High Spin Filtering Efficiency Research Articles

Ultrahigh spin filter efficiency and large spin Seebeck polarization of binuclear manganese phthalocyanine molecular junctions on nickel electrodes

In this paper, we investigated the spin transport properties of binuclear manganese phthalocyanine (Mn2Pc2) spintronic devices sandwiched between two nickel electrodes using the non-equilibrium Green's function method in combination with density functional theory. Based on the calculation results, the Mn2Pc2 device exhibited excellent spin-filtering capabilities, demonstrating an exceptionally high spin filter efficiency (SFE). Irrespective of the parallel or antiparallel orientation of magnetization in the electrodes, we observed that when both manganese atoms were in a spin-up state, the SFE of spin-resolved currents under finite bias and the thermoelectric currents induced by temperature gradients at fixed temperatures were both close to 100%. The large spin Seebeck polarization of the Mn2Pc2 device was also obtained at low reference temperatures. This study explores the potential for developing multifunctional spintronic single-molecule devices using Ni−Mn2Pc2.

Demonstration of giant anisotropic magnetoresistance, high spin filtering efficiency, and negative differential resistance in nanodevices based on oxygen doped black arsenic phosphorus nanoribbons

We investigate the electrical properties of pure black arsenic phosphorus and oxygen atom doped monolayer black arsenic phosphorus using first principle calculations. The density of states results reveals that oxygen atom doped black arsenic phosphorus is a magnetic semiconductor. The current-voltage characteristic curves of oxygen atom doped monolayer black arsenic phosphorus nanoribbons based devices have been determined using the non-equilibrium Green's function associated with the density function theory. The results demonstrate that the device made of doped black arsenic phosphorus has a substantial current difference between armchair and zigzag black arsenic phosphorus nanoribbons, implying that the device made of nanoribbons has a large anisotropic magnetoresistance. The spin filtering efficiency is nearly 100% at some bias voltage levels, and the transmission spectrums of the associated bias voltage window can explain the significant negative differential resistance. Furthermore, these findings suggest that oxygen atom doped black arsenic-phosphorus nanoribbons are suitable for spintronic devices.

The effect of different dopants and their positions on the magnetic properties of an armchair antimonene nanoribbon: comprehensive theoretical investigation

In this work, using density functional theory, we have studied the magnetic properties of an armchair antimonone nanoribbon doped with transition metal (TM) atoms (Mn, Fe, Co, Ni, V, Cr) in various positions and different number of impurity atoms. The results show that the investigated magnetic properties, such as spin band gap, spin polarization and magnetic moment vary with type and distance from the edge of the ribbon and the number of impurities. The obtained values of magnetic moment reveal, Mn-doped nanoribbons have greater magnetization than Fe, Cr, V, Ni and Co doped ones. Also, spin polarization with significant values is observed in Mn and Fe doped structures. Our calculated spin currents demonstrate that introducing of TM dopants leads to efficient separation of spin up and down currents. Interestingly, nanoribbons with Mn, Cr and V dopants show high spin filter efficiency in a wide range of voltages. Thus, it seems that our results prepare a promising way to nanoscale spintronic 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.

Giant Magnetoresistance and Rectification Behavior in Fluorinated Zigzag Boron Nitride Nanoribbon for Spintronic Nanodevices

In the present work, the spin-polarized structural and electronic properties of fluorine (F) passivated zigzag boron nitride nanoribbons (ZBNNRs) at the selective boron (B) and nitrogen (N) edge atoms are investigated. This study is based on the density functional theory (DFT) along with non-equilibrium Green function (NEGF) formalism. Our study predicts that half-metallic property can be obtained in ZBNNRs via F passivation at selective edges. The F-passivated ZBNNRs are found to be structurally stable in both non-magnetic as well as magnetic ground states irrespective of their width. Hence, the transport properties of F-passivated ZBNNRs are also studied as fluorinated structures are reported to be more stable. The current-voltage characteristic of F-passivated ZBNNRs based devices exhibit the perfect spin-filter characteristics with magnificently high spin-filtering efficiency (SFE) even under a low bias. It is worth mentioning here that giant magnetoresistance resistance (GMR), and rectification ratio of the order of 10⁸and 10⁵ have also been observed for F-BN-F devices. This is because dangling bonds break the edge states' symmetry and induce some localized states, which suppress the electron transmission and reduce the current. The observed perfect spin-filtering characteristics, GMR, and rectifying characteristics suggest that Fpassivated ZBNNRs have immense potentials to be deployed for nanoscale spintronic devices.

