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In chemistry and biochemistry, chirality represents the structural asymmetry characterized by nonsuperimposable mirror images for a material such as DNA. In physics, however, chirality commonly refers to the spin–momentum locking of a particle or quasiparticle in the momentum space. While seemingly disconnected, structural chirality in molecules and crystals can drive electronic chirality through orbital–momentum locking; that is, chirality can be transferred from the atomic geometry to electronic orbitals. Electronic chirality provides an insightful understanding of chirality-induced spin selectivity, in which electrons exhibit salient spin polarization after going through a chiral material, and electrical magnetochiral anisotropy, which is characterized by diode-like transport. It further gives rise to new phenomena, such as anomalous circularly polarized light emission, in which the light handedness relies on the emission direction. These chirality-driven effects will generate broad impacts for fundamental science and technology applications in spintronics, optoelectronics, and biochemistry. [ABSTRACT FROM AUTHOR]

The properties of a superconducting spin valve based on Fe1/Fe2/Pb prepared on a PMN-PT piezoelectric substrate ([Pb(Mg1/3Nb2/3)O3]0.7-[PbTiO3]0.3) in external magnetic and electric fields were studied. A shift in superconducting transition temperature more than 200 mK was observed when the mutual direction of the magnetizations of the ferromagnetic layers changed from antiparallel to perpendicular orientations in an external magnetic field. The possibility of realizing the full effect of a superconducting spin valve was demonstrated. It was established that the shift in superconducting transition temperature increased with an increase in the value of the applied electric field to the PMN-PT piezoelectric substrate. [ABSTRACT FROM AUTHOR]

Today’s semiconductor devices use the charges of electrons and holes for tasks like light emission and signal processing. Semiconductor spintronics, a newer field, aims to exploit the spin of charge carriers to advance technologies like magnetic lasers, sensors, and transistors. Spintronics could enable the creation of memory, sensing, and logic devices with capabilities that charge-based devices can't match. This work explores the progress made with spintronic materials and devices, their current uses, and what the future might hold. A key feature of emerging spintronic logic devices is their ability to generate highly spin-polarized currents in two- and three-terminal tunnel junctions, which can lead to devices that consume much less power than traditional charge-based ones. Recent advancements in material engineering give hope for the rapid development and deployment of these new spintronic technologies.

Spin valves with a synthetic antiferromagnet were fabricated via magnetron sputtering. It was shown that the fabricated spin valve layers had a perfect microstructure and smooth interfaces, and therefore, an RKKY interaction dominated in the coupling of the ferromagnetic layers separated by a copper spacer. Rhombus-shaped micro-objects were fabricated from a single spin valve film. The thermomagnetic treatment procedure was found to form unidirectional anisotropy in the micro-object such that the values of the exchange bias fields in the rhombus' nonparallel sides were opposite in sign. For the CoFeNi/Ru/CoFeNi synthetic antiferromagnet, we determined the differences between the ferromagnetic layer thicknesses at which the thermomagnetic treatment formed the same exchange bias all over each rhombus' side. We also fabricated a sensor element in which each side of the rhombus was the shoulder of a Wheatstone bridge. After the thermomagnetic treatment procedure, each shoulder worked as an active magnetosensitive element, enabling the device to operate as a full Wheatstone bridge. The sensor output exhibited a step shape, high sensitivity to field changes, and significant magnetic hysteresis. Such characteristics are suitable for switching devices. [ABSTRACT FROM AUTHOR]

[Display omitted] In recent years, enormous efforts have been made to identify and manipulate the exotic electrical and magnetic properties at a two-dimensional (2D) limit of various exciting materials. The spin–orbit coupling (SOC) in 2D van der Waals (vdW) heterostructures opens a fascinating and versatile platform to implement the intriguing quantum-engineered spintronic devices for practical applications. This review comprehensively outlines the modern-era progress of investigating the inherent magnetism of atomically thin 2D materials. Firstly, in this review, the most recent developments of synthesis, characterizations, functionalities, and spin textures in 2D magnetic materials are summarized in detail. Secondly, we conferred the well-known phenomena related to the proximity effect, spin–orbit torque (SOT), spin valve magnetic tunnel junction (MTJ), spin field effect transistor (FET) and magneto memristive-based applications. In addition, we also explored the possible interplay between 2D magnetic materials and associated band topology for spin caloritronics. Finally, we provided our perspective on the recent and upcoming challenges and goals of this promising research area, which leads the 2D magnetic materials to the modern era of energy-efficient quantum computing. [ABSTRACT FROM AUTHOR]

The paper proposes a model of an electromagnetic radiation sensor that uses the precession of the magnetization vector in a ferromagnet (ferromagnetic resonance) as a result of absorbing the energy of an incident electromagnetic wave, the generation of a spin current as a result of this precession, the generation of a spin-polarized current as a result of the passage of a spin current in a non-magnetic metal, and a change in the direction of magnetization of a ferromagnetic layer with a low coercive force (free layer) due to the passage of a spin-polarized current. Then the radiation will be detected by its effect on the electrical resistance of the entire structure, which depends on the mutual directions (parallel or antiparallel) of magnetization of the free and fixed (with a large coercive force) ferromagnetic layers (phenomenon of giant magnetic resistance). The dependence of the spin-polarized current in the device on the frequency and amplitude of the incident electromagnetic wave with linear polarization was calculated. A method of calculating the range of amplitude and frequency values of radiation that can be detected by the sensor has been developed. The parameters of this model are the detection time and the number of spin gates in one sensor. Calculations are given for a ferromagnetic layer made of permalloy and for spin valves with four different critical current values that determine the process of remagnetization of the free layer: 20, 50, 100, and 200 microamps.

