Spin Filtering Effect Research Articles

Modeling of Spin Transport in Hybrid Magnetic Tunnel Junctions for Magnetic Recording Applications

We have demonstrated modeling of phonon and defect-induced spin relaxation length (LS) in Fe3O4 and organic semiconductor (OSC) Alq3. LS of Alq3 decreases with enhanced disorder and film thickness at a low film width regime. Exponential change of LS at low width regime is found for Alq3 which is, however, absent for Fe3O4 indicating comparable spin-dependent scattering and LS in Fe3O4. LS also decreases with spin-flip probability both for Alq3 and Fe3O4. Voltage-dependent tunnel magnetoresistance (TMR) response in Fe3O4/Alq3/Co and La0.7Sr0.3MnO3 (LSMO)/Alq3/Co hybrid magnetic tunnel junction (MTJ) devices has been attributed to modified spin filter effect across magnetic/OSC junction at high bias regime. TMR reduction with Alq3 thickness for Fe3O4 device has been attributed to spin relaxation at the organic spacer layer. A low bias peak from differential TMR indicates spin-polarized injection for both MTJ devices. Enhanced in-plane spin transfer torque for both MTJ is associated with modified spin filtering at magnetic/OSC junctions. Lower TMR signal for LSMO device indicates reduced tunneling and enhanced carrier injection across the OSC, which is also supported by the band structure profile. The TMR response observed from simulation results matches well with previously reported experimental results. Higher TMR response for Fe3O4 device indicates the possibility of device employment in room temperature magnetic recording applications.

Spin filtering effect in intrinsic 2D magnetic semiconductor Cr2Ge2Te6

All van der Waals Fe3GeTe2/Cr2Ge2Te6/graphite magnetic heterojunctions have been fabricated via mechanical exfoliation and stacking, and their magnetotransport properties are studied in detail. At low bias voltages, large negative junction magnetoresistances have been observed and are attributed to spin-conserving tunneling transport across an insulating Cr2Ge2Te6 layer. With increasing bias, a crossover to Fowler–Nordheim tunneling takes place. The negative sign of the tunneling magnetoresistance suggests that the bottom of a conduction band in Cr2Ge2Te6 belongs to minority spins, opposite to the findings of some first-principles calculations. This work shows that the vdW heterostructures based on 2D magnetic insulators are a valuable platform to gain further insight into spin polarized tunneling transport, which is the basis for pursuing high performance spintronic devices and a large variety of quantum phenomena.

Spin filtering effect in all-van der Waals heterostructures with WSe2 barriers

Exploiting the spin degree of freedom to store and manipulate information provides a paradigm for future microelectronics. The development of van der Waals (vdW) heterostructures has created a fascinating platform for exploring spintronic properties in the two-dimensional (2D) limit. Transition-metal dichalcogenides such as tungsten diselenide (WSe2) have electronic band structures that are ideal for hosting many exotic spin–orbit phenomena. Here, we report the spin-filtering effect in all-vdW heterostructures with WSe2 barrier. Combining 2D-perpendicular magnetic anisotropy Fe3GeTe2 (FGT) with different thicknesses of WSe2, the FGT/WSe2/FGT spin valve shows distinct charge and spin transport behavior. Moreover, the negative magnetoresistance (−4.3%) could be inverted into positive magnetoresistance (up to +25.8%) with decreasing the WSe2 thickness. Furthermore, we proposed a spin-filtering model based on Δ-symmetry electrons tunneling to explain the crossover from negative to positive MR signal through ab initio calculation. These experimental and theoretical results illustrate the rich potential of the families of TMDC materials to control spin currents in 2D spintronic devices.

Almost Perfect Spin Filtering in Graphene-Based Magnetic Tunnel Junctions.

