Spin Filtering Efficiency Research Articles

Electron spin filtering by thin GaNAs/GaAs multiquantum wells

Effectiveness of the recently discovered defect-engineered spin-filtering effect is closely examined in GaNAs/GaAs multiquantum wells (QWs) as a function of QW width. In spite of narrow well widths of 3–9 nm, rather efficient spin filtering is achieved at room temperature. It leads to electron spin polarization larger than 18% and an increase in photoluminescence intensity by 65% in the 9 nm wide QWs. A weaker spin filtering effect is observed in the narrower QWs, mainly due to a reduced sheet concentration of spin-filtering defects (e.g., Gai interstitial defects).

One-dimensional organometallic V–anthracene wire and its B–N analogue: efficient half-metallic spin filters

Using density functional theory, we have investigated the structural, electronic and magnetic properties of infinitely periodic organometallic vanadium-anthracene ([V(2)Ant](infinity)) and [V(4)(BNAnt)(2)](infinity) (where BNAnt is B-N analogue of anthracene) for their possible application in spintronics. From our calculations, we find that one-dimensional [V(2)Ant](infinity) and [V(4)(BNAnt)(2)](infinity) wires exhibit robust ferromagnetic half-metallic and metallic behavior, respectively. The finite sized V(6)Ant(2) and V(6)(BNAnt)(2) clusters are also found to exhibit efficient spin filter properties when coupled to graphene electrodes on either side.

Fabrication of a Spin-filter Device with Co Ferrite

A magnetic tunnel junction (MTJ) spin-filter device of Pt/Co ferrite/MgO/Co demonstrated -19.8 % tunnel magnetoresistance (TMR) and 27.5% spin-filter efficiency at 10 K. By increasing the bias voltage, the TMR at 10 K first increased and then decreased, exhibiting a maximum at 0.17 V. This anomalous dependence of TMR on bias was interpreted as tunneling via the spin-down conduction band in the Co ferrite. At room temperature (RT), the tunneling mechanism was thought to originate from hopping in the defect states due to structural and chemical defects in the Co ferrite. To achieve higher spin-filter effect at RT, it is important to reduce the defects in the Co ferrite barrier.

Spin-polarized transport and thermopower of organometallic nanocontacts

We present a theoretical study of the length dependence of both conductance and thermopower of organometallic vanadium-benzene molecules (V n Bz n+1 ) sandwiched between magnetic Co(100) electrodes. We show that the molecules with n≥3 are efficient spin filters. Namely, we find that the zero bias conductance of the majority electrons is small and decays exponentially with increasing length of the molecule and is in the tunneling regime while the minority electrons show metallic conductance. We show furthermore that the thermopower strongly depends on the length of the molecules and can even change sign as a function of length and temperature.

Spin filter due to spin Hall effect with axially asymmetric potential

We examine a three-terminal spin filter including an artificial potential created by antidot, scanning tunnel microscope (STM) tip, etc., fabricated on semiconductor heterostructures with strong spin–orbit interaction. When the potential is attractive and its strength is properly tuned, the resonant scattering takes place, which enhances the extrinsic spin Hall effect. As a result, the efficiency of the spin filter can be more than 50% when the potential is axially symmetric. The efficiency becomes smaller when the symmetry is broken, but we still expect an efficient spin filter unless the degree of asymmetry is too large.

Enhanced spin Hall effect by tuning antidot potential: Proposal for a spin filter

We propose an efficient spin filter including an antidot fabricated on semiconductor heterostructures with strong spin-orbit interaction. The antidot creates a tunable potential on two-dimensional electron gas in the heterostructures, which may be attractive as well as repulsive. Our idea is based on the enhancement of extrinsic spin Hall effect by resonant scattering when the attractive potential is properly tuned. Numerical studies for three- and four-terminal devices indicate that the efficiency of the spin filter can be more than 50% by tuning the potential to the resonant condition.

