Spin Filtering Effect Research Articles

Giant Tunneling Magnetoresistance in Spin-Filter Magnetic Tunnel Junctions Based on van der Waals A-Type Antiferromagnet CrSBr

Two-dimensional van der Waals magnetic materials have demonstrated great potential for new-generation high-performance and versatile spintronic devices. Among them, magnetic tunnel junctions (MTJs) based on A-type antiferromagnets, such as CrI3, possess record-high tunneling magnetoresistance (TMR) because of the spin filter effect of each insulating unit ferromagnetic layer. However, the relatively low working temperature and the instability of the chromium halides hinder applications of this system. Using a different technical scheme, we fabricated the MTJs based on an air-stable A-type antiferromagnet, CrSBr, and observed a giant TMR of up to 47000% at 5 K. Meanwhile, because of a relatively high Néel temperature of CrSBr, a sizable TMR of about 50% was observed at 130 K, which makes a big step towards spintronic devices at room temperature. Our results reveal the potential of realizing magnetic information storage in CrSBr-based spin-filter MTJs.

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.

Large magnetoresistance and temperature-driven spin filter effect in spin valve based on half Heusler alloy.

High spin-injection-efficiency (SIE) and thermal spin-filter-effect (SFE) from a magnetic material to a barrier material are crucial to the high performance of a spintronic device and a spin caloritronic device, respectively. By performing a nonequilibrium Green's function combined with first-principles calculations, we study the voltage-driven and temperature-driven spin transport properties of a half Heusler alloy RuCrAs based spin valve with different atom-terminated interfaces. The spin valve with a CrAs-top (or Ru-top) interface structure has an ultrahigh equilibrium magnetoresistance (MR) ratio of ∼1.56 × 109% (or ∼5.14 × 108%), ∼100% SIE, a large MR ratio, and high spin current intensity under bias voltage, suggesting that it has a great potential application in spintronic devices. The spin valve with the CrAs-top (or CrAs-bri) interface structure has a perfect SFE due to its very high spin polarization of temperature-driven currents, and it is useful in spin caloritronic devices.

High-performance spin-filtering and spin-rectifying effects in Blatter radical-based molecular spintronic device

We design a Blatter radical-based molecular spintronic device, and investigate its spin-polarized transport properties using density functional theory and non-equilibrium Green’s function technique. High-performance spin-rectifying and spin-filtering effects are realized. The physical mechanism is explained by the spin-resolved bias voltage-dependent transmission spectra, the energy levels of the corresponding molecular projected self-consistent Hamiltonian orbitals, and their spatial distributions. The results demonstrate that the Blatter radical has great potential in the development of high-performance multifunctional molecular spintronic devices.

Spin-dependent transmission in curved graphene superlattice

We investigate spin-dependent transmission in a curved graphene superlattice of N cells where each one is made up of four regions. The first is concave, and the third is convex, two arcs of circles separated by a distance d from flat graphene sheets. The tunneling analysis allows us to determine all transmission and reflection channels associated with our system. As a result, we show that the number of cells acts by decreasing the transmissions with the same spin. We predict a solid spin-filtering effect when d and N are sufficiently large. Finally, it is determined that the degree and duration of suppression of the transmissions with the same spin over a range of energy are controllable using d.

Generation of spin-polarized electronic currents using perpendicularly magnetized cobalt ferrite spin-filtering barriers grown on spinel-type-conductive layers

We demonstrated the generation of perpendicularly spin-polarized electronic currents using a tunnel spin-filtering effect through insulative Fe-rich cobalt ferrite CoxFe3−xO4+δ (I-CFO) barriers with perpendicular magnetic anisotropy (PMA). The I-CFO films grown on conductive Fe-rich cobalt ferrite CoyFe3−yO4 (C-CFO) films, which were deposited on additional I-CFO buffer layers on MgO(001) substrates, exhibited PMA induced by an epitaxial strain. Magnetic tunnel junctions (MTJs), which comprise C-CFO electrode layers, I-CFO barrier layers, and perpendicularly magnetized Co/{Tb/Co}15/Co spin detection layers, showed a tunnel magnetoresistance (TMR) effect. This indicated that spin-polarized tunnel currents were injected into the spin detection layers. A spin injection efficiency of −28% was observed for the MTJs with an I-CFO barrier of 3.0 nm in thickness at 100 K. The voltage dependence of the TMR effect indicates that the spin-injection efficiency is affected by voltage-dependent changes in the effective spin-dependent barrier width. The combination of spinel-type C-CFO and I-CFO films with well-controlled compositions and lattice strains is, therefore, applicable as a spin-injection source for spintronics devices when perpendicularly spin-polarized electronic currents are required.

