Field Of Spintronics Research Articles

Effect of Alkaline Earth Metals Doping on the Electronic Structure, Magnetic and Optical Properties of g-SiC Monolayer System by First Principles Calculation

The band structure, electronic, magnetic, and optical properties of g-SiC monolayers doped with alkaline earth metals (Be, Mg, Ca, Sr, and Ba) are calculated by means of first principles based on density functional theory. Although the intrinsic g-SiC monolayer is nonmagnetic, it shows magnetic properties after doping with alkaline earth metals. The magnetic moments are, in the order of the above-named dopants, 1.583 μ B, 1817 μ B, 2.000 μ B, 2.000 μ B, and 2.000 μ B. Charge transfer and the net spin charge occur mainly between the dopant atom and surrounding C atoms. The results show that the conductivity of g-SiC can be greatly improved by doping with alkaline earth metals, a technique that can be applied to the field of semiconductor spintronics. High absorption peaks in the ultraviolet indicate that the material has potential applications in UV optoelectronic devices.

Magnetic proximity effect at the interface of two-dimensional materials and magnetic oxide insulators

Two-dimensional (2D) materials provide a platform for developing novel spintronic devices and circuits for low-power electronics. In particular, inducing magnetism and injecting spins in graphene have promised the emerging field of graphene spintronics. This review focuses on the magnetic proximity effect at the interface of 2D materials and magnetic oxide insulators. We highlight the unique spin-related phenomena arising from magnetic exchange interaction and spin-orbital coupling in 2D materials coupled with magnetic oxides. We also describe the fabrication of multifunctional hybrid devices based on spin transport. We conclude with a perspective of the field and highlight challenges for the design and fabrication of 2D spintronic devices and their potential applications in information storage and logic devices.

Tailoring magnetism in silicon-doped zigzag graphene edges

Recently, the edges of single-layer graphene have been experimentally doped with silicon atoms by means of scanning transmission electron microscopy. In this work, density functional theory is applied to model and characterize a wide range of experimentally inspired silicon doped zigzag-type graphene edges. The thermodynamic stability is assessed and the electronic and magnetic properties of the most relevant edge configurations are unveiled. Importantly, we show that silicon doping of graphene edges can induce a reversion of the spin orientation on the adjacent carbon atoms, leading to novel magnetic properties with possible applications in the field of spintronics.

Aspects of long range spin–triplet correlations in superconductor/ferromagnet hetero-structures

The notion of competing ferromagnetic (F) and superconducting (S) orders in F/S hybrid structures was transformed by the first realization of ferromagnetic Josephson π-junctions and the almost simultaneous prediction of a possibility of spin–triplet correlations in such structures, almost two decades back. Such hybrid structures in various configurations are now studied as rich sources of emergent states and new effects. Unlike the spin singlet Cooper pairs, the spin triplet Cooper pairs are much less affected by the exchange field of a ferromagnet and, therefore, immediately finds interest in the field of spintronics. Theoretically, it has been shown that the basic protocol for spin–singlet to spin–triplet supercurrent conversion is the presence of magnetic non-collinearity at the superconductor–ferromagnet interface. Therefore, almost all experiments in this direction have utilized transport measurements on F/S systems with artificial magnetic non-collinearity formed by combination of several ferromagnetic layers next to the superconducting layer. Here we highlight two aspects of studying these heterostructures. Firstly we show that natural magnetic inhomogeneities, found in domain walls of ferromagnets, can also be used to achieve singlet–triplet conversion, instead of artificial magnetic inhomoheneities. This possibility was explored via transport measurements in nano-scale planar Nb–Ni–Nb junctions and nano-SQUIDs, where a domain wall was pinned at the Josephson junction barrier. By this method we were able to show Josephson coupling across about 70 nm of strong ferromagnetic planar barrier. Secondly we show that spin–triplet correlations at the F/S interface are robust enough to be probed by the diamagnetic screening currents at the interface. This was probed by studying the change in sperconducting transition temperature of Nb/Co/Py/Nb multilayers in presence of small in-plane magnetic field. The Co/Py combination, which is a soft-hard type magnetic exchange spring, worked as magnetic inhomogeneity for triplet generation at the interface of the superconducting Nb. These observations may promote new experiments in the field of superconducting-spintronics.

