Spin-filter Devices Research Articles

Thermoelectric and optoelectronic features of C- and N- doped CsZnBr3 halide perovskite for use in spin filter and energy efficient devices

Present study reports mainly thermoelectric and optical properties followed by its structural, electronic, magnetic properties of CsZnBr3 halide perovskite using full potential linearized augmented plane wave method in the framework of density functional theory. Further we analyzed the impact of C and N on CsZnBr3 for their electronic structure, magnetic nature, thermoelectric, and optical properties. CsZnBr3 under optimum conditions exhibits a non-magnetic phase, which interestingly upon doping of C and N, turns out to be ferromagnetic with magnetic moments of 3.0 and 2.0 μB for CsZnBr2C and CsZnBr2C, respectively. Furthermore, Semiconducting CsZnBr3 exhibits spin filter semiconductor nature with energy band gaps of 1.38↑ and 3.26↓ eV for CsZnBr2C and 2.72↑ and 1.67↓ eV for CsZnBr2N. These doped materials can be used in spintronics as spin-filter devices for lower power consumption leading to more energy-efficient electronics. The thermoelectric parameters as Seebeck coefficient, power factor, thermal conductivity and figure of merit are estimated using BoltzTrap code. The figure of merit value found enhanced from 0.88 to 1.06 with one orientation of spins for CsZnBr2C at high temperature, which suggests its potential use in thermoelectric applications. In optical reference photon energy can be absorbed in UV-region.

Spin filtering and quantum transport with transition metal-doped hydrogenated silicon quantum dot

Spin filtering is a fundamental operation in spintronics, enabling the generation and detection of spin-polarized carriers. Here, we proposed and theoretically demonstrated that a 3d transition metal (TM) doped hydrogenated silicon quantum dot (TM:H-SiQD) is a suitable candidate for spin-filter devices. Using density functional theory, we investigate the structure, electronic properties, and magnetic behavior of TM:H-SiQD. Our calculations demonstrate that Mn:H-SiQD exhibits the highest stability. The designed spin-filter device using Mn:H-SiQD shows a spin-filtering efficiency of 99.9% at 300 K electrode temperature along with very high conductance. This remarkable efficiency positions it as a promising candidate for spintronic devices.

Spin-filter device using the Zeeman effect with realistic channel and structure parameters

We have theoretically calculated the performance of a Zeeman-type spin polarizer, which consists of ferromagnetic (FM) and metal–insulator–semiconductor (MIS) gate nanostructures on top of an InAs two-dimensional electron gas (2DEG) channel. For the calculations, we have taken a realistic electron concentration, electron effective mass and the effective g-factor of the InAs 2DEG into account. In addition, we have assumed realistic FM and MIS structure sizes by conventional electron beam lithography. In the calculations, we have demonstrated clear oscillation of spin polarization over ±85%. Furthermore, we have shown that it works not only as a spin-polarized current generator but also a detector. In addition, we have proposed a novel spin-filter device utilizing the Zeeman-type spin polarizers. We have found that its conductance characterization allows us to evaluate the operation of Zeeman-type spin polarizers. We expect the Zeeman-type spin polarizers and spin-filter devices to open up a new field of spintronics.

Manipulation of quantum spin transport of TM (Mn, Fe, Co, and Ni) (II) phthalocyanines coupled to carbon nanotube leads applicable in spintronic devices

