Perfect Spin Filtering Research Articles

Magnetic tunnel junction based on bilayer LaI2 as perfect spin filter device

The discovery of van der Waals intrinsic magnets has expanded the possibilities of realizing spintronics devices. We investigate the transmission, tunneling magnetoresistance ratio, and spin injection efficiency of bilayer LaI2 using a combination of first-principles calculations and the non-equilibrium Green’s function method. Multilayer graphene electrodes are employed to build a magnetic tunnel junction with bilayer LaI2 as ferromagnetic barrier. The magnetic tunnel junction turns out to be a perfect spin filter device with an outstanding tunneling magnetoresistance ratio of 653% under a bias of 0.1 V and a still excellent performance in a wide bias range. In combination with the obtained high spin injection efficiency this opens up great potential from the application point of view.

Perfect Spin Filtering, Giant Magnetoresistance, and Rectification Behavior Induced by V‐Doped Zigzag Graphene Nanoribbons

AbstractEmploying the constructs of density functional theory (DFT) and the Nonequilibrium Green's Function (NEGF), the investigation extensively explores the electronic and transport properties of zigzag graphene nanoribbons (ZGNRs) doped with vanadium (V). Notably, this inquiry unveils that strategic doping can transform V‐doped ZGNRs into spintronic nanodevices with distinctive transport attributes. Initially, the simulations showcase remarkably high spin‐filtering efficiencies (SFEs) at certain bias voltages. Furthermore, a giant magnetoresistance (GMR) peaking at 6.87 10 is detected. In conclusion, the examination discerns a spin rectifier that exhibits a significant rectification ratio (RR) of 9.62 10. This research delineates a viable trajectory for the refinement of high‐performance spintronics in ZGNRs via vanadium doping. The implications of this study indicate that the model harbors considerable promise for application in miniature spintronic devices.

Spin-polarized electrical transport properties of organic radicals in presence of zigzag-graphene nanoribbon leads.

The present work delves into the spin-polarized transport property of organic radicals sandwiched between two zigzag-graphene nanoribbon (ZGNR) electrodes by employing density functional theory and nonequilibrium Green's function technique. We demonstrated that the magnetic center(s) of the radical can manipulate the localized edge states of the ZGNR in the scattering region, causing ferromagnetic coupling. Such manipulation of the magnetic edges results in a high spin-filter effect in molecular junctions, and even the antiferromagnetic diradicals serve as nearly perfect spin filters. We have confirmed that this is a general phenomenon of ZGNR by analyzing two antiferromagnetic diradicals and a doublet. The spin-polarized density of states, transmission spectra, and current vs voltage curves of the systems provide strong evidence for our findings. This research strongly suggests that ZGNRs attached with organic radicals could be the perfect building blocks for spintronic materials.

Symmetry-driven half-integer conductance quantization in Cobalt–fulvalene sandwich nanowire

Precise manipulation and monitoring spin transport in one-dimensional (1D) systems is a long-sought goal in the field of nano-spintronics. Based on first-principles calculations, we report the observation of half-integer conductance quantization in the Cobalt-fulvalene sandwich nanowire. Compared with a pure monatomic Cobalt wire, the introduction of fulvalene molecules leads to three important features: Firstly, the strong coupling between the fulvalene and the Cobalt prevents the contamination of the ambient air, ensuring both chemical and physical stabilities; Secondly, the fulvalene symmetry-selectively filters out most of the d-type orbitals of the Cobalt while leaving a single d-type orbital to form an open spin channel around the Fermi level, which offers a mechanism to achieve the observed half-integer conductance; Thirdly, it maintains a superexchange coupling between adjacent Co atoms to achieve a high Curie temperature. Spin transport calculations show that this half-metallic nanowire can serve as a perfect spin filter or a spin valve device, thus revealing the potential of Cobalt-fulvalene sandwich nanowire as a promising building block of high-performance spintronics technology.