How to control the charge and spin in nanodevices is an important topic in spintronics. In this letter, we theoretically propose a spin diode and spin valve (SV) device controlled by all-electrical means, which is composed of a quantum dot (QD) coupled to a pair of nonmagnetic electrodes. When both electric charge bias and spin bias exist within the device, the I – V curves of this device exhibit an asymmetric distribution, and this asymmetry can be manipulated by the gate voltage. More interestingly, if we apply an external magnetic field on the QD, we can observe significant high- and low-resistance state switching with respect to the magnetic field, which can function as a SV device. This device scheme can be compatible with current technologies and has potential applications in spintronics or quantum processing. [ABSTRACT FROM AUTHOR]

We have theoretically studied the transport properties of the SIsN S O F structure consisting of thick (S) and thin (s) films of superconductor, an insulator layer (I), a thin film of normal metal with spin–orbit interaction (SOI) (N S O ), and a monodomain ferromagnetic layer (F). The interplay between superconductivity, ferromagnetism, and spin–orbit interaction allows the critical current of this Josephson junction to be smoothly varied over a wide range by rotating the magnetization direction in the single F-layer. We have studied the amplitude of the spin valve effect and found the optimal ranges of parameters. [ABSTRACT FROM AUTHOR]

We have studied the influence of the piezoelectric properties of the PMN-PT substrate ([Pb(Mg1/3Nb2/3)O3]1-x – [PbTiO3]x where x = 0.29 − 0.31) on the properties of the superconducting spin valve Fe/Al/Co/Pb exposed to electric and magnetic fields. According to the research results, with an increase in the applied electric field to the PMN-PT substrate, it is possible to register an increase in the shift of the superconducting transition temperature of the superconducting spin valve Fe/Al/Co/Pb. The maximum shift was 36 mK when an electric field of 1 kV/cm was applied, which was half of the superconducting transition width. The shift of the superconducting transition temperature equal to 255 mK in a magnetic field was recorded, and thus the possibility of a full superconducting spin valve effect was shown. [ABSTRACT FROM AUTHOR]

Spin valves with a synthetic antiferromagnet were fabricated via magnetron sputtering. It was shown that the fabricated spin valve layers had a perfect microstructure and smooth interfaces, and therefore, an RKKY interaction dominated in the coupling of the ferromagnetic layers separated by a copper spacer. Rhombus-shaped micro-objects were fabricated from a single spin valve film. The thermomagnetic treatment procedure was found to form unidirectional anisotropy in the micro-object such that the values of the exchange bias fields in the rhombus’ nonparallel sides were opposite in sign. For the CoFeNi/Ru/CoFeNi synthetic antiferromagnet, we determined the differences between the ferromagnetic layer thicknesses at which the thermomagnetic treatment formed the same exchange bias all over each rhombus’ side. We also fabricated a sensor element in which each side of the rhombus was the shoulder of a Wheatstone bridge. After the thermomagnetic treatment procedure, each shoulder worked as an active magnetosensitive element, enabling the device to operate as a full Wheatstone bridge. The sensor output exhibited a step shape, high sensitivity to field changes, and significant magnetic hysteresis. Such characteristics are suitable for switching devices.

Magnetic tunnel junctions (MTJs), a prominent type of spintronic device based on the spin valve effect, have facilitated the development of numerous spintronic applications. The technical appeal for the next‐generation MTJ devices has been proposed in two directions: improving device performance by utilizing advanced two‐dimensional (2D) ferromagnetic materials or extending device functionalities by exploring the gate‐tunable magnetic properties of ferromagnets. Based on the recent development of 2D magnets with the ease of external stimuli, such as electric field, due to their reduced dimensions, reliable prospects for gate‐tunable MTJ devices can be achieved, shedding light on the great potential of next‐generation MTJs with multiple functionalities for various application environments. While the electrical gate‐tunable MTJ device is highly desirable for practical spintronic devices, it has not yet been demonstrated. Here, we demonstrate the experimental realization of a spin valve device by combining a vertical Fe3GeTe2/h‐BN/Fe3GeTe2 MTJ with an electrolyte gate. The magnetoresistance ratio (MR ratio) of 36% for the intrinsic MTJ confirms the good performance of the device. By electrolyte gating, the tunneling MR ratio of Fe3GeTe2/h‐BN/Fe3GeTe2 MTJ can be elevated 2.5 times, from 26% to 65%. Importantly, the magnetic fields at which the magnetoresistance switches for the MTJ can be modulated by electrical gating, providing a promising method to control the magnetization configuration of the MTJ. Our work demonstrates a gate‐tunable MTJ device toward the possibility for gate‐controlled spintronic devices, paving the way for performing 2D magnetism manipulations and exploring innovative spintronic applications. [ABSTRACT FROM AUTHOR]