We conducted a theoretical scrutiny on the quantum spin transport characteristics of a class of open-shell 3d-transition metal (TM = Mn, Fe, Co, and Ni) (II) phthalocyanines (TMPcs) molecules sandwiched between two semi-infinite armchair single-walled carbon nanotube probes. Herein, the spin density functional formalism is utilized in conjunction with state-of-the-art non-equilibrium Green's function technique. Molecular junctions composed of MnPc and FePc have higher local magnetic spin moments than CoPc and NiPc because of the strong exchange spin-splitting between the 3d-states of the Mn or Fe cation atoms and the p-states of the N anion atom. This indicates that TMPc molecules (TM = Mn, and Fe) bridged between two single-walled carbon nanotube (SWCNT) electrodes with a π-type geometry demonstrate a pronounced transmission near the Fermi level. Furthermore, the sign and robustness of spin filter efficiency are tailored by manipulating the central atom of 3d-transition metal and the contact SWCNT electrodes. Subsequently, FePc and MnPc molecular junctions have the advantage of operating practically as ideal spin filter devices compared to CoPc and NiPc molecular structures. Moreover, the tunneling magnetoresistance (TMR) of these molecular devices is assessed. For MnPc and FePc molecular junctions, the estimated total conductance exhibited a robust trend at zero bias voltage, whereas the magnitudes of spin-up and spin-dn quantum conductances increased significantly in CoPc and NiPc molecular configurations with bias voltages range between ±0.45 and ±0.95 Volt. Spin-down carriers essentially govern the quantum conductance of TMPc (Mn, Fe, Co, and Ni) molecular junctions at bias voltage around ±0.75 Volt. By examining their I-V characteristics, it has been established that MnPc, and FePc molecular junctions exhibit metal-like behavior, whereas CoPc and NiPc molecular devices are subject to negative differential resistance. As a result of our theoretical findings, it is found that TMPcs (TM = Fe, Mn) coupled to SWCNT probes yield a robust spin filter efficiency that may be of interest for prospective technological realizations in organic-inorganic molecular spintronic devices.

Modulating spintronic properties of transition metals doped GaN nanotubes with high Curie temperature

AbstractBetween the ferromagnetic semiconductors of the III‐V group, the transition metals (TMs) doped gallium nitride (Ga, TM)N diluted magnetic semiconductor (DMS) shows the most well‐understood and promising applications in spintronic, due to its high Curie temperature. In this research, electronic and magnetic properties of pure armchair (3, 3) and zigzag (5, 0) gallium nitride nanotubes (GaNNTs) and doped with TMs are investigated using the spin‐polarized density functional theory. The spin‐polarized DOS revealed that pure zigzag and armchair GaNNTs are nonmagnetic semiconductors with a direct and indirect bandgap, respectively, in contrast, TMs doped GaNNTs are DMS or half metals (HM). Our results show a high Curie temperature of more than 823 K for Cr and Mn doping, indicating may be good room‐temperature ferromagnetic material for spintronic applications in the future. 11% Cr and Mn atoms doped (3, 3) GaNNT are HM with 100% spin polarization and appear to be good candidates for spintronic applications and especially as spin filter devices.

Transition metals doped (3,3) armchair boron nitride nanosheet as dilute magnetic semiconductors materials for the spintronic application

AbstractMagnetic 2D materials have attracted considerable attention for their significant potential application in spintronic. In this work, the effect of substitutional doping of 3d‐transition metals such as Co, Cr, Mn, and Fe on the magnetic and electronic properties of boron nitride nanosheet (BNNS) was studied based on the spin‐polarized density functional theory. The results revealed that the non‐magnetic and semiconducting behavior of BNNS can be altered by magnetically active dopants. The spin‐polarized density of states suggests that pure BNNS is a nonmagnetic semiconductor with a direct bandgap while transition metals doped BNNS are dilute magnetic semiconductors or half metals (HM). Co doping shows the most stable ferromagnetic phases in the nanosheet. A pair of Mn and Co atoms doped BNNS in edge structure show HM property with 100% spin polarization and seem to be good candidates for spintronic applications and especially as spin filter devices and spin current injectors.

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.