Rashba-Edelstein Effect in the h-BN Van Der Waals Interface for Magnetization Switching.

Van der Waals materials are attracting great attention in the field of spintronics due to their novel physical properties. For example, they are utilized as spin-current generating materials in spin-orbit torque (SOT) devices, which offers an electrical way to control the magnetic state and is promising for future low-power electronics. However, SOTs have mostly been demonstrated in vdW materials with strong spin-orbit coupling (SOC). Here, the observation of a current-induced SOT in the h-BN/SrRuO3 bilayer structure is reported, where the vdW material (h-BN) is an insulator with negligible SOC. Importantly, this SOT is strong enough to induce the switching of the perpendicular magnetization in SrRuO3 . First-principles calculations suggest a giant Rashba effect at the interface between vdW material and SrRuO3 (110)pc thin film, which leads to the observed SOT based on a simplified tight-binding model. Furthermore, it is demonstrated that the current-induced magnetization switching can be modulated by the electric field. This study paves the way for exploring the current-induced SOT and magnetization switching by integrating vdW materials with ferromagnets.

Tuning the electronic and magnetic properties of O Vacancy and nonmetallic atoms doped monolayer SnO: A first-principles study

Using first-principles calculations, we systematically investigate the geometric structure, electronic structure and magnetic properties of bulk and monolayer Tin monoxide (SnO), as well as the influence of O vacancy and non-metallic elements, including H, B, C, F, Si, P and S, on the stability, structure and magnetic properties of monolayer SnO. In this paper, our results show that O vacancy and non-metallic atoms X doped monolayer SnO are stable at room temperature by the formation energy and molecular dynamics simulations. Meanwhile, although doped atoms X and O vacancy lead to the local structure deformation in monolayer SnO, it does not break the fourfold coordination structure. Moreover, the non-metallic elements H, B, F, Si and P is induced magnetism in monolayer SnO system and the magnetic moments are 0.73, 1.11, 0.87, 2.15 and 0.81μB, respectively. The doping of non-magnetic elements enables p-type oxides to acquire magnetism, which further expands their applications in field of spintronics.

Bi Layer Properties in the Bi–FeNi GMR-Type Structures Probed by Spectroscopic Ellipsometry

Bismuth (Bi) having a large atomic number is characterized by a strong spin–orbit coupling (SOC) and is a parent compound of many 3D topological insulators (TIs). The ultrathin Bi films are supposed to be 2D TIs possessing a nontrivial topology, which opens the possibility of developing new efficient technologies in the field of spintronics. Here we aimed at studying the dielectric function properties of ultrathin Bi/FeNi periodic structures using spectroscopic ellipsometry. The [Bi(d)–FeNi(1.8 nm)]N GMR-type structures were grown by rf sputtering deposition on Sitall-glass (TiO2) substrates. The ellipsometric angles Ψ(ω) and Δ(ω) were measured for the grown series (d = 0.6, 1.4, 2.0, and 2.5 nm, N = 16) of the multilayered film samples at room temperature for four angles of incidence of 60∘, 65∘, 70∘, and 75∘ in a wide photon energy range of 0.5–6.5 eV. The measured ellipsometric angles, Ψ(ω) and Δ(ω), were simulated in the framework of the corresponding multilayer model. The complex (pseudo)dielectric function spectra of the Bi layer were extracted. The GMR effects relevant for the studied Bi–FeNi MLF systems were estimated from the optical conductivity zero-limit (optical GMR effect). The obtained results demonstrated that the Bi layer possessed the surface metallic conductivity induced by the SOC effects, which was strongly enhanced on vanishing the semimetallic-like phase contribution on decreasing the layer thickness, indicating its nontrivial 2D topology properties.