Spin valves containing a Dy layer have been formed on an elastic polyimide film by magnetron sputtering. The field dependences of the magnetoresistance of samples subjected to different tensile deformations have been measured. The character of the variations of the magnetoresistive properties of a spin valve subjected to tensile deformation is shown to depend on the thickness of the dysprosium layer. In particular, the thickness of the dysprosium layer affects the maximum relative elongation at which the magnetoresistance of spin valves remains unchanged. [ABSTRACT FROM AUTHOR]

Abstract Magnetic tunnel junctions (MTJs), a prominent type of spintronic device based on the spin valve effect, have facilitated the development of numerous spintronic applications. The technical appeal for the next‐generation MTJ devices has been proposed in two directions: improving device performance by utilizing advanced two‐dimensional (2D) ferromagnetic materials or extending device functionalities by exploring the gate‐tunable magnetic properties of ferromagnets. Based on the recent development of 2D magnets with the ease of external stimuli, such as electric field, due to their reduced dimensions, reliable prospects for gate‐tunable MTJ devices can be achieved, shedding light on the great potential of next‐generation MTJs with multiple functionalities for various application environments. While the electrical gate‐tunable MTJ device is highly desirable for practical spintronic devices, it has not yet been demonstrated. Here, we demonstrate the experimental realization of a spin valve device by combining a vertical Fe3GeTe2/h‐BN/Fe3GeTe2 MTJ with an electrolyte gate. The magnetoresistance ratio (MR ratio) of 36% for the intrinsic MTJ confirms the good performance of the device. By electrolyte gating, the tunneling MR ratio of Fe3GeTe2/h‐BN/Fe3GeTe2 MTJ can be elevated 2.5 times, from 26% to 65%. Importantly, the magnetic fields at which the magnetoresistance switches for the MTJ can be modulated by electrical gating, providing a promising method to control the magnetization configuration of the MTJ. Our work demonstrates a gate‐tunable MTJ device toward the possibility for gate‐controlled spintronic devices, paving the way for performing 2D magnetism manipulations and exploring innovative spintronic applications.

The utilisation of quantum properties can largely impact how technological devices work. Up to date, the acquired knowledge of the quantum nature of several systems inspired the proposal of several novel technologies such as quantum sensing, quantum simulation and quantum computing. Single Molecule Magnets (SMMs) represent a class of quantum objects with promising properties to be exploited in quantum technologies. As of today, SMMs have been shown to possess bewildering quantum effects such as Quantum Tunnelling of the Magnetisation (QTM), quantisation of the energy manifold, coherence, spin parity effects and entanglement, among others. Furthermore, they have been successfully integrated into hybrid single-molecule spintronic devices, such as spin transistors and spin valves, hence, propitiating extensive investigation of technological applications. In this Review Article, some key quantum aspects, which make SMMs promising systems for technological proposals, are revised. Moreover, single-molecule devices, in which SMMs have been integrated in hybrid devices, as well as the technological applications such as quantum sensing, quantum simulation and quantum computing are described.

The utilisation of quantum properties can largely impact how technological devices work. Up to date, the acquired knowledge of the quantum nature of several systems inspired the proposal of several novel technologies such as quantum sensing, quantum simulation and quantum computing. Single Molecule Magnets (SMMs) represent a class of quantum objects with promising properties to be exploited in quantum technologies. As of today, SMMs have been shown to possess bewildering quantum effects such as Quantum Tunnelling of the Magnetisation (QTM), quantisation of the energy manifold, coherence, spin parity effects and entanglement, among others. Furthermore, they have been successfully integrated into hybrid single-molecule spintronic devices, such as spin transistors and spin valves, hence, propitiating extensive investigation of technological applications. In this Review Article, some key quantum aspects, which make SMMs promising systems for technological proposals, are revised. Moreover, single-molecule devices, in which SMMs have been integrated in hybrid devices, as well as the technological applications such as quantum sensing, quantum simulation and quantum computing are described.

Spin valves with a CoFe/Dy/CoFe composition in the lower part of their structure have been manufactured by magnetron sputtering. The effect of prolonged storage and temperature on the structure and magnetotransport properties of spin valves has been studied. The change in the compensation temperature was used as an indicator of the intensity of diffusion processes in the exchange-coupled CoFe/Dy/CoFe structure. It has been revealed that diffusion induced changes in the magnetotransport properties become smaller with a decrease in the dysprosium layer thickness. It has been shown that the nanostructure still contains pure dysprosium, the atoms of which do not participate in the sperimagnetic ordering of the Dy–Co–Fe interface, even at a small nominal thickness (4 nm) of the dysprosium layer 3 months after sputtering. [ABSTRACT FROM AUTHOR]

The effect of nanoparticles (NPs) on microwave magnetoresistance in MgO/CoFeB(free)/Ta/CoFeB(fixed)/MgO)/Ta platform and the effect of individual NP on free CoFeB ferromagnetic layer magnetization have experimentally been revealed and analyzed. The area of the platform where magnetization is inverted under scattering field of NPs has been observed. Micromagnetic modeling of dipole magnetic interaction confirms the existence of such areas in “NP-platform” system. The increase in critical field of the platform and the change of resistance under scattering field on NPs have experimentally been revealed. [ABSTRACT FROM AUTHOR]

We have theoretically studied the transport properties of the SIsNSOF structure consisting of thick (S) and thin (s) films of superconductor, an insulator layer (I), a thin film of normal metal with spin–orbit interaction (SOI) (NSO), and a monodomain ferromagnetic layer (F). The interplay between superconductivity, ferromagnetism, and spin–orbit interaction allows the critical current of this Josephson junction to be smoothly varied over a wide range by rotating the magnetization direction in the single F-layer. We have studied the amplitude of the spin valve effect and found the optimal ranges of parameters.

