Proximity-induced spin filtering in vdW CrSBr spin-valves with ZrTe5 barriers.

Current spin polarization and spin injection efficiency in ZnO-based ferromagnetic semiconductor junctions

Graphene nanodisks (GNDs) have attracted significant attention due to their unique electronic and magnetic properties, offering promising prospects for applications in nanoelectronics and spintronic devices. In this study, we investigate the density of states (DOS), spin currents, and spin polarization characteristics of pristine and Co-doped diamond-shaped and triangular GNDs using first-principles calculations. Our results reveal that Co doping induces spin splitting within the band gap of diamond-shaped GNDs, indicating spin-dependent phenomena. Additionally, fine spin splitting and metallic behavior are observed in the DOS of triangular GNDs. Through I-V curve analysis, we demonstrate that Co-doped diamond-shaped GNDs exhibit spin switch behavior and polarized spin currents, with a notable increase in peak current and polarization compared to pristine GNDs. The introduction of Co impurities enhances the spin filtering capabilities, making the device act as a spin filter in a wide voltage range. These findings provide valuable insights into the electronic and spintronic properties of Co-doped GNDs, offering possibilities for the development of efficient spintronic devices and spin filtering applications.

Spin-polarized quantum transport in Fe4N based current-perpendicular-to-plane spin valve

Efficient spin injection is essential for the development of ferromagnet—semiconductor spintronic devices with high performances, including spin transistors. Although the Co2Fe(Al0.5,Si0.5) (CFAS)/Ge hybrid structure has been identified as an outstanding platform for such devices, there is a lack of systematic analyses on the effects of the interface atomic structure on the spin-electronic properties. In this study, we investigate electronic and magnetic properties of CFAS/Ge (001) interfaces by density functional theory calculations under two possible scenarios, with atomically abrupt bulk-like interfaces and with intermixing at the interfaces. For two possible terminations in the case of abrupt interfaces, we show considerable reductions in spin polarization (SP), which is emphasized in the case of the —Fe—Si,Al/Ge interface, where the SP has reversed sign. Further, we show that Fe—Ge interdiffusion is most likely to occur at the interface, and that this intermixing does not largely affect the spin-electronic properties. In contrast, the model of interdiffusion affecting the Co sublattice in the CFAS film exhibits a reversed SP at the interface layers, but this is less likely to occur owing to the higher energy for such atomic swaps. Band alignment analyses show that interfaces with a small degree of Fe/Ge intermixing could be beneficial for the spin injection efficiency. This study demonstrates that the spin injection efficiency is strongly dependent on the ferromagnet—semiconductor interface atomic structure, and thus can guide further theoretical and experimental studies for development of spintronic devices with improved properties.

Optoelectronically controlled transistor and magnetoresistance effect in an antiferromagnetic graphene-based junction

We theoretically study the electron transport properties in a ferromagnetic/normal/ferromagnetic tunnel junction, which is deposited on the top of a topological surface. The conductance at the parallel (P) configuration can be much bigger than that at the antiparallel (AP) configuration. Compared P with AP configuration, there exists a shift of phase which can be tuned by gate voltage. We find that the exchange field weakly affects the conductance of carriers for P configuration but can dramatically suppress the conductance of carriers for AP configuration. This controllable electron transport implies anomalous magnetoresistance in this topological spin valve, which may contribute to the development of spintronics. In addition, there shows an existence of Fabry-Perot-like electron interference in our model based on the topological insulator, which does not appear in the same model based on the two dimensional electron gas.

The field of magnetoelectronics has been growing in practical importance in recent years1. For example, devices that harness electronic spin—such as giant-magnetoresistive sensors and magnetoresistive memory cells—are now appearing on the market2. In contrast, magnetoelectronic devices based on spin-polarized transport in semiconductors are at a much earlier stage of development, largely because of the lack of an efficient means of injecting spin-polarized charge. Much work has focused on the use of ferromagnetic metallic contacts3,4, but it has proved exceedingly difficult to demonstrate polarized spin injection. More recently, two groups5,6 have reported successful spin injection from an NiFe contact, but the observed effects of the spin-polarized transport were quite small (resistance changes of less than 1%). Here we describe a different approach, in which the magnetic semiconductor BexMnyZn1-x-ySe is used as a spin aligner. We achieve injection efficiencies of 90% spin-polarized current into a non-magnetic semiconductor device. The device used in this case is a GaAs/AlGaAs light-emitting diode, and spin polarization is confirmed by the circular polarization state of the emitted light.