Strain-controlled spin transport in a two-dimensional (2D) nanomagnet

Semiconductors with controllable electronic transport coupled with magnetic behaviour, offering programmable spin arrangements present enticing potential for next generation intelligent technologies. Integrating and linking these two properties has been a long standing challenge for material researchers. Recent discoveries in two-dimensional (2D) magnet shows an ability to tune and control the electronic and magnetic phases at ambient temperature. Here, we illustrate controlled spin transport within the magnetic phase of the 2D semiconductor CrOBr and reveal a substantial connection between its magnetic order and charge carriers. First, we systematically analyse the strain-induced electronic behaviour of 2D CrOBr using density functional theory calculations. Our study demonstrates the phase transition from a magnetic semiconductor → half metal → magnetic metal in the material under strain application, creating intriguing spin-resolved conductance with 100% spin polarisation and spin-injection efficiency. Additionally, the spin-polarised current–voltage (I–V) trend displayed conductance variations with high strain-assisted tunability and a peak-to-valley ratio as well as switching efficiency. Our study reveals that CrOBr can exhibit highly anisotropic behaviour with perfect spin filtering, offering new implications for strain engineered magneto-electronic devices.

Ab Initio Investigations of Gallium Nitride Nanoribbons for Spin Filter and Negative Differential Behavior

This work demonstrates the influence of alternative edge passivation via H/F on the electronic and magnetic characteristics of gallium nitride nanoribbons (GaNNRs). For this study, the first-principles density functional theory (DFT) and non-equilibrium green function (NEGF) frameworks are deployed. Our study demonstrates that the selective edge passivation with F/H zigzag GaN nanoribbon (NR) is a strong contender for spintronics due to its half-metallic property under specific conditions. Various nano-configurations for the H/F ZGaNNRs passivation are investigated here. Thermodynamically, most stable configuration is alternate fluorinated F-GaN-F NR. Further, the negative differential resistance (NDR) behavior is also reported along with the perfect spin-filtering properties. This study paves the way to employ these 2-D nanostructures-based devices for spin filters, spin logic switches, and steep switching nanoelectronic devices.

DMRG analysis of magnetic order in the zigzag edges of hexagonal CrN nanoribbons

We investigate the finite-temperature magnetic order at the edges of hexagonal CrN nanoribbons by using density functional theory combined with the density matrix renormalization group (DMRG) method. Moreover, the spin-dependent transport in nanoribbons is calculated within the semiclassical Boltzmann transport theory. We find that the zigzag edges have lower energy with respect to armchair edges. The zigzag edges of CrN nanoribbon show half-metallic electronic character, which is the same as for the two-dimensional (2D) monolayer. The localized electronic states on the zigzag edges reduce the electronic band gap energy for spin-down electrons. The ab initio electronic results are mapped into an effective 1D Heisenberg spin model up to the next-nearest-neighbor exchange interaction term. For zigzag ribbons, the nearest-neighbor and next-nearest-neighbor magnetic exchange are around 10--12 and $\ensuremath{-}2$ to 0 $\text{meV}/\text{Cr}\phantom{\rule{4.pt}{0ex}}\text{atom}$, respectively. The finite spin correlation length in 1D nanoribbons drops sharply to zero with temperature. The absence of long-range spin correlations at the edges is a practical drawback for future room temperature 2D spintronic devices. The maximally localized Wannier functions are used for band interpolation and spin-dependent transport calculations by using the semiclassical Boltzmann equation. We show that the zigzag edges of CrN are a perfect spin filter under both electron and hole doping.

Designed Graphane-based spin filters by tuning the sp2/sp3 configuration

The electronic transport properties of H-vacancy-defected graphane are investigated by using the density functional theory (DFT) and Non-equilibrium Green’s Function (NEGF) methods. Results show that the band gap of graphane depends on the relative positions of the defect bands introduced by H vacancies and the valence or conduction bands, suggesting the band gap controllability. The defect bands are obviously spin polarized and the ratio is almost 100%. And the magnetization of the system can be tuned by defect concentration and location. Moreover, in the two-probe systems, the presence of H-vacancy-defect bands near the Ef plays an important role in controlling spin-dependent transport of graphane. A perfect spin-filtering effect with 100% spin polarization could be realized by H-vacancy defects. The spin properties indicate the potential of graphane as an option for future graphene-based spin filters and spintronic devices.