Flat-band states induced negative differential resistance in organic-ferromagnetic devices

Spin-dependent transport via flat-band states in organic-ferromagnetic devices with spin radicals is investigated theoretically. A spin-resolved negative differential resistance phenomenon is observed together with a spin-filtering effect. A new mechanism as bias-induced distinct localization of the spin-split flat-band states is proposed, which originates from the weaker hybridization of the flat-band states rather than the π-conjugated orbitals. The peak-to-valley ratio increases with the interaction strength between the main chain and radicals. This work explores the unique transport property of flat-band states and their intriguing prospect in designing high-performed organic spintronic devices.

Ultrasound-Directed Symmetry Breaking and Spin Filtering of Supramolecular Assemblies from only Achiral Building Blocks.

Herein we describe the self-assembly of an achiral molecule into macroscopic helicity as well as the emergent chiral-selective spin-filtering effect. It was found that a benzene-1,3,5-tricarboxamide (BTA) motif with an aminopyridine group in each arm could coordinate with AgI and self-assemble into nanospheres. Upon sonication, symmetry breaking occurred and the nanospheres transferred into helical nanofibers with strong CD signals. Although the sign of the CD signals appeared randomly, it could be controlled by using the as-made chiral assemblies as a seed. Furthermore, it was found that the charge transport of the helical nanofibers was highly selective with a spin-polarization transport of up to 45 %, although the chiral nanofibers are composed exclusively from achiral building blocks. This work demonstrates symmetry breaking under sonication and the chiral-selective spin-filtering effect.

Spin-transport across a two-dimensional metal-semiconductor interface with infinite potential in presence of spin-orbit interactions: Double refraction and spin-filtering effect

The spin-transport across a two-dimensional metal-semiconductor junction with a Dirac-delta function potential at the interface and the Rashba and Dresselhaus spin-orbit interactions in the semiconductor region is studied exactly using discontinuous boundary conditions and the spin-polarized reflected and refracted current density and differential conductance are calculated. It is shown that in the presence of an infinite interface potential, an increase in the incident electron's energy reduces the spin splitting. It is also shown that the reflected and refracted coefficients, the spin-polarized currents and the corresponding differential conductance depend strongly on the spin-orbit interactions. The reflected spin polarization, however, becomes zero due to the infinite potential. The Rashba coupling enhances the refracted spin polarization while the Dresselhaus coupling reduces it. Thus, the maximum in polarization occurs at small values of Dresselhaus coupling and large values Rashba coupling. Interestingly, though the presence of delta-potential at the interface does not change the splitting angle between the spin-up and spin-down electrons, it causes a constant shift in the spin polarization.

Interface design for the transport properties in asymmetric two-dimensional van der Waals multiferroic tunnel junctions

Multiferroic tunnel junctions (MFTJs) composed of ferroelectricity and ferromagnetism have attractive prospects in memory and computing device applications due to their low power consumption and nonvolatile switching. However, achieving both spin filter effect (SFE) and excellent tunnel electroresistance (TER) effect in two-dimensional (2D) van der Waals (vdW) MFTJs still remain challenging. Herein, using first-principles calculations, we investigate interface design for electronic and transport properties of asymmetric 2D vdW MFTJs that consist of CrI 3 , graphene, and ferroelectric Sc 2 CO 2 (containing Sc– P↑ and Sc– P↓ states). We find that such CrI 3/Sc– P↑/graphene MFTJs exhibit p -type Ohmic contact for Sc– P↑/graphene and SFE for CrI 3 / Sc– P↑ due to the transformation of CrI 3 from intrinsic semiconductor to half-metal. Simultaneously, the Dirac point of graphene at the Fermi energy has a big shift about 0.95 eV with the polarization reversal, suggesting that there is a giant barrier modulation. Moreover, the huge TER ratio about 1.7′10 5 % was also discovered by transport calculations. Our results provide an avenue for the design of future 2D vdW MFTJs. • 2D CrI 3 /Sc 2 CO 2 /graphene van der Waals MFTJ shows multiple nonvolatile resistance and high ratio of tunneling electroresistance. • Two heterointerfaces in CrI 3 / Sc– P↑/graphene exhibit Ohmic contact, while those in CrI 3 / Sc– P↓/graphene are Schottky contact. • Spin filter effect can take place in CrI 3 / Sc– P↑/graphene due to the transformation of CrI 3 from intrinsic semiconductor to half-metal. • Dirac point of graphene at the Fermi energy has a big shift about 0.95 eV with the polarization reversal.