First-principles investigations are performed on magnetic tunnel junctions (MTJs) constructed with chromium trihalide CrCl3 as barrier and half metallic ferromagnet (HMF) CrO2 as electrodes using density function theory (DFT) calculations, and the results are compared with CrBr3 and CrI3. On comparing the results obtained after performing the first-principles investigation on CrCl3, CrBr3, and CrI3, it is understood that CrCl3 offers very high tunnel magnetoresistance (TMR) of ~ 100% and spin injection efficiency (η) of ~ 100% for different bias voltages, and spin transport occurs due to tunneling which is evident from the transmission spectrum. Although CrBr3 has TMR greater than 95% and spin injection efficiency (η) of ~ 100%, transmission states are present at the Fermi level, hence, tunneling is not the phenomenon in the case of CrBr3. CrI3 suffers from fluctuations in both TMR and spin injection efficiency (η) over the applied bias voltage range and has more spin-up current and spin-down current in both parallel configuration and anti-parallel configuration. In CrI3, as there are states in transmission spectrum at the Fermi level, the spin transport occurs because of band-to-band hopping instead of tunneling. From the results obtained, CrCl3 is identified as the perfect material to be used as the barrier in MTJs.

Electronic, magnetic, and topological properties of layered ternary chalcogenide CoAsS: A first principles study

Spin-dependent transport through a quantum-dot (QD) ring coupled to ferromagnetic leads with noncollinear magnetizations is studied theoretically. Tunneling current, current spin polarization and tunnel magnetoresistance (TMR) as functions of the bias voltage and the direct coupling strength between the two leads are analyzed by the nonequilibrium Green's function technique. It is shown that the magnitudes of these quantities are sensitive to the relative angle between the leads' magnetic moments and the quantum interference effect originated from the inter-lead coupling. We pay particular attention on the Coulomb blockade regime and find the relative current magnitudes of different magnetization angles can be reversed by tuning the inter-lead coupling strength, resulting in sign change of the TMR. For large enough inter-lead coupling strength, the current spin polarizations for parallel and antiparallel magnetic configurations will approach to unit and zero, respectively.PACS numbers:

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.

Designing devices with excellent spin-polarized properties has been a challenge in physics and materials science. In this work, we report a theoretical investigation of the spin injection and spin-polarized transport properties of monolayer and bilayer phosphorene devices with Co electrodes. Based on the analysis of transmission coefficients, spin-polarized current, magnetoresistance (MR) (or tunnel MR) ratio and spin injection efficiency (SIE), both devices show superior spin-polarized transport properties. As phosphorene in the device is changed from monolayer to bilayer, the charge carrier type can be tuned from n-type to p-type. For the monolayer phosphorene device, the tunnel MR ratio reaches about 210% and the SIE is about 80.7% at zero bias. Notably, the SIE and tunnel MR ratio maintain almost constant values against bias voltage and gate voltage, which makes it suitable for magnetic sensors. As for the bilayer phosphorene device, it not only exhibits a considerable tunnel MR ratio, but also shows significantly enhanced conductance, beneficial to the sensitivity of spintronic devices. Further analysis shows that the improvement of conductance is attributed to the low barrier height between the bilayer phosphorene channel and Co electrodes. According to our results, the studied phosphorene devices with Co electrodes demonstrate superior spin injection and transport properties. We believe that these theoretical findings will be a strong asset for future experimental works in spintronics.

Magnetic and electronic properties of a single iron atomic chain encapsulated in carbon nanotubes: A first-principles study