This work is a study of the formation processes and the effect of related process parameters of multilayer nanosystems and devices for spintronics. The model system is a superconducting spin valve, which is a multilayer structure consisting of ferromagnetic cobalt nanolayers separated by niobium superconductor nanolayers. The aim was to study the influence of the main technological parameters including temperature, concentration and spatial distribution of deposited atoms over the nanosystem surface on the atomic structure and morphology of the nanosystem. The studies were carried out using the molecular dynamics method using the many-particle potential of the modified embedded-atom method. In the calculation process the temperature was controlled using the Nose–Hoover thermostat. The simulation of the atomic nanolayer formation was performed by alternating the directional deposition of different composition layers under high vacuum and stationary temperature conditions. The structure and thickness of the formed nanolayers and the distribution of elements at their interfaces were studied. The alternating layers of the formed nanosystem and their interfaces are shown to have significantly different atomic structures depending on the main parameters of the deposition process.

The key to achieving high-quality and practical van der Waals heterostructure devices made from various two-dimensional (2D) materials lies in the efficient control over clean and flexible interfaces. Inspired by the “movable-type printing”, one of the four great inventions of ancient China, we demonstrate the “movable-type” transfer and stacking of 2D materials, which utilizes prefabricated polyvinyl alcohol (PVA) film to engineer the interfacial adhesion to 2D materials, and provides a flexible, efficient and batchable transfer scheme for 2D materials. The experiments also verify the “movable-type” transfer can preciously control the position and orientation of 2D materials, which meets the burgeoning requirements such as the preparation of twisted graphene and other heterostructures. Importantly, water-solubility of PVA film ensures an ideal interface of the materials without introducing contamination. We illustrate the superiority of this method with a WSe2 vertical spin valve device, whose performance verifies the applicability and advantages of such a method for spintronics. Our PVA-assisted “movable-type” transfer process may promote the development of high-performance 2D-material-based devices.

Magnetic sensor with spin valve-GMR technology with medium dynamic range is designed for a diversity of applications, including linear and rotary position measurements, proximity switches, and current sensors. For this, the sensing layer (SL) of the spin valve stack was modified by a soft pinning layer (SPL) through an exchange bias field created by an antiferromagnetic layer which has a lower blocking temperature than the one that is kept adjacent to the pinned layer. Numerical simulation was carried out to control the bias field by keeping a non-magnetic Ru spacer layer between the SPL and SL layers and the results were experimentally verified. The magnetic sensor was fabricated with linear operating field range of the order ±100 Oe having a sensitivity of the order of 0.1 m V V -1 Oe -1 near zero field. The thermal performance confirms that the device can be operated in the temperature range of -40 ∘ C to 125 ∘ C and it has a thermal coefficient of voltage around 15 µ V V -1∘ C -1 ., (© 2024 IOP Publishing Ltd.)

Layered spin-valve structures are basic elements of micromagnetic devices. Small dimensions, CMOS compatibility, good scalability, and a diversity of operation conditions make spin-valve structures a universal component of modern microelectronics. The aim of this review is to analyze, systematize, and generalize the fundamentals of the operation, experimental data, and application of spin valves. Hard disk drives, magnetoresistive random access memory, spin-transfer nano-oscillators, magnetic biosensors, and various computing systems operating on the basis of stochastic and deterministic logic are reviewed. The key theoretical studies on the giant magnetoresistance and spin transport are considered. Data on different types of hard disk reading heads are systematized and their architecture and parameters are compared. It is shown how modern investigations of nanomagnetic phenomena accelerates the recording density growth. The state of research on the magnetoresistive random access memory is analyzed. The issues of energy efficiency and enhancement of the degree of integration in these devices are discussed. The latest progress in the materials, geometry, and properties of spin-transfer nano-oscillators and the problems and prospects of this technology are considered. The theoretical and experimental studies are analyzed in which the spin-valve structures perform Boolean and non-Boolean logic operations. It is demonstrated how the stochastic nature of the unstable switching of spin valves is used in nonconventional computing systems, specifically, the neuromorphic or Bayesian networks. The principles of operation of spin valves as magnetic biosensors and the advantages of their application are discussed. [ABSTRACT FROM AUTHOR]