Nearly perfect spin-filtering effect with tunable spin-polarization direction and huge magnetoresistance in molecular spin valves

Spin-transport properties of molecular spin valves constructed by two chromium-salophene (CrSal) molecules connected with boron nitride (BN) atomic chains are investigated by applying a nonequiblium Green's function method with density functional theory. Nearly perfect spin-filtering effect can be found when the molecular spin valves are set in parallel magnetic configuration. In particular, the direction of the detected spin-polarization signal is reversible by tuning the types of BN atomic chains. Moreover, obvious magnetoresistance (MR) effects are also found in the molecular spin valves. More importantly, the MR ratio can be changed from about 359% to about 1.31×105% by adjusting the types of BN atomic chains. Our work provides a new avenue to realize high-performance multifunctional molecular spin valves.

High anisotropic magnetoresistance, perfect spin-filtering effect, and negative differential resistance effect of Cr-doped anatase phase TiO2

Anisotropy-based half-metallic materials are highly efficient in spintronic devices and have important applications in spintronics. Anatase phase TiO2 has attracted much attention because of its anisotropy, but its non-magnetism limits its applications in spintronics. We investigate the electronic structure of 3d transition metal-doped anatase phase TiO2 by first principles method to achieve spin injection of anatase. The calculation results exhibit that the Sc, Cr, Mn, Fe, and Ni-doped systems are half-metallic ferromagnets while other doped systems behave as magnetic metals except the V-doped system is a magnetic semiconductor. The calculated formation energy under O-rich condition are negative shows that all half-metals are thermodynamically stable, and we construct devices along the y-direction of the half-metal and find that the device based on the Cr-doped system has the best electronic transfer capacity under zero bias. Then we use the Cr-doped system as the electrode and the pure anatase unit cell as the central scattering region to construct devices in different directions. We find that the magnitude of the current along different transport directions varied greatly, and the calculated anisotropic magnetoresistance was as high as 300%. Furthermore, whether spin configurations (PC) or antiparallel configurations (APC), there is a 100% spin-filtering efficiency of the device, and we find a significant negative differential resistance effect of the device in PC. These results suggest that Cr-doped anatase phase TiO2 can be used in spintronics.

Multifunctional 2D g-C4N3/MoS2 vdW Heterostructure-Based Nanodevices: Spin Filtering and Gas Sensing Properties.

Two-dimensional (2D) magnetic materials are the key to the development of the new generation in spintronics technology and engineering multifunctional devices. Herein, the electronic, spin-resolved transmission, and gas sensing properties of the 2D g-C4N3/MoS2 van der Waals (vdW) heterostructure have been investigated by using density functional theory with non-equilibrium Green's function method. First, the g-C4N3/MoS2 vdW heterostructure demonstrates ferromagnetic half-metallicity and superior adsorption capacity for gas molecules. The spin-dependent electronic transport of the g-C4N3/MoS2-based nanodevice is obviously regulated by parallel or anti-parallel spin configuration in electrodes, leading to perfect single-spin conduction behavior with a nearly 100% spin filtering efficiency, a negative differential resistance effect, and other interesting electrical transport phenomena. Moreover, g-C4N3/MoS2 exhibits directional dependency and strong transport anisotropic behavior under bias windows, indicating that the electric current propagates more easily through the vertical direction than the horizontal direction. The physical mechanisms are revealed and analyzed by presenting the bias-dependent transmission spectra in combination with the projected local device density of states. Finally, the g-C4N3/MoS2-based gas sensor is more sensitive to CO, NO, NO2, and NH3 molecules with the chemisorption type. The strong chemical adsorption leads to the formation of electrons on the local scattering center and ultimately affects the transport properties, resulting in the maximum gas sensitivity reaching 6.45 for NO at the bias of 0.8 V. This work not only reveals that the g-C4N3/MoS2 vdW heterostructure with high anisotropy, perfect spin filtering, and outstanding gas sensitivity is a promising 2D material but also provides an insight into the further application in futuristic electronic nanodevices.