Design of a Giant Magnetoresistance Device with High Spin Filter Efficiency

Molecular spintronics may boost the development of nanoscale devices with improved performance and enhanced functionality, which is very promising for the next generation of electronic devices. Here, we design a new type of spintronics device based on the novel 2D material C3N. Using nonequilibrium Green’s function in combination with the density functional theory, we systematically study the spin-dependent transport properties in four different magnetic configurations of the C3N junction, and the perfect spin filter efficiency and giant magnetoresistance effects are achieved. The calculated results clearly demonstrate that the transport properties of the C3N junction are sensitive to the magnetic configuration of the electrodes. The calculated spin-resolved transmission spectra of the proposed ferromagnetic coupling C3N junctions exhibit a robust spin filtering effect, where the conductance is mainly governed by the spin-down electrons. Under the small bias voltage, the transport properties are mainly determined by the spin-down channel and exhibit a large spin polarization. The conductance of three antiferromagnetic coupling states is nearly zero at the Fermi level. These theoretical results indicate that the novel 2D C3N monolayer is promising for molecular spintronics devices in the near future.

Highly Efficient and Tunable Filtering of Electrons' Spin by Supramolecular Chirality of Nanofiber-Based Materials.

Organic semiconductors and organic-inorganic hybrids are promising materials for spintronic-based memory devices. Recently, an alternative route to organic spintronic based on chiral-induced spin selectivity (CISS) is suggested. In the CISS effect, the chirality of the molecular system itself acts as a spin filter, thus avoiding the use of magnets for spin injection. Here, spin filtering in excess of 85% in helical π-conjugated materials based on supramolecular nanofibers at room temperature is reported. The high spin-filtering efficiency can even be observed in nanofibers assembled from mixtures of chiral and achiral molecules through chiral amplification effect. Furthermore and most excitingly, it is shown that both "up" and "down" orientations of filtered spins can be obtained in a single enantiopure system via the temperature-dependent helicity (P and M) inversion of supramolecular nanofibers. The findings showcase that materials based on helical noncovalently assembled systems are modular platforms with an emerging structure-property relationship for spintronic applications.

Endohedral Fullerene Fe@C28 Adsorbed on Au(111) Surface as a High-Efficiency Spin Filter: A Theoretical Study.

We present a theoretical study on the adsorption and spin transport properties of magnetic Fe@C28 using Ab initio calculations based on spin density functional theory and non-equilibrium Green’s function techniques. Fe@C28 tends to adsorb on the bridge sites in the manner of C–C bonds, and the spin-resolved transmission spectra of Fe@C28 molecular junctions exhibit robust transport spin polarization (TSP). Under small bias voltage, the transport properties of Fe@C28 are mainly determined by the spin-down channel and exhibit a large spin polarization. When compressing the right electrode, the TSP is decreased, but high spin filter efficiency (SFE) is still maintained. These theoretical results indicate that Fe@C28 with a large magnetic moment has potential applications in molecular spintronics.

Controlling the conductance of single-molecule junctions with high spin filtering efficiency by intramolecular proton transfer

Abstract The pursuit of miniaturization of magnetic electronic components spurs intensive theoretical and experimental researches on designing molecule-scale magnetic devices. Controlling the transport properties is one of the most vital focuses for magnetic molecular devices. In this work, magnetic devices constructed by a single epindolidione (Epi) molecule (5,11-dihydrodibenzo[b,g][1,5]naphthyridine-6,12-dione) bridging two zigzag graphene nanoribbon (zGNR) electrodes are theoretically designed. The Epi molecule can be converted between the keto and enol forms, which is confirmed by first principle molecular dynamics method. The influences of intramolecular proton transfer and the bridging manner between the core molecule and zGNR electrodes on the magnetic transport properties are investigated. Spin-resolved current-voltage (I-V) curves show that both the keto and enol devices display remarkable spin filtering effect. However, the effect of intramolecular proton transfer on the electron transport properties depends on the bridging manner between the Epi molecule and zGNR electrodes. When the Epi molecule is connected to zGNR electrodes with 4,7-sites (A bridging manner), the electron transport properties of molecular junctions are hardly affected by the intramolecular proton transfer. On the contrary, the conductance of the molecular junctions is significantly modulated by the intramolecular proton transfer when the Epi molecule is connected to zGNR electrodes with 4,4′-sites (B bridging manner). Further analysis reveals that the high spin filtering effect originates from stronger coupling between spin-up edge electronic states of zGNR electrodes and states of the core molecule. With B bridging manner, the conjugation characteristics of the Epi molecule as well as the transmission pathway of tunneling electrons can be largely modulated by the intramolecular proton transfer. Our work proposes a feasible way to control the conductance of single-molecule junctions by taking advantage of intramolecular proton transfer.