Progress in ultrafast spintronics research

Ultrafast spintronics is one of the most promising fields for information processing technology innovation. When compared with traditional electronic devices, new spin-based devices have advantages such as low power consumption, high speed, and nonvolatility. Exploring novel physical phenomena and mechanisms relating to electronic spins significantly promotes the development of next-generation spintronic devices. In this review, we outline a sequence of advances in the fields of ultrafast magnetics and spintronics. First, a quick overview of spintronics and the discovery of ultrafast demagnetization induced by a femtosecond laser is provided. The proposed physical mechanisms and theories of ultrafast spin dynamics are then summarized, including the phenomenological three-temperature model, computations based on the time-dependent density functional theory, the Elliott-Yafet spin-flip mechanism, and the nonlocal superdiffusive spin transport model. Following that, the most recent experimental and theoretical studies on all-optical switching of ferrimagnetic and ferromagnetic metals are thoroughly reviewed. Furthermore, the discovery of hot-electron spin transport induced by ultrashort lasers as well as its influence on ultrafast magnetization dynamics, ultrafast spin transfer torque, spin injection into semiconductors, and spin accumulation and dissipation in hot-electron transport are described. The advancements in the optimization and manipulation of spintronics-based terahertz emitters are reviewed and analyzed. Finally, we discuss the current challenges in ultrafast spintronics research as well as possible future studies.

Properties of Free Charge Carriers Govern Exciton Polarization in Plasmonic Semiconductor Nanocrystals.

Interaction between a plasmon, as a collective property of charge carriers, and electronic or spin states in complex nanostructures has emerged as one of the fascinating topics that intertwines the fields of photonics, optoelectronics, and spintronics. Here, we investigate the magneto-optical properties of plasmonic InN and Cu2-xSe nanocrystals and show that the complete exciton polarization induced by cyclotron motion of free carriers is a universal phenomenon in semiconductor nanocrystals. The selective exciton polarization is governed by the angular momentum transfer from the carriers following cyclotron orbits to the excited electronic band states and can be controlled by carrier type (electrons or holes), mass, and velocity. The results of this work demonstrate the free-carrier-induced control of the states around the Fermi level and the exciton polarization in technologically important III-V nanocrystals, allowing for new ways of tailoring quantum states for spintronic and optoelectronic applications.

Picosecond optospintronic tunnel junctions

Significance Spintronic devices have become promising candidates for next-generation memory architecture. However, state-of-the-art devices, such as perpendicular magnetic tunnel junctions (MTJs), are still fundamentally constrained by a subnanosecond speed limitation, which has remained a long-lasting scientific obstacle in the ultrafast spintronics field. The highlight of our work is the demonstration of an optospintronic tunnel junction, an all-optical MTJ device which emerges as a new category of integrated photonic–spintronic memory. We demonstrate 1) laser-induced deterministic and efficient writing by an all-optical approach and electrical readout by tunnel magnetoresistance, 2) writing speed within 10 ps, demonstrated by femtosecond-resolved measurements, and 3) integration with state-of-the-art MTJ performance and a complementary metal–oxide–semiconductor-compatible fabrication progress.

Influence of Varying Tensile Stress on Domain Motion.

Magnetic domain motion has been widely studied in the fields of spintronics, nanowires, and thin films. However, there is a lack of such studies on industrial steels, especially for domain motion under the action of varying stress. Understanding domain motion under stress is helpful for the improvement of evaluation accuracy and the establishment of theoretical models of passive, nondestructive testing technology. This paper presents the influence of varying tensile stresses on the magnetic domain motion of silicon steel sheets. Magnetic domain rotation and domain wall displacement were characterized using magnetic domain images, and their motion mechanisms under elastic and plastic stresses are presented. The results show that the domain rotation under stress involves reversible and irreversible changes. The effect of material rearrangement on domain rotation and domain wall displacement after plastic deformation is discussed. Based on the motion mechanism, a threshold stress value (TSV) required for the complete disappearance of the supplementary domains in the elastic range is proposed, enabling the classification of the elastic stress ranges in which the reversible and irreversible domain rotations occur. In addition, the effect of microstructure on TSV is also discussed, and the results show that the regions far away from the grain boundary need larger stresses to complete an irreversible domain rotation. Additionally, the domain width and orientation also affect the TSV. These findings regarding the domain motion mechanism and TSV can help to explain the sequence of domain rotation under stress and modify the stress assessment under dynamic loads in electromagnetic nondestructive evaluation, especially in the magnetic memory method.