Exchange-coupled spin valves based on ferromagnetic alloys CoFeNi and antiferromagnetic alloy FeMn are obtained on flexible polyimide substrates by magnetron sputtering. The magnetoresistive properties of films and microstrips of spin valves are measured at various degrees of bending deformation of the sample. The behavior of the dependence of the deformation sensitivity of the spin valve on the interaction between the magnetic layers and on the arrangement of the anisotropy axes with respect to the deformation vector is characterized. It is found that the deformation sensitivity decreases with an increase in the interval between the fields of magnetization reversal of the free and fixed layers in the spin valve. [ABSTRACT FROM AUTHOR]

Exchange-biased nanostructures of the "spin valve" type, which include an additional layer of the rare-earth metal dysprosium, are made by magnetron sputtering. Temperature variations in the magnetotransport properties of the spin valves are used as an indicator of change in the magnetic state of the dysprosium nanolayer. Information on the formation of unidirectional magnetic anisotropy at the CoFe/Dy interface upon the transition through Néel temperature of dysprosium is obtained. It is shown that the antiferromagnetic phase in the polycrystalline dysprosium layer has noncollinear magnetic ordering. The temperature dependence of the angle between the directions of the magnetic moments at the dysprosium-layer boundaries is determined. The change in this angle observed in the entire temperature region of the existence of helicoidal ordering in dysprosium reflects the change in the period of the magnetic helicoid in dysprosium with temperature. Thus, a new method for studying chiral magnetics is proposed, in which the indicator of the helicoidal magnetic state is a spin valve possessing giant magnetoresistance, containing a layer of the helimagnet under investigation. [ABSTRACT FROM AUTHOR]

A Ti2NiAl inverse Heusler alloy based current-perpendicular-to-plane (CPP) spin valve (SV) with various kinds of atomic terminated interfaces has been designed to explore the potential application of Heusler alloys in spintronics devices. By performing first principles calculations combined with the nonequilibrium Green’s function, it is revealed that spin magnetic moments of interfacial atoms suffer a decrease, and the electronic structure shows that the TiNiB-terminated structure possesses the largest interface spin polarization of ≈55%. Our study on spin-transport properties indicates that the total transmission coefficient at the Fermi level mainly comes from the contribution from the spin up electrons, which are regarded as the majority of the spin electrons. When the two electrodes of the CPP-SV device are in parallel magnetization configuration, the interface containing Ti and Ni atoms possesses a higher spin up transmission coefficient than the interface containing Ti and Al atoms. The device with the TiNiB-terminated interface possesses the largest magnetoresistance ratio of 3.28 × 105, and it has great application potential in spintronics devices.

We present a study of magnetic structures with controllable effective exchange energy for Josephson switches and memory applications. As a basis for a weak link we propose to use a periodic structure composed of ferromagnetic (F) layers spaced by thin superconductors (s). Our calculations based on the Usadel equations show that switching from parallel (P) to antiparallel (AP) alignment of neighboring F layers can lead to a significant enhancement of the critical current through the junction. To control the magnetic alignment we propose to use a periodic system whose unit cell is a pseudo spin valve of structure F1/s/F2/s where F1 and F2 are two magnetic layers having different coercive fields. In order to check the feasibility of controllable switching between AP and P states through the whole periodic structure, we prepared a superlattice [Co(1.5 nm)/Nb(8 nm)/Co(2.5 nm)/Nb(8 nm)]6 between two superconducting layers of Nb(25 nm). Neutron scattering and magnetometry data showed that parallel and antiparallel alignment can be controlled with a magnetic field of only several tens of Oersted.

The dependence of the Neel temperature on the thickness of the dysprosium layer has been studied. It is shown that the temperature range within which the paramagnetic–antiferromagnetic phase transition takes place depends on the microstructure and thickness of the dysprosium layer. Spin valves based on a CoFe alloy with dysprosium as an antiferromagnetic layer are manufactured via magnetron sputtering. It is shown that unidirectional anisotropy forms in the CoFe/Dy interface. The direction of the exchange bias field depends on the direction of the magnetic moment of the CoFe layer in the formation of exchange coupling. [ABSTRACT FROM AUTHOR]

The pursuit of van der Waals (vdW) heterostructures with high Curie temperature and strong perpendicular magnetic anisotropy (PMA) is vital to the advancement of next generation spintronic devices. First-principles calculations are used to study the electronic structures and magnetic characteristics of GaN/VS 2 vdW heterostructure under biaxial strain and electrostatic doping. Our findings show that a ferromagnetic ground state with a remarkable Curie temperature (477 K), much above room temperature, exists in GaN/VS 2 vdW heterostructure and 100% spin polarization efficiency. Additionally, GaN/VS 2 vdW heterostructure still maintains PMA under biaxial strain, which is indispensable for high-density information storage. We further explore the electron, magnetic, and transport properties of VS 2 /GaN/VS 2 vdW sandwich heterostructure, where the magnetoresistivity can reach as high as 40%. Our research indicates that the heterostructure constructed by combining the ferromagnet VS 2 and the non-magnetic semiconductor GaN is a promising material for vdW spin valve devices at room temperature., (© 2024 IOP Publishing Ltd.)