We report on large spin-filtering effects in epitaxial graphene-based spin valves, strongly enhanced in our specific multilayer case. Our results were obtained by the effective association of chemical vapor deposited (CVD) multilayer graphene with a high quality epitaxial Ni(111) ferromagnetic spin source. We highlight that the Ni(111) spin source electrode crystallinity and metallic state are preserved and stabilized by multilayer graphene CVD growth. Complete nanometric spin valve junctions are fabricated using a local probe indentation process, and spin properties are extracted from the graphene-protected ferromagnetic electrode through the use of a reference Al2O3/Co spin analyzer. Strikingly, spin-transport measurements in these structures give rise to large negative tunnel magneto-resistance TMR = −160%, pointing to a particularly large spin polarization for the Ni(111)/Gr interface PNi/Gr, evaluated up to −98%. We then discuss an emerging physical picture of graphene–ferromagnet systems, sustained both by experimental data and ab initio calculations, intimately combining efficient spin filtering effects arising (i) from the bulk band structure of the graphene layers purifying the extracted spin direction, (ii) from the hybridization effects modulating the amplitude of spin polarized scattering states over the first few graphene layers at the interface, and (iii) from the epitaxial interfacial matching of the graphene layers with the spin-polarized Ni surface selecting well-defined spin polarized channels. Importantly, these main spin selection effects are shown to be either cooperating or competing, explaining why our transport results were not observed before. Overall, this study unveils a path to harness the full potential of low Resitance.Area (RA) graphene interfaces in efficient spin-based devices.

TPV radical-based multifunctional molecular spintronic device: A first-principles study

We design a multifunctional molecular spintronic device consisting of two 1,3,5-triphenylverdazyl (TPV) radicals with carbon nanotube bridge and electrodes , and investigate its spin-polarized transport properties using the first-principles density functional theory and nonequilibrium Green's function method. The results show that the spin-polarized transport properties depend strongly on the external magnetic field modulation and high-efficiency spin-filtering, giant magnetoresistance , spin-rectifying and low-bias voltage negative differential resistance effects can be realized in this designed device. The mechanisms are proposed for these interesting physical effects based on the bias-dependent spin-resolved transmission function, projected density of states and corresponding molecular projected self-consistent Hamiltonian orbitals analysis. These results hold great potential for the development of high-performance multifunctional molecular spintronic devices. High-efficiency spin-filtering, giant magnetoresistance, spin-rectifying and low-bias voltage negative differential resistance effects are realized in a TPV radical-based molecular spintronic device with carbon nanotube bridge and electrode. • Spin-polarized transport properties of a TPV radical-based molecular spintronic device are investigated. • Spin-polarized transport properties depend strongly on the external magnetic field modulation. • High-efficiency spin-filtering, GMR, spin-rectifying and low-bias voltage NDR effects are realized.

Trans-polyacetylene based organic spin valve for a multifunctional spin-based device: A first principle analysis

Carbon-based materials are the promising candidates for the design of multifunctional spintronic devices, owing to their fascinating inherent attributes such as the ballistic transport nature, long spin coherence time, etc. Here, we report the spin-dependent electron transport properties of a trans-polyacetylene channel sandwiched between two semi-infinite hydrogen-passivated zigzag graphene nanoribbon (ZGNR) electrodes within the framework of spin-polarized density functional theory (DFT) and non-equilibrium Green's function (NEGF) formalisms. The proposed device exhibits an excellent spin-dependent transport behavior within the bias window of [-0.5 V, 0.5 V]. In parallel configuration (PC), the device offers an ideal spin filtration efficiency of almost 100% within the bias range of [-0.4 V, 0.4 V], and in antiparallel configuration (APC), it exhibits negative differential resistance (NDR), dual-spin rectification, and dual-spin filtration effects. Also, a high tunnel magnetoresistance (TMR) of 1.2× 10 5 % is achieved. To validate the aforementioned effects, the transmission spectra along with the area enclosed by the curve, eigenvalues, eigenstates, and quantum conductance have also been analyzed. In addition, the impact of hybridization and torsion defects on the spin-dependent transport phenomenon through trans-polyacetylene has been investigated. Furthermore, the modelled device is observed to exhibit the spin Seebeck effect in PC under the influence of temperature gradient. The proposed device may stand as a good contender for various spintronic and spin caloritronic applications. • First principle based analysis of a trans-polyacetylene based multifunctional spin-based device. • The device displays a perfect spin filtration efficiency and dual rectification effects. • A high tunnel magnetoresistance (TMR) of 1.2× 10 5 % is achieved. • Thermal Spin Seebeck and spin filtering effects are observed in the proposed model. • A potential candidate in the field of spintronic and spin caloritronic applications.