First-Principles Study on Possible Half-Metallic Ferrimagnetism in Double Perovskites Pb2XX'O6 (X = Ti, Zr, Hf, V, Nb and Ta, X' = Tc, Ru, Os and Rh).

Pb-based double perovskite compounds with chemical formula Phey have abundant physical properties in the spintronic field. Among all the features, the spin interaction of half-metallic (HM) is regarded as an important performance measure because of its high potential in spintronic devices. In this research study, we calculate density of state (DOS) to investigate possible half-metal candidates by executing structural optimization based on the method of generalized gradient approximation (GGA) and strong correlation effect (GGA + U). Furthermore, following the earlier methods by calculating and comparing energy difference of various compounds with the four initial magnetic states: ferromagnetic, ferrimagnetic, antiferromagnetic and nonmagnetic, we can determine which magnetic state is more stable. Results indicate that there are 13 possible ferrimagnetic HM candidates in these combinations, including Pb2NbTcO6, Pb2TaTcO6, Pb2TiRuO6, Pb2ZrRuO6, Pb2HfRuO6, Pb2VRuO6, Pb2NbRuO6, Pb2TadRuO6, Pb2ZrOsO6, Pb2HfOsO6, Pb2VOsO6, Pb2ZrRhO6 and Pb2HfRhO6 under GGA and GGA + U schemes. The stability of analysis by analyzing the energy gap illustrates that all 13 possible candidates are half metals and ferrimagnetic states, so our studies could provide guidelines for scientists to fabricate new double perovskites in future.

Abnormal Magnetoresistance Transport Properties of van der Waals Antiferromagnetic FeNbTe2

The emergence of two-dimensional (2D) van der Waals magnetic materials has attracted enormous attention due to their novel physical phenomena and potential application in the fields of spintronics and information storage technology. Here, we systematically study the magnetic and transport properties of a van der Waals antiferromagnetic material, FeNbTe2. The magnetic and magnetoresistance measurements verified its antiferromagnetic properties, spin glass state, and negative magnetoresistance effect at lower temperatures. In addition, the measurement results of transport also show the existence of angle-dependent anisotropic magnetoresistance in a wide temperature range and anisotropic magnetoresistance inversion in a certain temperature range.

Progress toward picosecond on-chip magnetic memory

We offer a perspective on the prospects of ultrafast spintronics and opto-magnetism as a pathway to high-performance, energy-efficient, and non-volatile embedded memory in digital integrated circuit applications. Conventional spintronic devices, such as spin-transfer-torque magnetic-resistive random-access memory (STT-MRAM) and spin–orbit torque MRAM, are promising due to their non-volatility, energy-efficiency, and high endurance. STT-MRAMs are now entering into the commercial market; however, they are limited in write speed to the nanosecond timescale. Improvement in the write speed of spintronic devices can significantly increase their usefulness as viable alternatives to the existing CMOS-based devices. In this article, we discuss recent studies that advance the field of ultrafast spintronics and opto-magnetism. An optimized ferromagnet–ferrimagnet exchange-coupled magnetic stack, which can serve as the free layer of a magnetic tunnel junction (MTJ), can be optically switched in as fast as ∼3 ps. Integration of ultrafast magnetic switching of a similar stack into an MTJ device has enabled electrical readout of the switched state using a relatively larger tunneling magnetoresistance ratio. Purely electronic ultrafast spin–orbit torque induced switching of a ferromagnet has been demonstrated using ∼6 ps long charge current pulses. We conclude our Perspective by discussing some of the challenges that remain to be addressed to accelerate ultrafast spintronics technologies toward practical implementation in high-performance digital information processing systems.