π-Conjugated semiconductors, primarily composed of elements with low atomic number, are regarded as promising spin-transport materials due to the weak spin–orbit coupling interaction and hence long spin relaxation time. Moreover, a large number of additional functions of organic semiconductors (OSCs), such as the abundant photo-electric properties, flexibility, and tailorability, endow the organic spintronic devices more unique properties and functionalities. Particularly, the integration of the photo-electric functionality and excellent spin transport property of OSCs in a single spintronic device has even shown great potential for the realization of spin manipulation in OSCs. In this review, the application of OSCs in spintronic study will be succinctly discussed. As the most important and extensive application, the long-distance spin transport property of OSCs will be discussed first. Subsequently, several multifunctional spintronic devices based on OSCs will be summarized. After that, the organic-based magnets used for the electrodes of spintronic devices will be introduced. Finally, according to the latest progress, spin manipulation in OSCs via novel spintronic devices together with other prospects and challenges will be outlined.

We have studied superconducting properties of spin-valve thin-layer heterostructures CoOx/F1/Cu/F2/Cu/Pb in which the ferromagnetic F1 layer was made of Permalloy while for the F2 layer we have taken a specially prepared film of the Heusler alloy Co2Cr1−xFexAl with a small degree of spin polarization of the conduction band. The heterostructures demonstrate a significant superconducting spin-valve effect, i.e., a complete switching on and off of the superconducting current flowing through the system by manipulating the mutual orientations of the magnetization of the F1 and F2 layers. The magnitude of the effect is doubled in comparison with the previously studied analogous multilayers with the F2 layer made of the strong ferromagnet Fe. Theoretical analysis shows that a drastic enhancement of the switching effect is due to a smaller exchange field in the heterostructure coming from the Heusler film as compared to Fe. This enables to approach an almost ideal theoretical magnitude of the switching in the Heusler-based multilayer with a F2 layer thickness of ca. 1 nm.

Spin valves with holmium layers and three-layer structures metal/Ho/metal were prepared by magnetron sputtering. A holmium layer in the spin valves is polycrystalline with weak axial <002> texture. The structural coherence length along the hexagonal c-axis is approximately 2/5 of the total thickness of the holmium layer. Field dependences of the spin valves magnetoresistance were measured at different temperatures. Correlation was revealed between magnetic state in holmium layer and the shape of magnetoresistive curve. Deviation of magnetic moments of the reference layer and the adjacent part of holmium from the applied magnetic field was investigated. The field induced mobility of the magnetic helicoid in holmium layers was revealed. Image 1 • Neel temperature of Ho layer depends on the thickness and microstructure perfection. • Antiferromagnetic Ho layer carries out exchange bias in the adjacent ferromagnetic. • Spin valve magnetoresistance correlates with the magnetic state in Ho layer. • Period of the magnetic helicoid in Ho layer varies with temperature. • The magnetic helicoid in Ho layer is rotated around c-axis by magnetic field. [ABSTRACT FROM AUTHOR]

In spin valve sensors, the bias point caused by the interlayer coupling between the pinned layer and the free layer is a crucial issue encountered in the design process, which degrades the responsivity and the weak-field detection feature. In tackling this issue, we present the magnetic bias technique for efficient control of the bias point of the pinned spin valve (PSV). Specifically, the magnetic field that creates a shift of the bias point is generated by a coil being wrapped around the PSV devices. The PSV multilayer structure, Ta(5 nm)/NiFe(3 nm)/CoFe(4.5 nm)/Cu(1.5 nm)/CoFe(2.4 nm)/IrMn(10 nm)/Ta(5 nm), was fabricated using DC magnetron sputtering deposition. The PSV devices patterned by using a simple lift-off technique have a dimension of 1.5 µm × 200 µm. The bias magnetic field was tuned between ± 5 mT by changing an external DC current. Our experimental results indicate that the bias point can be efficiently controlled via a simple adjustment of the current in the bias coil. Consequently, the device responsivity was remarkably enhanced by a factor of 6.75, from 0.8 V/T to 5.4 V/T, leading to a decrease of the detectivity (field noise) from 366 nT/√Hz@1 Hz to 108 nT/√Hz@1 Hz. Additionally, the field noise was further suppressed by a factor of 5 from 363 nT/√Hz@1 Hz to 72 nT/√Hz@1 Hz by applying the AC-driven mode in the half-bridge PSV. The simplicity of our proposed technique makes it particularly pertinent to PSV sensor designs for low-field applications. [ABSTRACT FROM AUTHOR]

A method of universal thermomagnetic treatment forming a pairwise opposite exchange bias in spin valves, which are sensor elements of a Wheatstone bridge, has been developed. The method is based on the formation of two magnetic phases in a spin valve upon the transition of a synthetic antiferromagnet into a spin-flop state. Thermomagnetic treatment in a two-phase state leads to the formation of a pairwise mutually opposite exchange bias in different elements of a Wheatstone bridge. The direction of a formed exchange bias is governed by the uniaxial anisotropy of every element. [ABSTRACT FROM AUTHOR]

Spin valves based on materials in which the spin-flip is suppressed by the spatial separation of charge carriers, while maintaining electric neutrality in the valve volume, are considered. The possibility of using these valves as electric batteries is discussed. Regulating the potential difference on the valve, one can expect the effects of incommensurability of the type of "devil's staircase" associated with the Coulomb interaction and redistribution of electrons occurring while the battery is charged and discharged. The effects of the emergence and vanishing of spontaneous spin polarization of conduction electrons with a change in the Fermi level in the valve are predicted. Such spin valves can also be used in implementing spintronic memory cells, supercapacitors, and similar devices. [ABSTRACT FROM AUTHOR]