Spinterface Effects in Hybrid La0.7Sr0.3MnO3/SrTiO3/C60/Co Magnetic Tunnel Junctions.

Orbital hybridization at the Co/C60 interface been has proved to strongly enhance the magnetic anisotropy of the cobalt layer, promoting such hybrid systems as appealing components for sensing and memory devices. Correspondingly, the same hybridization induces substantial variations in the ability of the Co/C60 interface to support spin-polarized currents and can bring out a spin-filtering effect. The knowledge of the effects at both sides allows for a better and more complete understanding of interfacial physics. In this paper we investigate the Co/C60 bilayer in the role of a spin-polarized electrode in the La0.7Sr0.3MnO3/SrTiO3/C60/Co configuration, thus substituting the bare Co electrode in the well-known La0.7Sr0.3MnO3/SrTiO3/Co magnetic tunnel junction. The study revealed that the spin polarization (SP) of the tunneling currents escaping from the Co/C60 electrode is generally negative: i.e., inverted with respect to the expected SP of the Co electrode. The observed sign of the spin polarization was confirmed via DFT calculations by considering the hybridization between cobalt and molecular orbitals.

Spin transport properties and nanodevice simulations of NiI2 monolayer

Two-dimensitional (2D) magnetic semiconducting materials attract extensive interest in recent years. A new type of magnetic semiconducting nickel-based transition metal diiodide-NiI2 monolayer (NiI2-ML) was successfully prepared in recent experiments. Some nanodevices based on the NiI2-ML are designed and their spin-resolved transport and photoelectric properties are studied. Strong rectification and spin filtering effects are observed in the NiI2-ML pn-junction. The NiI2-ML pin-junction shows a field-effect property. Moreover, it is found that NiI2-ML has a strong response to green light that promotes its phototransistor to generate exploitable photocurrent. The results of this paper show that NiI2-ML is a multifunctional magnetic semiconducting material with potential applications in the fields of spintronic and optoelectronic devices.

Multifunctional molecular spintronic device based on zigzag-edged trigonal graphene: A first-principles study

A zigzag-edged trigonal graphene (ZTG)-based molecular spintronic device is proposed and its spin-polarized transport properties are investigated using a first-principles method based on density functional theory in conjunction with nonequilibrium Green's function technique. Multiple high-efficiency physical effects, including spin-filtering, giant magnetoresistance, spin-rectifying and low-bias voltage negative differential resistance effects, are observed in the proposed system. The underlying mechanisms are analyzed by the bias voltage-dependent spin-resolved transmission spectra, projected density of states and local density of states. The results indicate that the proposed system has great potential in developing high-performance multifunctional molecular spintronic devices.

Spin Interference Effects in a Ring with Rashba Spin-Orbit Interaction Subject to Strong Light–Matter Coupling in Magnetic Field

Electron transport through a one-dimensional quantum ring, subjected to Rashba spin–orbit interaction and connected with two external leads, is studied in the presence of external fields. They include the optical radiation, produced by an off-resonant high-frequency electric field, and a perpendicular magnetic field. By means of the Floquet theory of periodically driven quantum systems the interference effects under these fields are described in detail. It is found analytically the specific conditions to reach the spin-filtering effect, caused by the interplay of the external fields and Rashba spin-orbit interaction.