Multifunctional spintronic device based on zigzag SiC nanoribbon heterojunction via edge asymmetric dual-hydrogenation

The authors propose a method to obtain the multifunctional spintronic device by investigating the spin-resolved transport characteristics of zigzag SiC nanoribbon (zSiCNR) heterojunction via edge asymmetric dual-hydrogenation. The spin-resolved band structures show that the dual-hydrogenation on edge C or Si atoms all can change the initial metallicity of the pristine zSiCNR with the edge mono-hydrogenation to semiconductor in the presence of ferromagnetic field. The spin-resolved current-voltage characteristics of the zSiCNR heterojunction can show spin current rectification in the same rectify direction under the parallel magnetic field. The up-spin rectification ratio of our junction can be close to 10 13 at −0.5 V, which is much larger than rectification ratios of the previous junctions induced by the anti-parallel magnetic field. The zSiCNR heterojunction also exhibits a perfect spin filtering behavior with 100% spin filtering efficiency in both positive and negative bias regions under the anti-parallel magnetic field. More interestingly, the magnetoresistance is achieved by manipulating the external magnetic field in our zSiCNR heterojunction with the giant magnetoresistance ratio 5000% at 0.5 V. Therefore, the zSiCNR heterojunction via edge asymmetric dual-hydrogenation can be designed into the multifunctional spintronic devices, which has broad application prospects in the field of future spintronics. • Zigzag silicon carbon nanoribbon has potential in spin devices. • Giant spin current rectification is obtained in the presence of a ferromagnetic field. • Maximum spin current rectification ratios is closing to 10 13 . • Perfect spin filtering and magnetoresistance behaviors are also obtained.

A Unique Mechanochemical Redox Reaction Yielding Nanostructured Double Perovskite Sr2FeMoO6 With an Extraordinarily High Degree of Anti-Site Disorder.

Strontium ferromolybdate, Sr2FeMoO6, is an important member of the family of double perovskites with the possible technological applications in the field of spintronics and solid oxide fuel cells. Its preparation via a multi-step ceramic route or various wet chemistry-based routes is notoriously difficult. The present work demonstrates that Sr2FeMoO6 can be mechanosynthesized at ambient temperature in air directly from its precursors (SrO, α-Fe, MoO3) in the form of nanostructured powders, without the need for solvents and/or calcination under controlled oxygen fugacity. The mechanically induced evolution of the Sr2FeMoO6 phase and the far-from-equilibrium structural state of the reaction product are systematically monitored with XRD and a variety of spectroscopic techniques including Raman spectroscopy, 57Fe Mössbauer spectroscopy, and X-ray photoelectron spectroscopy. The unique extensive oxidation of iron species (Fe0 → Fe3+) with simultaneous reduction of Mo cations (Mo6+ → Mo5+), occuring during the mechanosynthesis of Sr2FeMoO6, is attributed to the mechanically triggered formation of tiny metallic iron nanoparticles in superparamagnetic state with a large reaction surface and a high oxidation affinity, whose steady presence in the reaction mixture of the milled educts initiates/promotes the swift redox reaction. High-resolution transmission electron microscopy observations reveal that the mechanosynthesized Sr2FeMoO6, even after its moderate thermal treatment at 923 K for 30 min in air, exhibits the nanostructured nature with the average particle size of 21(4) nm. At the short-range scale, the nanostructure of the as-prepared Sr2FeMoO6 is characterized by both, the strongly distorted geometry of the constituent FeO6 octahedra and the extraordinarily high degree of anti-site disorder. The degree of anti-site disorder ASD = 0.5, derived independently from the present experimental XRD, Mössbauer, and SQUID magnetization data, corresponds to the completely random distribution of Fe3+ and Mo5+ cations over the sites of octahedral coordination provided by the double perovskite structure. Moreover, the fully anti-site disordered Sr2FeMoO6 nanoparticles exhibit superparamagnetism with the blocking temperature T B = 240 K and the deteriorated effective magnetic moment μ = 0.055 μ B per formula unit.

Electronic, magnetic, and structural properties of CrMnSb0.5Si0.5

Half-metallic Heusler compounds are among the most actively studied materials for applications in spin-based devices. Largely, this is due to their higher Curie temperature compared with the other half-metallic compounds, and relative ease of fabrication. Here we theoretically study one such Heusler alloy CrMnSb0.5Si0.5. In particular, we demonstrate a potential stability of this compound by estimating its formation energy, its half-metallic electronic structure (stable under a considered range of biaxial strain), and ferrimagnetic alignment. The calculated Curie temperature of this material is 787 K, much higher than room temperature. At the same time, we have shown that in thin-film geometry the spin-polarization of this material is strongly reduced due to the emergence of surface states in the minority-spin energy gap. In addition, one of the considered termination surfaces is thermodynamically unstable, while the other is stable. The presented results may be useful for researchers working on practical applications in the field of spintronics.