Theoretical Studies of the Spin-Dependent Electronic Transport Properties in Ethynyl-Terminated Ferrocene Molecular Junctions.

The spin-dependent electron transport in the ferrocene-based molecular junctions, in which the molecules are 1,3-substituted and 1,3′-substituted ethynyl ferrocenes, respectively, is studied by the theoretical simulation with nonequilibrium Green’s function and density functional theory. The calculated results suggest that the substitution position of the terminal ethynyl groups has a great effect on the spin-dependent current-voltage properties and the spin filtering efficiency of the molecular junctions. At the lower bias, high spin filtering efficiency is found in 1,3′-substituted ethynyl ferrocene junction, which suggests that the spin filtering efficiency is also dependent on the bias voltage. The different spin-dependent transport properties for the two molecular junctions originate from their different evolutions of spin-up and spin-down energy levels.

Spin-polarized transport properties in some transition metal dithiolene complexes.

Spin filtering materials are of great current interest in part due to their applications in molecular electronics. In this study, we carried out a theoretical investigation on the charge transport properties of transition metal (TM) dithiolene complexes with TM = Ni, Fe and Mn by using non-equilibrium Green's function/density functional theory (NEGF-DFT) methods. The characteristics of current-voltage and spin-resolved transmission spectra pointed out that Ni complexes are non-polarized, while Fe and Mn complexes exhibit high polarization and can be regarded as excellent candidates for spin-filtering materials with high spin-filtering efficiency. These differences were rationalized on the basis of electron delocalization over the molecular junction of the partial distribution of α- and β-spin molecular projected self-consistent Hamiltonian (MPSH) orbitals, and also the first eigenchannels of molecular junctions.

High spin-filter efficiency and Seebeck effect through spin-crossover iron-benzene complex.

Electronic structures and coherent quantum transport properties are explored for spin-crossover molecule iron-benzene Fe(Bz)2 using density functional theory combined with non-equilibrium Green's function. High- and low-spin states are investigated for two different lead-molecule junctions. It is found that the asymmetrical T-shaped contact junction in the high-spin state behaves as an efficient spin filter while it has a smaller conductivity than that in the low-spin state. Large spin Seebeck effect is also observed in asymmetrical T-shaped junction. Spin-polarized properties are absent in the symmetrical H-shaped junction. These findings strongly suggest that both the electronic and contact configurations play significant roles in molecular devices and metal-benzene complexes are promising materials for spintronics and thermo-spintronics.

Axisymmetric All-Carbon Devices with High-Spin Filter Efficiency, Large-Spin Rectifying, and Strong-Spin Negative Differential Resistance Properties

We propose the perfect all-carbon axisymmetric spintronic devices consisting of a zigzag-edged trigonal graphene (ZTG) linked to left and right zigzag-edged graphene nanoribbons (ZGNR) electrodes via carbon atomic chains (CACs). To ensure the stability of the system, the edge carbon atoms are passivated by hydrogen atoms. The self-consistent density functional theory (DFT) calculations show that the simple all-carbon system possesses the prefect spin-filtering property at a wide voltage region from −1.0 to 1.0 V. More importantly, the proposed system can act as a perfect dual spin diode in the antiparallel (AP) spin configuration, and the single-spin rectifying ratio can reach 103. When we add the number of the CACs linked to the left ZGNR electrode, the device shows the obvious single-spin negative differential resistance (NDR) behavior, which originates from the appearance of the localized states in the region of the left ZGNR electrode and ZTG. Meanwhile, the perfect spin-filtering and dual spin-diode ...

Electronic transport properties of (fluorinated) metal phthalocyanine

The magnetic and transport properties of the metal phthalocyanine (MPc) and F16MPc (M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn and Ag) families of molecules in contact with S–Au wires are investigated by density functional theory within the local density approximation, including local electronic correlations on the central metal atom. The magnetic moments are found to be considerably modified under fluorination. In addition, they do not depend exclusively on the configuration of the outer electronic shell of the central metal atom (as in isolated MPc and F16MPc) but also on the interaction with the leads. Good agreement between the calculated conductance and experimental results is obtained. For M = Ag, a high spin filter efficiency and conductance is observed, giving rise to a potentially high sensitivity for chemical sensor applications.

Rhenium-phthalocyanine molecular nanojunction with high magnetic anisotropy and high spin filtering efficiency

Using the density functional and non-equilibrium Green's function approaches, we studied the magnetic anisotropy and spin-filtering properties of various transition metal-Phthalocyanine molecular junctions across two Au electrodes. Our important finding is that the Au-RePc-Au junction has both large spin filtering efficiency (&amp;gt;80%) and large magnetic anisotropy energy, which makes it suitable for device applications. To provide insights for the further experimental work, we discussed the correlation between the transport property, magnetic anisotropy, and wave function features of the RePc molecule, and we also illustrated the possibility of controlling its magnetic state.