Efficient organometallic spin filter based on Europium-cyclooctatetraene wire

Electronic structures, magnetic, and transport properties of organometallic sandwich molecular wire (SMW) constructed with altering europium (Eu) atoms and cyclooctatetraene (COT) rings have been studied by spin-polarized first-principles calculations and nonequilibrium Green’s function method. The one-dimensional Eu-COT SMW is predicted to be a ferromagnetic semiconductor. The calculated average magnetic moment per Eu atom is about 7μB. The total magnetic moment (TMM) of Eun(COT)n+1(n=1–4) sandwich clusters increases linearly with the number of Eu atoms and the linear relation TMM=7n-2 holds, which agrees nicely with experimental observations. The spin transportation calculations show that Eu-COT clusters coupled to gold electrodes are nearly perfect spin filters. In addition, we find that this large transmission spin polarization is very robust regardless of the contact configuration of the junctions, which is very important for the future molecular spintronics.

Manipulating Spin Transport via Vanadium−Iron Cyclopentadienyl Multidecker Sandwich Molecules

Electronic spin transport through (CpFeCpV)n multidecker wire sandwiched between magnetic nickel (Ni) electrodes is simulated in the linear response regime based on DFT. We studied the effects of the molecule−electrode contact and molecule wire length on its spin filter behavior. The amplitude and the sign of the spin filter efficiency can be manipulated by choosing the contact condition (e.g., anchoring groups, absorbing positions on Ni electrodes surface). The performance of the spin filter can be further manipulated by adjusting the length of the molecule wire. Various ways to realize nearly perfect spin-filter are illustrated.

Room-temperature defect-engineered spin filter based on a non-magnetic semiconductor

Generating, manipulating and detecting electron spin polarization and coherence at room temperature is at the heart of future spintronics and spin-based quantum information technology. Spin filtering, which is a key issue for spintronic applications, has been demonstrated by using ferromagnetic metals, diluted magnetic semiconductors, quantum point contacts, quantum dots, carbon nanotubes, multiferroics and so on. This filtering effect was so far restricted to a limited efficiency and primarily at low temperatures or under a magnetic field. Here, we provide direct and unambiguous experimental proof that an electron-spin-polarized defect, such as a Ga(i) self-interstitial in dilute nitride GaNAs, can effectively deplete conduction electrons with an opposite spin orientation and can thus turn the non-magnetic semiconductor into an efficient spin filter operating at room temperature and zero magnetic field. This work shows the potential of such defect-engineered, switchable spin filters as an attractive alternative to generate, amplify and detect electron spin polarization at room temperature without a magnetic material or external magnetic fields.

Organometallic vanadium-borazine systems: efficient one-dimensional half-metallic spin filters

Download options Please wait... Article information DOI https://doi.org/10.1039/B810089F Article type Paper Submitted 16 Jun 2008 Accepted 24 Oct 2008 First published 28 Nov 2008 Download Citation J. Mater. Chem., 2009,19, 1761-1766 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions Organometallic vanadium-borazine systems: efficient one-dimensional half-metallic spin filters S. S. Mallajosyula, P. Parida and S. K. Pati, J. Mater. Chem., 2009, 19, 1761 DOI: 10.1039/B810089F To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Search articles by author Sairam S. Mallajosyula Prakash Parida Swapan K. Pati

Influence of oxidation on the spin-filtering properties ofCoFe2O4and the resultant spin polarization

We report the direct measurement of spin polarization in epitaxial ${\text{CoFe}}_{2}{\text{O}}_{4}$ tunnel barriers using the Meservey-Tedrow technique. By observing an asymmetry in the Al quasiparticle density of states in $\text{Pt}(111)/{\text{CoFe}}_{2}{\text{O}}_{4}(111)/\ensuremath{\gamma}{\text{-Al}}_{2}{\text{O}}_{3}(111)/\text{Al}$ tunnel junctions, we prove the existence of spin filtering in our ${\text{CoFe}}_{2}{\text{O}}_{4}$ tunnel barriers. We further analyze the effect of oxidation conditions during film growth on the polarization of the tunneling current, revealing an important role played by oxygen vacancies in the spin-filter efficiency of this material.