Spin valves comprising a synthetic antiferromagnet and a CoFe/Dy/CoFe structure in the pinned layer were prepared by magnetron sputtering. It is shown that the Dy layer is characterized by crystallites, the [0002] direction of which is perpendicular to the film plane; a part of nanostructure, in which the spin-dependent electron scattering occurs, is characterized by smooth interfaces. Variations of magnetotransport properties of the spin valve, which are due to the formation of antiferromagnetic order in the dysprosium layer, are observed. Peculiarities of noncollinear magnetic order of the Dy layer were found to depend on the direction of magnetic moments of adjacent layers and magnetic field strength when passing through the Néel temperature. [ABSTRACT FROM AUTHOR]

Modern microelectronic devices based on layered spin-valve structures have low power inputs, a high reliability, and a broad temperature range. Studying dynamic spin-valve modes and the possibilities of controlling these modes are of practical interest. In this work, the operating modes of a spin valve, which comprise the base for magnetoresistive random-access memory (MRAM), a binary stochastic neuron (p-bit), and various spin-transfer nanooscillators (STNOs) are considered. A mathematical model of the spin valve with longitudinal anisotropy placed into a magnetic field parallel to the anisotropy axis and perpendicular to the plane of layers is constructed. A set of equations that describe the dynamics of the magnetization vector of the free layer of the spin valve is derived. Quantitative analysis of the set of equations enables determination of the equilibrium positions of magnetization of the free layer for the spin-valve structure. The conditions for changing the type of singular points of the dynamic set of equations are found based on the bifurcation analysis of the set. Investigation into the dynamics of the magnetization vector of the free layer of a spin valve enables determination of its main operational modes as the component of the magnetoresistive random access memory, binary stochastic neuron, and spin-transfer nanooscillator, as well as the ranges of the current and magnetic field corresponding to these modes. The frequency and amplitude characteristics are calculated for spin-valve oscillators. The proposed structure with anisotropy located in a field perpendicular to the anisotropy axis is more preferable when compared to a structure with a field applied parallel to the anisotropy axis from the viewpoint of its application as the spin-transfer nanooscillator. [ABSTRACT FROM AUTHOR]

• The detected amplitude of spin current emitted by spin pumping depends on the NiFe magnetic states. • A spin valve-like behavior with reliable amplitude changes up to 110%. • Paving the road towards ultralow-dissipation spintronic devices based on pure spin current. Ferromagnetic noncollinear spin valve effect has been observed in a magnetic multilayer structure of IrMn/NiFe/Cu/Y 3 Fe 5 O 12 (YIG). In this structure, the detected amplitude of spin current emitted by spin pumping depends on the NiFe magnetic states (saturation or unsaturation). This yields a spin valve-like behavior with reliable amplitude changes up to 110% and the behavior may originate from the difference of spin absorption when the NiFe layer is magnetically saturated or not. Our results provide a ferromagnetic noncollinear spin valve, paving the road towards ultralow-dissipation spintronic devices based on pure spin current. [ABSTRACT FROM AUTHOR]

Spin valves Ta/(Ni80Fe20)60Cr40/Co70Fe20Ni10/Cu/Co70Fe20Ni10/Ru/Co70Fe20Ni10/Fe50Mn50/Ta have been prepared by magnetron sputtering. It was found that the shift of low-field hysteresis loop with respect to H = 0 oscillates as the copper layer thickness changes. Structural studies showed the high perfection of the layer microstructure. Films of spin valves with the copper layer thickness corresponding to the second antiferromagnetic RKKI interaction maximum have been synthesized. They exhibit zero shift of low-field hysteresis loop and are characterized by high magnetoresistance effect. Sensing elements in the form of meanders prepared using the films demonstrate the almost anhysteretical field dependence of magnetoresistance and a magnetoresistive sensitivity of 0.5%/Oe. [ABSTRACT FROM AUTHOR]

Highlights • The sensitivity of stripe-shaped GMR biosensors is limited. • Biological detection in large-area sensors is realized by the reverse nucleation sites under MNPs. • Large-area sensors exhibit better linearity 20 times higher sensitivity. Abstract In the past 20 years, several studies have been performed on the detection of biomarkers by the stripe-shaped spin valve sensors, whose sensitivity is limited by their small sensing area and large sensor resistance. In this paper, large-area spin valve sensors with lower aspect ratio are introduced. A reverse nucleation mechanism is proposed to demonstrate the different switching processes in large-area sensors. The simulation results further prove the involvement of reverse nucleation sites during the magnetization reversal. Large-area sensors also exhibit a linear response to the concentration of magnetic nanoparticles with a sensor signal more than 20 times larger than the stripe sensors. [ABSTRACT FROM AUTHOR]