Study of the transport properties of cobalt atomic contact under mechanical strain in a nitrogen atmosphere

Achieving an efficient spin-filter effect and large magneto-resistance in molecular junctions is very important in spintronics. By employing the non-equilibrium Green's function formalism combined with the density functional theory, this study investigated the atomic structures and spin-resolved transport properties of molecular junctions consisting of nitrogen (N2) sandwiched between two cobalt (Co) electrodes with different crystal lattices as a function of stretching distance. In the case of face-centred cubic Co electrodes, our calculations showed that the transport properties depend strongly on the stretching process, which changes the contact between the N2 and Co electrodes. Specifically, the maximum spin polarization is due to the configuration of N2 molecules sitting in parallel with the protruding Co atoms. Furthermore, the Co dxz,yz orbitals interact with the N px,y orbitals, which contribute to the high transmission coefficient at the Fermi level for spin-down electrons. Meanwhile, the Co s-dz2 hybridization orbitals, which interact weakly with the N p orbitals, contribute to the small transmission coefficient at the Fermi level. This can also be verified by the molecular junction model adopting simple monatomic Co chain electrodes, which also show a perfect spin-filter effect and achieve an ideal magnetoresistance. In contrast, in the case of hexagonal Co electrodes, the spin-filter effect disappears. However, the effect appears again by adding one more Co atom to the central point contact. Our findings show that the spin-resolved electronic transport of molecular junctions depends on the stretching process and the nature of the electrodes, which can help in the future design of molecular devices based on the spin degree of freedom.

Magnetic and Thermospin Transport Properties of Triangular Graphene-Flake-Doped Boron Nitride Nanotubes

Magnetic nanotubes are a new material platform to realize the spin-dependent Seebeck effect (SDSE) and thermal spin-filtering effect (TSFE) in spin caloritronics. Here, we designed several magnetic nanotubes using triangular graphene-flake-doped boron nitride nanotubes (GFBNNTs) and found that the band structure of these GFBNNTs can be effectively engineered by embedding graphene flakes (GFs) of different sizes. The magnetic boron nitride nanotubes (BNNTs) ((5, 5)-6N) generate a good SDSE with nearly symmetric spin-up and spin-down currents, while the magnetic BNNTs ((10, 0)-6N) generate a good TSFE. These theoretical results about the SDSE and TSFE in nanotubes enrich the spin caloritronics and suggest material candidates to realize the SDSE and other inspiring thermospin phenomena.

Spin-dependent transport in a driven non-collinear antiferromagnetic fractal network

Non-collinear magnetic texture breaks the spin-sublattice symmetry which gives rise to a spin-splitting effect. Inspired by this, we study the spin-dependent transport properties in a non-collinear antiferromagnetic fractal structure, namely, the Sierpinski Gasket (SPG) triangle. We find that though the spin-up and spin-down currents are different, the degree of spin polarization is too weak. Finally, we come up with a proposal, where the degree of spin polarization can be enhanced significantly in the presence of a time-periodic driving field. Such a prescription of getting spin-filtering effect from an unpolarized source in a fractal network is completely new to the best of our knowledge. Starting from a higher generation of SPG to smaller ones, the precise dependencies of driving field parameters, spin-dependent scattering strength, interface sensitivity on spin polarization are critically investigated. The spatial distribution of spin-resolved bond current density is also explored. Interestingly, our proposed setup exhibits finite spin polarization for different spin-quantization axes. Arbitrarily polarized light is considered and its effect is incorporated through Floquet–Bloch ansatz. All the spin-resolved transport quantities are computed using Green’s function formalism following the Landauer–Büttiker prescription. In light of the experimental feasibility of such fractal structures and manipulation of magnetic textures, the present work brings forth new insights into spintronic properties of non-collinear antiferromagnetic SPG. This should also entice the AFM spintronic community to explore other fractal structures with the possibility of unconventional features.

Perfect spin-filtering effect in molecular junctions based on half-metallic penta-hexa-graphene nanoribbons

The design and control of spintronic devices is a research hotspot in the field of electronics, and pure carbon-based materials provide new opportunities for the construction of electronic devices with excellent performance. Using density functional theory in combination with nonequilibrium Green’s functions method, we design spin filter devices based on Penta-hexa-graphene (PHG) nanoribbons—a carbon nanomaterial in which the intrinsic magnetic moments combines with edge effects leading to a half-metallic property. Spin-resolved electronic transport studies show that such carbon-based devices can achieve nearly 100% spin filtering effect at low bias voltages. Such SEF can resist the influence of hydrogen passivation at different positions, but hardly survive under a hydrogen-rich environment. Our analysis show that the perfect SEF transport properties are caused by the magnetic and electronic properties of PHG nanoribbons, especially the magnetic moments on the quasi-sp 3 carbons. These interesting results indicate that PHG nanomaterials have very prominent application prospects in future spintronic devices.