Spin-switching effect and giant magnetoresistance in quantum structure of monolayer MoS<sub>2</sub> nanoribbons with ferromagnetic electrode

Spintronics is a new type of electronics based on electron spin rather than charge as the information carrier, which can be stored and calculated by regulating and manipulating the spin. The discovery and application of the giant magnetoresistance effect opens the door to the application of electron spin properties. Realizing on-demand control of spin degree of freedom for spin-based devices is essential. The two-dimensional novel material, monolayer transition metal dichalcogenide (TMD) (MoS<sub>2</sub> is a typical example from the family of TMD materials), has become an excellent platform for studying spintronics due to its novel physical properties, such as direct band gap and strong spin-orbit coupling. Obtaining high spin polarization and achieving controllability of degrees of freedom are fundamental problems in spintronics. In this paper, we construct the monolayer zigzag MoS<sub>2</sub> nanoribbon quantum structure of electrically controlled ferromagnetic electrode to solve this problem. Based on the non-equilibrium Green’s function method, the regulation of the magnetic exchange field and electrostatic barrier on the spin transport in parallel configuration and anti-parallel configuration are studied. It is found that in the parallel structure, spin transport is obviously related to the magnetic exchange field, and 100% spin filtering can occur near the Fermi energy level to obtain pure spin current. When an additional electric field is applied to the middle region, the spin filtering effect is more significant. Therefore, the spin switching effect can be achieved by regulating the incident energy. In addition, it is also found that within a specific energy range, electrons in the parallel configuration are excited to participate in transport, while electrons in the anti-parallel structure are significantly inhibited. Consequently, a noticeable giant magnetoresistance effect can be obtained in this quantum structure. Moreover, it can be seen that the magnetic exchange field strength can effectively modulate the giant magnetoresistance effect. These results provide valuable theoretical references for the development of giant magnetoresistance devices and spin filters based on monolayer zigzag MoS<sub>2</sub> nanoribbons.

Interface engineering strategy for multisource spintronic devices via TMPS4 modulation of black-phosphorus.

Interface engineering is an effective strategy for significantly providing performance improvements in logic operations and information storage techniques, given the quantum effects characteristic of pristine two-dimensional ferromagnetic (FM) materials. Furthermore, the van der Waals (vdW) heterostructures enable a more efficient design of logic components. Herein, two novel designs of van der Waals heterostructures are proposed, black-phosphorus (BP)/TMPS4(TM = Cr, Fe-Mn), where the CrPS4 relies on odd and even layers for FM state - antiferromagnetic (AFM) state alternation, which is used to modulate BP with high hole mobility but no magnetism. Based on the first principles, the simulation results show that the two heterojunctions exhibit high stability, carrier mobility, and thermoelectric effects, of which the BP/CrPS4 heterojunction is specifically modulated to a type II electronic bandstructure. These two structures are applied in multi-source logic devices. The device performances show that the devices have spin Sebeck effect (SSE), perfect spin filtering effect (SFE), high extinction ratio (1347), and high thermal magnetoresistivity (1011). The above results suggest BP/TMPS4 bilayers as promising candidates for spin-based vdW devices and facilitate the future development of atomically thin magnetic information storage.

Ferromagnetic half-metal with high Curie temperature in Cr P nanoribbons: good material for spintronic applications.

In this work, the stability, and electronic, magnetic, and transport characteristics of chromium phosphorus nanoribbons (CrPNRs) have been investigated. The results, obtained from the non-equilibrium Green's function and density functional theory, indicate that the nanoribbon is stable in terms of binding energies as well as dynamically. The calculated electronic structure shows that this nanoribbon has an indirect band gap of about 1.67 eV for the spin-down channel and is metallic for the spin-up channel. The metallicity of the spin-up channel originates from the P-3p orbitals and the magnetic properties are due to the Cr-3d orbitals. The obtained transport properties indicate the value of the current for the spin-up state is about 50 μA. The negative differential resistance (NDR) phenomenon and also a 100% spin filtering effect are seen between voltages of 0.4 and 0.5 V. The results showed that CrPNRs have a high Curie temperature of more than 690 K, indicating that this nanoribbon is a useful ferromagnetic material for nanoelectronic devices and spintronic applications at ambient temperature.

Bipolar spin-filtering and giant magnetoresistance effect in spin-semiconducting zigzag graphene nanoribbons.

Spintronics is one of the main topics in condensed matter physics, in which half-metallicity and giant magnetoresistance are two important objects to achieve. In this work, we study the spin dependent transport properties of zigzag graphene nanoribbons (ZGNR) with asymmetric edge hydrogenation and different magnetic configurations using the non-equilibrium Green's function method combined with density functional calculations. Our results show that when the magnetic configurations of the electrodes change from parallel to antiparallel, the currents in the tunnel junction change substantially, resulting in a high conductance state and a low conductance state, with the tunnel magnetoresistance (TMR) ratio larger than 1 × 105% achieved. In addition, in the parallel magnetic configurations, an ideal bipolar spin filtering effect is observed, making it flexible to switch the spin polarity of current by reversing the bias direction. All these features originate from the spin semiconducting behavior of the asymmetrically hydrogenated ZGNRs. The findings suggest that asymmetric edge hydrogenation provides an important way to construct multi-functional spintronic devices with ZGNRs.