Stabilization of nanoscale iron films by self-terminated electrodeposition in sulfate electrolyte

Iron and iron oxide nanostructures are of broad interest for numerous applications, such as in the fields of magnetic data storage, spintronics, biosensing and catalysis. In all of these cases, defined deposition on nanometer scale is essential for functionality. For conventional electrodeposition of transition metals, precise thickness control and layer stability at the nanoscale are difficult due to dissolution tendencies in acidic electrolytes after the voltage is switched off. In contrast to previous studies that focused on self-termination of Ni and Ni-based alloys, we investigate the thickness control of nanoscale iron oxide/iron layers using self-terminated electrodeposition from sulfate electrolytes. Electrochemical quartz crystal microbalance measurements show that self-terminated thickness can be controlled by both deposition potential and iron ion concentration. Comparison of experimental results with model calculations based on diffusion theory reveal two different growth modes for self-termination. At low iron ion concentration, self-termination of iron proceeds via the formation of an ultrathin iron hydroxide layer. At larger iron ion concentration, precipitation of bulk Fe(OH)2 dominates the film growth and self-termination is shifted to more negative potentials. All self-terminated layers exhibit enhanced stability in the electrolyte after the voltage is switched off compared to those deposited in the conventional deposition regime. With in situ Rutherford backscattering spectrometry measurements, we can follow the self-terminating deposition and the stability after voltage switch-off for longer times online. Surface analytical and morphological analyses show that the self-terminated layers exhibit a higher iron oxide/iron ratio and are smoother than layers obtained by conventional electrodeposition.

Experimental observation of transition from type I to type II ultrafast demagnetization dynamics in chemically disordered Fe60Al40 thin film, driven by laser fluence

Understanding of the laser-induced ultrafast demagnetization dynamics is one of the most challenging and hot topics in magnetism research due to its potential applications in magnetic storage devices and the field of spintronics. Recently, a laser-induced switching of ferromagnetism, driven by a disorder–order transition on FeAl thin films, has been experimentally demonstrated. The switching of ferromagnetic ordering by ultrafast laser pulses in FeAl thin films may open new possible applications of this material such as magnetic data storage and manipulation. Since the speed of the magnetic switching of magnetic states in thin films is one of the critical parameters for these applications, here we used time resolved magneto-optical Kerr measurements to investigate the demagnetization dynamics of Fe60Al40 thin films at room temperature. We have for the first time observed a clear transition from one-step dynamics (type I) to two-step (type II) dynamics in the same material by increasing pump laser fluence. This experimental observation may give a strong confirmation that the ultrafast demagnetization process can be treated as a thermal process and is driven by the difference between temperatures of the electron and spin systems.

Tunnel magnetodielectric effect: Theory and experiment

The recently discovered tunnel magnetodielectric (TMD) effect—the magnetic field-induced increase in the dielectric permittivity (ε′) of nanogranular composites caused by the spin-dependent quantum mechanical charge tunneling—is of interest for both the scientific value that combines the fields of magnetoelectric and spintronics and multifunctional device applications. However, little is known about how large the maximum dielectric change Δε′/ε′ can achieve and why the Δε′/ε′ variations obey the dependence of square of normalized magnetization (m2), which are critically important for searching and designing materials with higher Δε′/ε′. Here, we perform approximate theoretical derivation and reveal that the maximum Δε′/ε′ can be estimated using intrinsic tunneling spin polarization (PT) and extrinsic normalized magnetization (m), that is, Δε′/ε′ = 2PT2m2. This formulation allows predicting over 200% of theoretical limit for m = 1 and accounts for the observed m2 dependence of Δε′/ε′ for a given PT. We experimentally demonstrate that x-dependence of Δε′/ε′ in (CoxFe100−x)–MgF2 films is phenomenologically consistent with this formulation. This work is pivotal to the design of ultra-highly tunable magnetoelectric applications of the TMD effect at room temperature.