Papers by Keyword: Spin Filter

Abstract: In this work, we report the electronic transport properties of an atomic carbon chain sandwiched between two ferromagnetic zigzag graphene nanoribbon electrodes with symmetrical nitrogen-vacancy defects using the density functional theory combining with the non-equilibrium Green’s function method. Our results show that a perfect spin filter is observed with almost 100% spin polarization. Moreover, we also see the negative differential resistance effect from the spin-up current under a low positive voltage bias. These results may promise potential applications in spintronic devices with multi-function in the future.

Abstract: The transport properties of transition metal atoms interfered alpha-graphyne nanoribbon systems are investigated by first-principles calculations combined with the Keldysh nonequilibrium Green’s method. In all, five types of configurations are considered. We find that intervention of three Cr atom in alpha-graphyne nanoribbon systems decreases the conductivity of the system. Further study show that the magnetic direction of the electrode infulence the spin filtering effect greatly, while the ralative magnetic direction of the three transition Cr atoms have little effect on the transport properties. At finite bias window, negative differential resistance happens. Proper analysis are given to explain the spin filtering phenonmenon and the different transport properties via transmission coefficient and projected density of states.

Abstract: Spintronic devices will play a very important role in future information technology. In this study, By spin-polarized density-functional theory calculations combined with the Keldysh nonequilibrium Green’s method, the effect of the spin direction of Co atom in Co- phthalocyanine molecule in modulating spin filtering effects under external biases are investigated. Here, an individual single molecule Co-phthalocyanine is sandwiched between two infinite 8-zigzag-graphene nanoribbon electrodes. we find that the spin direction of the Co atom relative to the magnetic polarization of the left and right electrodes can improve the spin filtering effect greatly. when the polarization direction of the two electrodes is antiparallel and the polarization of Co atom in the Co-phthalocyanine molecule upward, the configuration posesses almost perfectly spin-filter effect. The underlying mechanism of the perfect spin filtering action is applied.

Abstract: The spin-polarized transport is investigated in a magnetic tunnel junction which consists of two ferromagnetic electrodes separated by a magnetic barrier and a nonmagnetic metallic spacer placed in distance above the two dimensional electron gas (2DEG) in presence of an inhomogeneous external modulated magnetic field and a perpendicular wave vector dependent effective potential. Based on the transfer matrix method and the nearly-free-electron approximation the dependence of the conductance and spin polarization on the Fermi energy of the electrons are studied theoretically the. strong oscillations with large amplitude investigated in spin polarization in terms of the Fermi energy due to the inhomogeneous magnetic field. The conductance in terms of the Fermi energy shows no oscillation in low energy but has a strong pick in middle region. this results may be useful for the development of spin electronic devices based on coherent transport, or may be used as a tunable spin-filter.

Abstract: We have analyzed the spin-filtering effects of the electron current in asymmetric ZnSe/Zn1-xMnxSe multilayer structures, under the influence of both an external magnetic field and a bias voltage. In this type of semiconductor systems, conduction band electrons interact with 3d electrons of the magnetic Mn2+ ions. Because of this sp-d exchange interaction, an external magnetic field modulates the effective potential profile seen by spin-up and spin-down electrons, giving rise to a large Zeeman effect. It is found that the degree of spin polarization changes significantly when the electrical bias is switched from forward to reverse, thus the proposed structure displays obvious behavior of spin-filter diode. This originates from the effective “lifting” of the potential for spin-up electrons, which tunnel through actual potential barriers. Structural parameters optimization, with the goal of maximizing the spin-filtering coefficient, was performed by using simulated annealing algorithm. The described effect may be important for designing new tunable spin-based multifunctional semiconductor devices.