Until recently, mainstream electronics was exclusively based on charge proper- ties. Apart from charge, an electron also possesses an intrinsic angular momen- tum (spin), and directly coupled to that a magnetic moment. A newly emerg- ing approach is to use this extra spin degree of freedom to provide additional performance and functionality in widely used commercial applications, although nowadays mostly in metallic structures. Semiconductors are of great interest for future spin-based electronics because of the predicted longer spin coherence. The ability to electrically inject, manipulate, and detect spin polarized carriers within the active semiconductor are essential components from the integration point of view for such a technology. Transport of spin polarized carriers is commonly demonstrated by a speci¯c resistance change as function of the external applied magnetic ¯eld (magnetoresistance). The realization of all electrical spin injection and detection in an inorganic (GaAs) and in an organic (Alq3) semiconductor will be the focus of this thesis. Besides, observed large magnetoresistance e®ects in silicon from di®erent origin will be extensively discussed. Before we address the experimental aspects of the hybrid semiconductor de- vices, a detailed theoretical analysis has been performed to the feasibility of all electrical spin injection and detection in semiconductors by means of ferro- magnetic electrodes and including spin-selective interface barriers to overcome the impedance mismatch. Based on the Poisson and the di®usion equation, in- cluding electric ¯eld e®ects, the expected resistance di®erence for parallel and anti-parallel magnetization alignment of the ferromagnetic electrodes has been analytically calculated. The in°uence of the sample and measurement geom- etry has been extensively investigated and the results will be used within our experimental design analysis. Moreover, we propose a new lateral measurement geometry for which the magnetoresistance closely approaches the magnetoresis- tance value obtained for a vertical device. Electric ¯elds created in di®erent regions via separate bias voltages minimizes the spin loss in the semiconductor side branches of the lateral device. Our ¯rst experimental device consists of electron-beam-lithography processed ferromagnetic electrodes crossing a GaAs transport channel. Although silicon is the industrially most relevant semiconductor, GaAs has been chosen for its di- rect band gap, which enables optical investigations of the spin polarization in our group. Control over the magnetization alignment of the electrodes is established via an external applied magnetic ¯eld. Di®erent switching ¯elds for di®erent electrode widths have been measured by magnetic force microscopy. Towards observation of magnetoresistance due to spin transport, we show that the dop- ing pro¯le under the ferromagnetic contacts and in the semiconductor transport channel is of critical importance for the e®ective detection and depolarization of the carriers. Organic semiconductors pro¯t from their °exibility and the ease of process- ing. While these synthetic organic materials are exploited for their tunability of charge-carrier transport properties, their spin transport properties form a less explored area. Spin transport through a hybrid Al2O3(1.5 nm)/Alq3 barrier has been studied as a function of the thickness of the organic (0-6 nm) layer at room temperature. From the current-voltage behavior we conclude that for hybrid bar- riers with more than 2 nm Alq3, transport by multiple step tunneling dominates over transport by direct tunneling. Because of weak spin-orbit interaction at the intermediate molecular site and a possible low hopping rate, spin should be sensitive to small local ¯elds, in particular the total hyper¯ne ¯eld originating from the local hydrogen nuclei. We suggest that in the regime of multiple step tunneling, hyper¯ne coupling could be a relevant source of spin randomization and could modify the characteristic hysteretic magnetoresistance by a symmetric contribution. A possible ¯ngerprint is indeed observed in our experiment. Silicon holds exceptional promise for spin-based electronics, by virtue of its compatibility with the current CMOS technology. As a possible implicit contri- bution to future silicon-based spintronics devices or as a magnetoresistive sensor, boron-doped Si-SiO2-Al structures are fabricated to study extremely large mag- netoresistance e®ects. Current-voltage characteristics show a strong non-linear behavior, dominated by an autocatalytic process of impact ionization. At low temperatures, the magnetic ¯eld postpones the onset of impact ionization to higher electric ¯elds. This results in a symmetric positive magnetoresistance of over 10,000% at magnetic ¯elds of 400 kA/m. A macroscopic transport model is introduced that is able to describe how the magnetoresistance is controlled by voltage, electrode spacing and oxide thickness. Utilizing that the e®ect of a magnetic ¯eld on an acceptor wave function becomes stronger with increas- ing distance from the impurity, we present a room temperature constant voltage magnetoresistance of over 1000% at 1 MA/m in low doped silicon.

In this paper we propose a spin detector based on the exchange interaction between the conduction electrons and a nearby spin array. The device structure is very close to a spin-valve device in an anti-parallel (AP) configuration. We show that in such a structure, the spin information can be obtained from the second derivative of the current. Our calculations based on realistic device parameters show that as small as a single spin should be detectable with a very high spatial resolution. Ideal half-metallic contacts would give the optimum performance for the proposed detector. However, when spin-injection efficiency is limited, we show that using an appropriate de-embedding scheme, the spin information can still be retained.