Multifunctional Two-Dimensional VSi 2 N 4 / WSi 2 N 4 / VSi 2 N 4 Photodetector Driven by the Photogalvanic

Semiconducting monolayer $\mathrm{Mo}\mathrm{Si}$${}_{2}$$\mathrm{N}$${}_{4}$ and monolayer $\mathrm{WSi}$${}_{2}$$\mathrm{N}$${}_{4}$ have recently been fabricated and a number of two-dimensional (2D) materials with the same chemical formula and symmetry have been predicted, the mechanical, optical, and thermoelectric properties of which have been investigated. However, research regarding device applications of this 2D family have been very limited so far. Here, we propose a photodetector based on a 2D $\mathrm{VSi}$${}_{2}$$\mathrm{N}$${}_{4}$/$\mathrm{WSi}$${}_{2}$$\mathrm{N}$${}_{4}$/$\mathrm{VSi}$${}_{2}$$\mathrm{N}$${}_{4}$ lateral heterojunction, and investigate the transport properties of the photocurrent by using quantum transport simulations. The dependence of the photocurrent on the incident angle $\ensuremath{\alpha}$ and on the light-polarization angle $\ensuremath{\theta}$ is formulated. A robust photogalvanic effect is generated under the illumination of linearly polarized light due to the noncentrosymmetric ${C}_{2v}$ symmetry of the photodetector. The photocurrent has a $\mathrm{cos}(2\ensuremath{\theta})$ and $\mathrm{cos}(2\ensuremath{\alpha})$ dependence on the light polarization and on the incident angle, respectively. A pure spin current, a perfect spin-filtering effect, and an excellent spin-valve effect can be achieved at zero bias for a broad photon energy range with an appropriate polarization angle at both normal and horizontal incidence. Moreover, at horizontal incidence, the photocurrent is highly polarization sensitive with an extinction ratio of up to ${10}^{4}$. These results suggest that the 2D $\mathrm{WSi}$${}_{2}$$\mathrm{N}$${}_{4}$ family has promising multifunctional applications in low-power optoelectronics and spintronics.

Magnetothermoelectric properties of Al-Porphyrin sandwiched by graphene nanoribbon electrode based on quantum interference

Rational design of single-molecular junction for efficient thermoelectric properties is a key prerequisite for thermoelectric conversion and fundamental challenge because of the existence of restrictive relationship between Seebeck coefficient and conductance. Inspired by the promising mechanism for promoting thermoelectric properties depended on spin-filter efficiency, magnetothermoelectric properties of aluminum porphyrin (Al-porphyrin) molecular junction have been investigated in contact with ferromagnetic graphene electrodes at different temperature. It is found that spin-resolved Seebeck coefficient is larger than charge-resolved Seebeck coefficient, leading to an excellent spin-resolved power factor about 0.3 pW/K2 at 0.25 eV for Al-porphyrin molecular junction. Ferromagnetic leads effectively realize thermal spin-filtering effect (SFE), which is induced by spin-resolved quantum interference (SQI) between graphene electrode and central nonmagnetic Al-porphyrin molecule. These results indicate the prospects of Al-porphyrin molecular junction applications in spin-caloritronics.

Modulating spintronic properties of Nitrogen passivated borophene nanoribbons

We investigate the stability, magnetic, and transport features of pristine zigzag borophene nanoribbons (ZBNRs) and those edge-passivated by H and N atoms. The calculations were performed using non-equilibrium Green’s function and density functional theory approach. Our main focus is to study the transport properties of N-passivated ZBNRs. The results show that the stability of the nanoribbon increases by passivating the edges. The magnetic features of borophene nanoribbon are affected by the hanging bond of the edges. Hydrogenation can remove the magnetism on the edge, but the passivation by N atoms can increase the magnetic properties. It is revealed that the Nitrogenation causes the negative differential resistance (NDR) phenomenon and 65% spin filtering effect. The estimated Curie temperature for N atom passivated on both edges of ZBNR (NN-ZBNR) is higher than 6000 K, indicating that NN-ZBNR may be good room-temperature ferromagnetic material for spintronic applications in the future.