Spin-gapless van der Waals heterostructure for spin gating through magnetic injection devices.

Spin-gapless semiconductors (SGSs) are new magnetic zero-bandgap materials whose band structure is extremely sensitive to external influences (pressure or magnetic fields) and have great potential for high-speed and low-energy spintronics applications. The first-principles method was used to systematically study the heterostructures constructed of an asymmetric surface-functionalized Janus MXene material, Cr2NOF, and a two-dimensional hexagonal lattice (2DH) semiconductor material and to study the effects of the electronic structure, Curie temperature, magnetism, and the design of unusual band structures and magnetic injection in the bilayer to obtain an SGS structure. Through the design and construction of Cr2NOF/2DH van der Waals heterojunction spintronic devices, the spin-filtering effect of the devices can reach 100%, especially, realizing spin gating through magnetic injection. We report the transport mechanism of the heterojunction spintronic devices to achieve the goal of a controllable optimization of the device functions, which provides a theoretical basis for the design of MXene van der Waals heterojunctions for high-efficiency and low-power-consumption spintronic devices.

Spin-dependent transport properties of a tetra-coordinated Fe(II) spin-crossover complex

Spin-crossover (SCO) complexes are being regarded as one of the most promising components of molecular spintronics, since they can exhibit different spin states (high-spin/HS or low-spin/LS) in response to external stimuli. Here, the electronic structure as well as the transport properties of a tetra-coordinated bis(formazanate) Fe(II) SCO complex have been investigated with the DFT + NEGF approach. From the calculated results, the transition between different spin states of the Fe(II) SCO complex is accompanied by a variation of the Fe-N bond length and the dihedral angle between the planes of the ligands. The I-V curves of the molecular junctions revealed that the SCO complexes in different spin configurations display significantly different bias-dependent characteristics. When the bias is above 0.1 V, the current through the HS-configured molecular junction increases rapidly and is significantly greater as compared to that in the LS configuration. Furthermore, the transport properties of the HS-state SCO complex are dominated by spin-up electrons, indicating a strong spin-filtering effect.

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.

Controllable Spin Filtering by δ-Doping for Electrons in Magnetically and Electrically Modulated Semiconductor Nanostructure

In this paper, we theoretically investigate how to control spin filtering via a [Formula: see text]-doping for electrons in a magnetically and electrically modulated semiconductor nanostructure (MEMSN), which can be realized by patterning a ferromagnetic (FM) stripe and a Schottky-metal (SM) stripe on top and bottom of GaAs/AlxGa[Formula: see text]As heterostructure in experiments, respectively. A considerable spin filtering effect still exists because of spin–orbit coupling (SOC), even if a [Formula: see text]-doping is included. Moreover, spin polarization ratio can be manipulated by [Formula: see text]-doping, which may lead to a structurally-controllable electron-spin filter for semiconductor spintronics.

Excellent spin-filtering and giant tunneling magnetoresistance in a dual-electrode van der Waals magnetic tunnel junction based on ferromagnetic CrSe2

Magnetic tunnel junctions (MTJs) both with efficient spin-filtering effect and large tunneling magnetoresistance (TMR) ratio are extremely attractive and highly desirable in the field of spintronics. Inspired by recent successful preparation of a stable two-dimensional (2D) layered ferromagnet 1T-CrSe2 on a 2H-WSe2 substrate via chemical vapor deposition (CVD) synthesis, herein, employing first-principles calculations, we investigate the spin-dependent transport properties of van der Waals (vdW) MTJs built with a monolayer 2H-WSe2 tunnel barrier and a 1T-CrSe2 single-electrode or a 1T-MoSe2/1T-CrSe2 dual-electrode. Compared to low TMR (67.3%) in single-electrode MTJ, dual-electrode MTJ exhibits excellent spin-filtering effect (with 99.96% spin polarization) and a giant TMR ratio (up to 2.29 × 105%), which mainly originates from the half-metallicity of CrSe2 induced by charge transfer at MoSe2/CrSe2 interface. Relatively high TMR values (over 1 × 103%) are always maintained at small bias voltages (|Vb| ≤ 0.35 V). Our work have for the first time theoretically verified feasibility of realizing the transition of 2D CrSe2 from metallicity to half-metallicity in the vdW MTJ and yielding excellent spin-filtering and giant magnetoresistance via electrode interface engineering, thereby providing important theoretical guidance for the experimental design of high-performance vdW MTJs in spintronic devices.

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.