Magnetic Properties of EuS/Co Multilayers on KCl and BaF₂ Substrates

EuS/Co multilayers are hybrid structures composed of a model ferromagnetic semiconductor EuS (Curie temperature Tc=16.5 K) and a ferromagnetic transition metal Co. Recent investigations of these multilayers revealed variety of important spintronic effects, such as an antiferromagnetic interlayer coupling in EuS/Co bilayers [1] and a very efficient spin filtering by EuS electron barrier in Al/EuS/Co tunneling structures [2]. These effects are expected to originate from the exchange interactions across EuSCo interface. In previous studies, polycrystalline or amorphous EuS/Co multilayers were grown on glass or on Si substrate with Pt/Co metallic buffer layer. In this work, we exploit the technological method developed for the epitaxial growth of EuS/PbS multilayers on KCl and BaF2 substrates, in order to study the magnetic properties of EuS/Co multilayers with monocrystalline EuS layer. EuS/Co/EuS trilayers and Co/EuS bilayers were grown on cleaved KCl (001) and BaF2 (111) substrates using high vacuum deposition technique employing electron guns for Co and EuS. Epitaxial 20-60 nm thick PbS buffer layer was deposited on the substrates from heated tungsten boat. The layer thickness covered the range 35-55 A for EuS and 40-250 A for Co. The structural properties of the layers were examined by xray diffraction method revealing monocrystalline PbS buffer and bottom EuS layer. Co and top EuS layers are expected to be polycrystalline. Magnetic properties of the layers were examined using magneto-optical Kerr (MOKE) and superconductor (SQUID) magnetometry techniques. In the case of MOKE experiments, the linearly polarized light from He-Ne laser was used in longitudinal MOKE geometry. Measurements of magnetic hysteresis loops were performed in temperature range T = 4-250 K and in external magnetic fields up to 2 kOe applied in the plane of the multilayer. All the investigated multilayers showed ferromagnetic properties at room temperature due to Co layer with the ferromagnetic transition in EuS layer clearly marked upon cooling below 16 K. In EuS/Co/EuS trilayers grown on KCl substrate the antiferromagnetic alignment of magnetization vectors of Co and EuS layers was experimentally observed as a characteristic low field plateau on magnetic hysteresis loops and a decrease of multilayer magnetization below 16 K. In contrast, no interlayer coupling was found in multilayers grown on BaF2 substrate. In Co/EuS bilayers, the characteristic temperature dependent shift of the magnetic hysteresis loops was found indicating the well known exchange bias effect. We assign this experimental finding to the exchange coupling between Co layer and an ultrathin (about 2 nm) top antiferromagnetic CoO layer known to spontaneously form on Co layers in the air.

Fano and Dicke effects in a double Rashba-ring system

The electronic transport in a system of two quantum rings side-coupled to a quantum wireis studied via a single-band tunneling tight-binding Hamiltonian. We derivedanalytical expressions for the conductance and spin polarization when the rings arethreaded by magnetic fluxes with Rashba spin–orbit interaction. We show that byusing the Fano and Dicke effects this system can be used as an efficient spinfilter even for small spin–orbit interaction and small values of magnetic fluxes.We compare the spin-dependent polarization of this design and the polarizationobtained with one ring side-coupled to a quantum ring. As a main result, wefind better spin polarization capabilities as compared to the one-ring design.

Spin-orbital Kondo decoherence by environmental effects in capacitively coupled quantum dots

Strong correlation effects in a capacitively coupled double quantum-dot setup were previously shown to provide the possibility of both entangling spin-charge degrees of freedom and realizing efficient spin-filtering operations by static gate-voltage manipulations. Motivated by the use of such a device for quantum computing, we study the influence of electromagnetic noise on a general spin-orbital Kondo model and investigate the conditions for observing coherent, unitary transport crucial to warrant efficient spin manipulations. We find a rich phase diagram where low-energy properties sensitively depend on the impedance of the external environment and geometric parameters of the system. Relevant energy scales related to the Kondo temperature are also computed in a renormalization-group treatment, allowing us to assess the robustness of the device against environmental effects. These are minimized at low bias voltage and for highly symmetric devices concerning the geometry.

Efficient spin filtering in a disordered semiconductor superlattice in the presence of Dresselhaus spin–orbit coupling

The influence of the Dresselhaus spin–orbit coupling on spin polarization by tunneling through a disordered semiconductor superlattice was investigated. The Dresselhaus spin–orbit coupling causes the spin polarization of the electron due to transmission possibilities difference between spin up and spin down electrons. The electron tunneling through a zinc-blende semiconductor superlattice with InAs and GaAs layers and two variable distance In x Ga (1− x ) As impurity layers was studied. One hundred percent spin polarization was obtained by optimizing the distance between two impurity layers and impurity percent in disordered layers in the presence of Dresselhaus spin–orbit coupling. In addition, the electron transmission probability through the mentioned superlattice is too much near to one and an efficient spin filtering was recommended.