Tuning of the electronic structures and spin-dependent transport properties of phosphorene nanoribbons by vanadium substitutional doping

Based on vanadium-doped zigzag phosphorene nanoribbon (ZPNRs), we investigate the electronic structures and spin-dependent transport properties by the first-principles calculations in combination with the nonequilibrium Green's function approach. We find that the ZPNRs can be tuned from nonmagnetic metals to magnetic metals or half-metals by different doping positions, which are caused by the hybridization among different electron orbitals under the crystal field. Moreover, a robust negative differential resistance effect is observed in all studied devices, and a perfect spin-filter effect with almost 100% spin polarization can be found under low bias. We analyze the transport properties in detail from the viewpoint of the transmission spectrum and molecular energy levels. These results indicate that the vanadium-doped ZPNRs have potential applications as multi-functional spintronic devices. • Zigzag phosphorene nanoribbons can be tuned from nonmagnetic metals to magnetic metals or half-metals. • Robust negative differential resistance effect is observed. • Perfect spin-filter effect with almost 100% spin polarization can be found. • We analyze the transport properties in detail.

Electronic properties and spintronic applications of r-N-graphyne nanoribbons

Similar to pure graphyne, two-dimension carbon nitride graphyne also possesses exceptional properties and potential applications. In this work, by using the density functional theory (DFT) and combining with nonequilibrium Green’s function (NEGF), we study the electronic band structures and transport properties of zigzag rhombic N-graphyne nanoribbons (ZrNGYNRs). Our results show that all of the ZrNGYNRs have similar metallic band structures in no magnetic and ferromagnetic configuration, while the transport properties are directly related to the symmetry of the systems. The electron band structure exhibits a distinct spin splitting in the ferromagnetic state. We propose a device by cutting the ZrNGYNRs in the central scattering region. Negative differential resistance, rectification effects, and spin-filtering effects can be observed in this device. This work highlights the outstanding physics of ZrNGYNRs, and suggest that the ZrNGYNRs is a very promising material in the application of nanoelectronics . • First numerical simulation on the electronic property for zigzag-edge rhombic N-graphyne nanoribbons. • A proposed junction based on zigzag-edge rhombic N-graphyne nanoribbon symmetrically with good circuit performance. • The spin-filtering efficiency can be up to 100%, and the maximum of rectification ratio reaches up to 10 7 .

Combined spin filtering actions in hybrid magnetic junctions based on organic chains covalently attached to graphene.

We present a bias-controlled spin-filtering mechanism in spin-valves including a hybrid organic chain/graphene interface. Wet growth conditions of oligomeric molecular chains would usually lead, during standard CMOS-compatible fabrication processes, to the quenching of spintronics properties of metallic spin sources due to oxidation. We demonstrate by X-ray photoelectron spectroscopy that the use of a protective graphene layer fully preserves the metallic character of the ferromagnetic surface and thus its capability to deliver spin polarized currents. We focus here on a small aromatic chain of controllable lengths, formed by nitrobenzene monomers and derived from the commercial 4-nitrobenzene diazonium tetrafluoroborate, covalently attached to the graphene passivated spin sources thanks to electroreduction. A unique bias dependent switch of the spin signal is then observed in complete spin valve devices, from minority to majority spin carriers filtering. First-principles calculations are used to highlight the key role played by the spin-dependent hybridization of electronic states present at the different interfaces. Our work is a first step towards the exploration of spin transport using different functional molecular chains. It opens the perspective of atomic tailoring of magnetic junction devices towards spin and quantum transport control, thanks to the flexibility of ambient electrochemical surface functionalization processes.