of both electronic transmission probability and conductance of device on electronic spins, electrons show up a considerable spin polarization effect. These interesting properties may provide an alternative approach to spin-polarize electrons in semiconductors and may be used as spin filters. [Copyright &y& Elsevier]

One type of combined magnetically modulated nanostructures is proposed that can be experimentally realized by depositing two hybrid ferromagnetic stripes on the surface of a semiconductor heterostructure. Since these two stripes induce different magnetic barriers, the electron transmission and the conductance of nanostructure are strongly dependent upon the electronic spins. Thus, in this kind of hybrid magnetic nanostructures, electrons show up a considerable spin polarization effect, which provides an alternative approach to realization of spin-polarized electrons into semiconductors and may be of practical importance for spin-based nanodevice applications. [ABSTRACT FROM AUTHOR]

In the regime of the quantum-coherent transport the Zeeman splitting in combination with a build up potential barrier can lead to spin filtering. We argue that in one-dimensional systems with relatively strong spin–orbit coupling associated with the inter-facial electric field the filtering depends on the current direction if the magnetic field of the appropriate strength and orientation is applied. [Copyright &y& Elsevier]

We investigate wave-vector filtering and spin filtering for electrons tunneling through a magnetic double-barrier and double-well quantum structure in the presence of an external electric field, where the double magnetic wells are within or outside the double magnetic barriers. It is shown that electronic resonant tunneling shows strong wave-vector-dependent enhancement and suppression as the applied bias increases. It is also shown that although the current density decreases with the strength of the inhomogeneous magnetic field increasing, the degree of spin polarization is generally enhanced and shows a more wider and nearly 100% spin polarization plateau in small external bias range. The general rules for relations between wave-vector filtering and the magnetic configuration as well as between spin filtering and the magnetic configuration are summarized and explained. [Copyright &y& Elsevier]