A new two-dimensional metal-organic framework with high spin-filtering efficiency.

Here we propose a family of two-dimensional organometallic lattices based on first principle calculations. The proposed lattice is designed by assembling molecular building blocks of a naphthalene molecule functionalized by -NH groups and transition metals which are surrounded by four -NH moieties, creating a square planar geometry. The predicted organometallic lattices (with Fe, Cr and Co) are shown to exhibit half metallicity and therefore this class of materials has great promise for application of spintronics.

Spin negative differential resistance and high spin filtering behavior realized by devices based on graphene nanoribbons and graphitic carbon nitrides

Using nonequilibrium Green’s functions in combination with the density functional theory, we investigate the spin-dependent electronic transport properties of two nanostructure devices based on graphitic carbon nitrides bridging two zigzag graphene nanoribbons, i.e., center and edge bridged devices, respectively. It is found that the center bridged device behaves spin negative differential resistance properties in different bias ranges for the up and down spin current respectively. The edge bridged device presents obvious negative differential resistance only for the down spin current. Moreover, high spin-filtering efficiency over 80% is obtained in the edge bridged device in the bias range of 0–1.0V. The magnetic properties of these devices suggest promising applications in spintronics and molecular electronics.

Improving spin-filtering efficiency in graphene and boron nitride nanoribbon heterostructure decorated with chromium-ligand

By applying nonequilibrium Green’s functions in combination with density-function theory, we investigate the spin-dependent transport properties of graphene and boron nitride nanoribbon heterostructure decorated with chromium-ligand. In the heterostructure, the graphene and boron nitride nanoribbon are connected in a interlaced way, and the chromium-ligand are decorated above the surface of the graphene nanoribbon. When one boron nitride nanoribbon fragment is embedded in the graphene nanoribbon, the maximum spin-filtering efficiency at finite bias is only about 65%. However, almost 100% spin-filtering efficiency can be observed at low bias when one more BNNR fragment is introduced into the system. Especially, the high spin-filtering efficiency is independent of the magnetic configuration of the device. Our work provides a new thinking to achieve the high-performance spin filter.

High-performance giant-magnetoresistance junctions based on the all-Heusler architecture with matched energy bands and Fermi surfaces

We present an all-Heusler architecture which could be used as a rational design scheme for achieving high spin-filter efficiency in the current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) devices. A Co2MnSi/Ni2NiSi/Co2MnSi trilayer stack is chosen as the prototype of such an architecture, of which the electronic structure and magnetotransport properties are systematically investigated by first principles approaches. Well matched energy bands and Fermi surfaces between the all-Heusler electrode-spacer pair are found, which, in combination with the electrode half-metallicity, indicate large bulk and interfacial spin-asymmetry, high spin-filter efficiency, and consequently good magnetoresistance performance. Transport calculations further confirm the superiority of the all-Heusler architecture over the conventional Heusler/transition-metal structure by comparing their transmission coefficients and interfacial resistances of parallel conduction electrons, as well as the macroscopic current-voltage characteristics. We suggest future theoretical and experimental efforts in developing high-performance all-Heusler CPP-GMR junctions for the read heads of the next generation high-density hard disk drives.

Non-magnetic doping induced a high spin-filter efficiency and large spin Seebeck effect in zigzag graphene nanoribbons

Based on nonequilibrium Green's functions (NGF) and density-functional theory (DFT), we investigate the magnetotransport properties and magnetothermoelectric effects in zigzag graphene nanoribbons (ZGNRs) with non-magnetic doping on the double ribbon edges. One of the carbon atoms without hydrogen saturation in each ribbon edge is replaced by one boron (B) or one nitrogen (N) atom. Compared with boron–boron (BB) and nitrogen–nitrogen (NN) double-edge doping, the boron–nitrogen (BN) double-edge doping induces a perfect spin-filter effect with 100% negative spin polarization at the Fermi level. Moreover, we find that the thermoelectric effect can be enhanced by the double-edge doping. Interestingly, the spin Seebeck effect in NN- and BN-doped ZGNRs becomes comparable with the charge Seebeck effect and even larger than it. These results originate from the spin-dependent transmission node near the Fermi level induced by the non-magnetic doping. These findings strongly suggest that the double-edge-doped ZGNRs are promising materials for spintronics and thermo-spintronics.