A spin polarizer made of a diluted magnetic semiconductor quantum well

In this work we present results for the transport properties of a spin polarizer consisting of a resonant tunneling diode (RTD) in which the well is made of Ga 1 - x Mn x As . This is a diluted magnetic semiconductor (DMS) of p type. The magnetization of the well produces a splitting of the valence band of approximately 0.15 eV and consequently a splitting of resonant peaks. This 0.15 eV separation is bigger than the one produced by the highest stationary magnetic field obtained in a laboratory. As a consequence we get a spin polarized current when only one of these peaks is in between the Fermi level and the top of the valence band. We have considered heavy hole (HH) and light hole (LH) bands. The last one had not been considered in our previous works. Our system is described by a tight-binding Hamiltonian. The carriers interaction is calculated in the Hartree approximation. The charge distribution of the system and the potential profile are calculated self-consistently. Our results show that the system works as a very efficient spin filter. The magnetism and charge neutrality is mainly due to heavy holes. For a system with wide barriers, the spin polarized current is mainly due to light holes.

Design of an efficient spin filter device

In a quantum dot in which the spin degeneracy of a carrier is lifted, the Fano effect may be used as an effective means to generate spin polarization of transmitted carriers. In this work, we propose a new and more effective design of a spin-dependent polarizer. The proposed device consists of a quantum wire with two side-coupled quantum dots. A detailed analysis of the spin-dependent polarized current is carried out, and we find some improvements as compared to more conventional designs.

A selfconsistent calculation of the transport properties of a double barrier spin filter

A double barrier resonant tunneling device in which the well is made of a semi-magnetic material can work as an efficient spin filter. Today it is possible to make semiconductors that are ferromagnetic at room temperature. Therefore the device studied here has a great potential to be used as a polarizer, an analyzer and other spintronic applications. We discuss here the case of a Ga1-xMn xAs/Ga1-yAl yAs system because it can be integrated into the well known AlGaAs/GaAs technology. Our tight-binding Hamiltonian includes the kinetic energy, the double-barrier profile, the electric field, the magnetic term, the hole-impurity and the hole-hole interactions. The profile and the charge distribution are calculated self-consistently. In previous works we studied this system by solving the Hamiltonian in the reciprocal space, in order to simplify the treatment of the Poisson equation for the charge distribution. Here we introduce a simple one dimensional Green function that permits to solve all terms in the real space. Besides, a real space renormalization formalism is used to calculate exactly the electronic currents for each spin polarization. The results confirm that the proposed system is a good device for spintronics.

La 2 ∕ 3 Sr 1 ∕ 3 MnO 3 – La 0.1 Bi 0.9 MnO 3 heterostructures for spin filtering

We have grown heterostructures associating half-metallic La2∕3Sr1∕3MnO3 (LSMO) bottom electrodes and ferromagnetic La0.1Bi0.9MnO3 (LBMO) tunnel barriers. The layers in the heterostructures have good structural properties and top LBMO films (4 nm thick) have a very low roughness when deposited onto LSMO∕SrTiO3(1.6nm) templates. The LBMO films show an insulating behavior and a ferromagnetic character that are both preserved down to very low thicknesses. They are thus suitable for being used as tunnel barriers. Spin-dependent transport measurements performed on tunnel junctions defined from LSMO∕SrTiO3∕LBMO∕Au samples show a magnetoresistance of up to ∼90% at low temperature and bias. This evidences a spin-filtering effect by the LBMO layer, with a spin-filtering efficiency of ∼35%.

Spin filtering through ferrimagnetic NiFe2O4 tunnel barriers

We report experiments of spin-filtering through ultrathin insulating layers of the high Curie temperature ferrimagnetic oxide NiFe2O4 (NFO). The spin-filtering efficiency of electrons tunneling from a gold electrode through NFO is analyzed with a counter-electrode of La2∕3Sr1∕3MnO3 (LSMO). We measure a tunnel magnetoresistance of 40%–50% when the configuration of the magnetizations of the NFO and LSMO goes from parallel to antiparallel. This value corresponds to a spin-filtering efficiency of up to 22% by the NFO barrier. We discuss the sign and temperature dependence of the spin-filter effect and argue that our results show the potential of spinel ferrites for spin-filtering and injection.