Half-metallicity and perfect spin-filtering effect based on vacancy interference in boron-phosphide nanoribbon: A first-principle study

Edge states and vacancy-induced defect states simultaneously occur near Fermi level of boron-phosphide nanoribbon (BPNR) when there is a vacancy in it, which is a compromise of two important influencing factors for electronic property modulation. Based on density functional theory, the effects of mono-vacancy on electronic structure of zigzag/armchair BPNRs have been investigated. Calculation results indicate that effects of the vacancy on electronic property of the system is mainly depended on edge configuration of the ribbon. Half-metallicity can be realized in zigzag BPNR with phosphorus vacancy. Furthermore, it is found that charge injection and transverse electric field can raise spin-polarization of zigzag BPNR with boron vacancy near rich-B edge. Most interestingly, it exhibits perfect bipolar spin filtering effect for the case of zigzag BPNR with a boron vacancy near rich-P edge.

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.

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.

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.

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.

Magnetism and perfect spin filtering in pristine MgCl2 nanoribbons modulated by edge modification.

The search for new materials, with ideal electronic and magnetic properties for potential applications in nanoelectronics, has been extremely successful so far, and has paved the way for us to reimagine all technological devices. In the present work, we study the design of MgCl2 nanoribbons for applications in nanoelectronics and spintronics, by employing first-principles calculations based on density functional theory (DFT) and non-equilibrium Greens function techniques. Our results show that the properties of MgCl2 nanoribbons depend strongly not only on their geometrical form (armchair or zigzag) but also on the atoms at their edges. The armchair MgCl2 nanoribbon is a semiconductor and the zigzag nanoribbons vary from semiconducting, to metallic, to ferromagnetic, and to half-metallic, depending on the edge terminations. All these nanoribbons are very stable, with a relatively low cohesive energy per atom, and their attributes are not affected by the width of the nanoribbon. From transport calculations, we observed partial spin filtering in the ferromagnetic nanoribbon and perfect spin filtering in the two half-metallic nanoribbons. Moreover, we show how the current versus voltage curves can be fully understood by analysing the alignment of the energy levels of the electrodes. Our results corroborate the promising use of single-layer MgCl2 for the development of spintronics devices.

Perfect spin Seebeck effect, spin-valve, spin-filter and spin-rectification based on the heterojunction of sawtooth graphene and graphyne nanoribbons.

In order to develop low-power-consumption electronic devices, we studied a heterojunction composed of a 5,4-sawtooth graphene nanoribbon and 6,6,12-graphyne nanoribbon by using first-principles calculations combined with the non-equilibrium Green's function approach. Some spin caloritronic and spintronic devices can be realized based on the heterojunction, exhibiting excellent and multifunctional properties: a net spin current and perfect spin Seebeck effect are generated, a thermal induced and bias induced colossal magnetoresistance is obtained, and a spin filter with 100% spin polarization and a spin rectification with a high rectification ratio are acquired. Our results indicate that the proposed heterojunction is a promising candidate for multi-effect and low-power-consumption electronic devices.

Zn-Passivated Zigzag Boron Nitride Nanoribbons for Perfect Spin-Filtering and Negative Differential Resistance Based Devices

The spin polarized structural, electronic, and transport properties of Zn-passivated zigzag boron nitride nanoribbons (ZBNNRs) at the selective boron and nitrogen edge atoms along with H-passivation are investigated. Present density functional theory (DFT) based studies predict that half-metallic property can be obtained in ZBNNRs via selective Zn and H-passivation. The spin active most stable structure of Zn-passivated ZBNNRs is H-BN-Zn irrespective of ribbon width. The current-voltage characteristics of the Zn-passivated ZBNNRs device exhibit the perfect spin-filter characteristics with magnificently high spin-filtering efficiency even under a low bias. Interestingly, the negative differential resistance (NDR) with a large <inline-formula><tex-math notation="LaTeX">$I_{P}/I_{V}$</tex-math></inline-formula> (peak-to-valley current ratio (PVCR)) of the order of <inline-formula><tex-math notation="LaTeX">$10^{3}$</tex-math></inline-formula> has also been observed for Zn-BN-H due to spin-up current component. This is because the dangling bonds at the edge atoms break the edge states and stimulates multiple local states, which prevents electron transfer and reduces current to get a better <inline-formula><tex-math notation="LaTeX">$I_{P}/I_{V}$</tex-math></inline-formula> ratio. The observed perfect spin-filtering characteristics and NDR effect suggest that Zn-passivated ZBNNRs have immense potentials to be deployed for nanoscale spintronic devices.