Spin polarization rate calculation for T-shaped double quantum dots coupled to (C- terminated ScC(1 1 1) surface) leads

The device considered in our study is the T-shaped double quantum dots system embedded between two ferromagnetic (C-terminated ScC (111) surface) leads. The theoretical treatment is achieved using the time-evolution operator approach. The role of the time-dependent external field, spin-dependent coupling interaction and energy spacing on the dots in spin transport through the device considered in our study has studied. The spin accumulation on the quantum dots, the spin and total currents and the spin polarization rate of the device have calculated. The imprint of the leads density of states is very obvious in the time window calculation which increases with the energy spacing and the frequency of the time-dependent external field. Our results indicate that time-dependent external field and spin-dependent coupling interaction play important role in manufacturing full spin polarization and controlling the spin polarization rate in the device. Controlling the spin transport features have many potential applications in spin-based quantum devices such as quantum computing and spin filter devices.

Spin-Filter Devices Based on Resonant Magnetic Tunnel Junctions

Spin-polarized currents are investigated in symmetric (asymmetric) resonant magnetic tunnel junctions (S- (A)-RMTJs) including a non-magnetic metal (NM) layer. Charge-diode and spin-diode features are found for the S-RMTJs at definite thicknesses of MgO and NM layers. Owing to the presence of quantum-well states, a full spin polarization can be achieved by proper choice of the thickness of NM layer. The charge and spin currents have increased for the A-RMTJs in comparison to those of the S-RMTJs due to different properties of ferromagnetic electrodes. The present study suggests new spin-filter devices to use in the spintronics field.

Spin-filtering effects of double-barrier magnetic tunnel junctions with an indium phosphide (InP) spacer

Spin-polarized currents in double-barrier magnetic tunnel junctions (MTJs) as CoFeB/MgO/InP/MgO/CoFeB (MTJs-InP) are investigated by non-equilibrium Green’s function formalism. The asymmetric structures with a half-metal LSMO contact are studied and a spin-diode behavior is found compared to the MTJs-InP. Charge and spin currents as well as spin polarization as a function of bias voltage, angle between magnetizations and quantum-well thickness are also described. A nearly 100% spin polarization is observed at a certain range of bias voltage. Therefore, one can design excellent spin-filter devices based on new MTJs-InP.

Magnetic field effect on spin-polarized transport in asymmetric multibarrier based on InAs/GaAs/GaSb systems

This paper investigates how an applied magnetic field, the quantum size, and spin polarization effect an asymmetric heterostructure composed of InAs, GaAs, and GaSb semiconductors. Using a theoretical approach based on the transfer matrix method and taking into account the Rashba and Dresselhaus spin-orbit interactions, we calculate the spin-dependent transmissions of spin-up and -down electrons and their spin polarization across our heterostructure. Our results indicate that the transmission coefficients and the resonance states can be tuned to a red or blue shift by adjusting the quantum wells and the barrier widths. Two resonance states are detected when the width of the central barrier Lbc is reduced. Furthermore, we show that the impact of an applied magnetic field on the spin polarization can polarize 100% of either spin -up or -down electrons by selecting the appropriate range of incident energy and suitable magnetic field. These results are useful for the design and fabrications of spin-filter devices operating under an applied magnetic field.

Proteomic Protocols for Differential Protein Expression Analyses.

Protocols are described for preparation of various types of samples for differential protein expression proteomics using nano liquid chromatography-tandem mass spectrometry (nLCMS/MS). Fresh frozen tissue, formalin-fixed paraffin-embedded (FFPE) tissue, cells, pull-downs, immunoprecipitations, and plasma or serum can be processed. For transplantation studies, it should be noted that samples must be comparable; thus, similar cells or organ systems from the same species can be compared when only a minority of the proteins change expression levels. For xenotransplantation studies, caution should be taken, as different species possess proteins with differences in primary structure. The sample preparation technique is based on spin filter devices using sodium deoxycholate (SDC) as detergent for extraction of proteins. The detergent is removed using phase extraction with ethyl acetate, and samples can be used for label-free quantification (LFQ) analysis or peptides can be labeled with tandem mass tags (TMT).

Embedded quantum dots in semiconductor nanostructures

In this work, we report the behavior of the tunneling current in a semiconductor nanostructure of (Ga, Al)As/GaAs which takes into account the behavior of the electrons and the Rashba’s spin orbit interaction in the presence of embedded quantum dots of different geometries (lens, pyramid and ring) in voltage function, magnetic field, and the different values of the interaction spin orbit (π/2, π/4 and 3π/4). The results that were obtained show, that the intensity of the current presents appreciable changes when is changed the configuration of the quantum dot as the intensities of external fields and spin polarization as well. All these internal and external effects that are studied in our model, significantly modify the transport of information of the semiconductor nanostructure, our results show that the spin effects and the quantum dot configuration contribute to the quantum memories efficiency and the spin filter devices of actual use on nanoscience and nanotechnology.

Designing of spin filter devices based on zigzag zinc oxide nanoribbon modified by edge defect**Project supported by the National Natural Science Foundation of China (Grant Nos. 61664008 and 11604286) and the Scientific Technological Innovation Team of Yan’an City, China (Grant No. 2017CXTD-01).

The spin-dependent electronic transport properties of a zigzag zinc oxide (ZnO) nanoribbon are studied by using density functional theory with non-equilibrium Green’s functions. We calculate the spin-polarized band structure, projected density of states, Bloch states, and transmission spectrum of the ZnO nanoribbon. It is determined that all Bloch states are located at the edge of the ZnO nanoribbon. The spin-up transmission eigenchannels are contributed from Zn 4s orbital, whereas the spin-down transmission eigenchannels are contributed from Zn 4s and O 2p orbitals. By analyzing the current–voltage curves for the opposite spins of the ZnO nanoribbon device, negative differential resistance (NDR) and spin filter effect are observed. Moreover, by constructing the ZnO nanoribbon modified by the Zn-edge defect, the spin-up current is severely suppressed because of the destruction of the spin-up transmission eigenchannels. However, the spin-down current is preserved, thus resulting in the perfect spin filter effect. Our results indicate that the ZnO nanoribbon modulated by the edge defect is a practical design for a spin filter.

Spin Seebeck Effect in a Multiple Quantum Dot Molecule with Spin-Dependent Interdot Coupling

We study the spin Seebeck effect in a circularly connected triple quantum dot (TQD) structure taking the spin-dependent interdot coupling and magnetic flux into consideration. Particular attention is paid on the generation and manipulation of the 100% spin-polarized and pure spin thermopowers, which denote the arisen spin voltage in response of an infinitely small temperature gradient applied across the system. This can be realized by adjusting the peaks’ positions in the spin-up and spin-down thermopowers with the help of the spin polarization of the interdot couplings. At low temperature, a large value of pure spin thermopower is obtained even under very weak spin polarization of the interdot coupling. Strong spin polarization of it is favorable for 100% spin-polarized thermopower whose magnitude can reach as large as that of the charge one. We also find that a sign change of the considered two quantities can be realized by adjusting the magnetic flux penetrating through the TQDs. The present results could be useful in designing high-efficiency pure spin energy conversion and spin filter devices.

Electronic structure and magnetic ordering of NiN and Ni2N from first principles

The results of first-principles electronic structure calculations for the nitrogen-rich nickel nitrides and are presented. The calculations are based on density functional theory and used the generalized gradient approximation (GGA) as well as the GGA+U approach. The latter turned out to be crucial for a correct description of the crystal phase stability and magnetic instabilities of both compounds. While for GGA calculations predict a non-magnetic ground state with the zincblende structure, GGA+U calculations result in a half-metallic ferromagnet with the rocksalt structure in line with indications from the neighboring transition-metal nitrides making a possible candidate for spin-filter devices. For GGA calculations likewise lead to a non-magnetic behavior, which is contrasted with a ferrimagnetic ordering obtained from the GGA+U approach. This ground state results from complex three-dimensional exchange interaction via -type and -type overlap of the Ni 3d orbitals with the N 2p orbitals and may explain the reported sensitivity of the magnetic ordering to details of the crystal structure. For both nitrides, experimental data are called for to confirm our predictions.

Magnonic heat transport in the Lieb lattice

In this article we report the effect of charged impurity doping on the thermal spin-wave excitations of 2D Lieb lattice using the longitudinal/transverse and in-plane magnonic heat transport properties in a systematically Green’s function approach and the Born approximation. We present numerical results for XY Heisenberg model. Accordingly, the flow of magnonic current is enhanced depending on the impurity concentration, in which (i) at very low and very high concentrations, in-plane magnon conductivity becomes negative, (ii) the magnon Seebeck coefficient decreases (increases) before (after) a critical impurity concentration for both longitudinal/transverse and in-plane components, (iii) the longitudinal/transverse magnon thermal conductivity increases slightly with impurity concentration, while the in-plane one becomes flat, and (iv) both longitudinal/transverse and in-plane magnonic heat transport efficiencies decrease (increase) at low (high) temperatures with low impurity concentrations, whereas become flat (decrease) at high impurity concentrations. Our results are useful for the implementation of a new spin energy conversion and capable spin-filter devices for the spintronic community.

Time-dependent multiple barriers of the electric and exchange fields in silicene-like nanoribbons

We study the transport properties of the silicene nanoribbons subject to periodically driving electric and exchange fields. The multiple barriers made up of corresponding fields reshape the DC conductance by imposing pronounced both Fabry–Perot- and Fano-type resonances accompanied with high spin polarizations. In particular, a transport gap can be generated by the electric barriers with an appropriate strength, which is absent in the case of the barriers of the exchange field. The effects of the hybrid barriers including both electric and exchange fields, however, are not simply a mixture of two individual barriers, while depend on the relative phase of the time-varied barriers. In contrast to static barriers, the further studies of the driving frequency indicate that the in-gap states can survive in the transport gap for electric barriers as the frequency increases. This feature is particularly valuable for building spin-filter or spin-switcher devices.

Asymmetrical edges induced strong current-polarization in embedded graphene nanoribbons

We investigate the electronic structures and transport properties of the embedded zigzag graphene nanoribbon (E-ZGNR) in hexagonal boron nitride trenches, which are achievable in recent experiments. Our first principles results show that the E-ZGNR has a significant enhanced conductivity relative to common ZGNRs due to the existence of asymmetrical edge structures. Moreover, only one spin-orientation electrons possess a widely opened band gap at the magnetic ground state with anti-ferromagnetic configuration, resulting in a full current-polarization at low bias region. Our findings indicate that the state-of-the-art embedding technology is quite useful for tuning the electronic structure of ZGNR and building possible spin injection and spin filter devices in spintronics.

Designing lateral spintronic devices with giant tunnel magnetoresistance and perfect spin injection efficiency based on transition metal dichalcogenides.

Giant tunnel magnetoresistance (TMR) and perfect spin-injection efficiency (SIE) are extremely significant for modern spintronic devices. Quantum transport properties in a two-dimensional (2D) VS2/MoS2/VS2 magnetic tunneling junction (MTJ) are investigated theoretically within the framework of density functional theory combining with the non-equilibrium Green's functions (DFT-NEGF) method. Our results indicate that the designed MTJ exhibits a TMR with a value up to 4 × 103, which can be used as a switch of spin-electron devices. And due to the huge barrier for spin-down transport, the spin-down electrons could hardly cross the central scattering region, thus achieving a perfect SIE. Furthermore, we also explore for the effect of bias voltage on the TMR and SIE. We find that the TMR increases with the increasing bias voltage, and the SIE is robust against either bias or gate voltage in MTJs, which can serve as effective spin filter devices. Our results can not only give fresh impetus to the research community to build MTJs but also provide potential materials for spintronic devices.