Highlights • The transmission efficients of Fe 4 N/Ag/Fe 4 N at equilibrium and nonequilibrium are investigated. • The magnetoresistance ratio and spin injection efficient of Fe 4 N/Ag/Fe 4 N at different bias voltages are calculated. • Fe 4 N/Ag/Fe 4 N has a better performance when bias voltage ranges from 0 V to 0.1 V. Abstract Fe 4 N has been confirmed to possess high spin polarization of 81.3% and low Gilbert damping constant of 0.021 ± 0.02 in the recent experiment. To explore the potential applications of Fe 4 N in spintronics devices, the current-perpendicular-to-plane spin valve employing Fe 4 N as electrode and Ag as spacer is simulated to study the spin polarized quantum transport by utilizing the first principles calculations combined with nonequilibrium Green's function. The project density of states (PDOS), transmission coefficient, spin-polarized current, magnetoresistance (MR) ratio and spin injection efficiency (SIE) as a function of bias voltage are studied. Our calculations reveal that spin down electron is the majority spin polarized electron and the absolute value of MR ratio of Fe 4 N/Ag/Fe 4 N at equilibrium reaches up to 174%, and it decreases with the bias increases. Besides, our results indicate that Fe 4 N/Ag/Fe 4 N device has stable SIE value of about 40% and stable MR ratios of about 150% when bias increases from 0 V to 0.1 V, and the device has a better performance within this voltage range. [ABSTRACT FROM AUTHOR]

Highlights • Anhysteretic spin valve meander-shaped sensors are obtained. • Magnetic anisotropy configuration of sensor decreasing the hysteresis is found. • Special thermomagnetic treatment of meander is developed. • Wide U-turns meander allows to create sensor with anhysteretic magnetic reversal. • Sensitivity of sensor is about 0.2%/Oe. Abstract Microsensors (meanders) were fabricated from spin valves with the composition Ta/FeNi/Ru/FeNi/CoFe/Cu/CoFe/Ru/CoFe/FeMn/Ta. Thermomagnetic treatment was used to modify a mutual orientation of magnetic anisotropy and shape anisotropy axes in sensor. Obtained magnetic configuration provides the anhysteretic magnetic reversal of meander. Meanders with different U-turns were investigated and difference in magnetic structure of such meanders was shown. Sensors with high magnetoresistive sensitivity and anhysteretic magnetic reversal were obtained. [ABSTRACT FROM AUTHOR]

This study investigates the observation and control of vortex gyration in the free layer by utilizing polarized current. Modifying the current alone proves challenging in adjusting the frequency and amplitude, as the orbit radius of the vortex core remains constant. To address this, a spin valve nanopillar model with hybrid polarizer is introduced and analyzed, enabling support and gyration of the vortex core in the nanodisk under spin polarized current. Manipulating current density and fine-tuning of hybrid polarizer parameters adjusts system frequency and amplitude. However, with hybrid polarizer, while vortex gyration and higher-frequency signal production increase at higher current densities, the amplitude generally decreases. To mitigate this behavior, the study explores the vortex interactions influenced by magnetostatic coupling in the free layers of spin valve nanopillar. The objective of this paper is to advance the understanding of vortex physics for applications that require greater amplitude microwave signals. [ABSTRACT FROM AUTHOR]

Spintronics is a new field of research exploiting the influence of electron spin on the electrical conduction (or current is spin dependent). The major problem is the realization and fabrication of spintronics based devices. To meet the objective scientific community is developing the novel kind of materials that relies on magnetism instead of flow of current through electron. This paper illustrates and reviews one of the emerging technologies known as spintronics by putting few low power computing techniques altogether based on spintronics to provide a basic and meaningful understanding to the reader. The challenges of spintronics devices that has to meet for the success of electronics future are summarized.

We report a magnetofluidic device with integrated strong ferromagnetically-coupled and hysteresis-free spin valve sensors for dynamic monitoring of ferrofluid droplets in microfluidics. The strong ferromagnetic coupling between the free layer and the pinned layer of spin valve sensors is achieved by reducing the spacer thickness, while the hysteresis of the free layer is eliminated by the interplay between shape anisotropy and the strength of coupling. The increased ferromagnetic coupling field up to the remarkable 70 Oe, which is five-times larger than conventional solutions, brings key advantages for dynamic sensing, e.g., a larger biasing field giving rise to larger detection signals, facilitating the operation of devices without saturation of the sensors. Studies on the fundamental effects of an external magnetic field on the evolution of the shape of droplets, as enabled by the non-visual monitoring capability of the device, provides crucial information for future development of a magnetofluidic device for multiplexed assays.

Abstract: Magnetoresistive random access memory (MRAM) has some advantages over other types of memory. However, MRAM has one substantial drawback: the current density and magnetic field that must be applied to switch the spin-valve free layer inside an MRAM cell are too high. The dependence of the current density and switching magnetic field on the magnetic parameters of the material from which the ferromagnetic layers of a spin valve are fabricated is therefore analyzed. A comparison of the critical characteristics of a spin valve with longitudinal anisotropy shows that cobalt, iron, and alloys of them; cobalt ferroborates; and alloys of cobalt with gadolinium, are promising materials for fabricating spin valves. Bifurcation diagrams of equations that describe the valve switching process are presented and analyzed. The four optimum switching modes of a valve are selected, based on an investigation of the dynamics of the magnetization vector. The magnitudes of the external magnetic field and controlling injection current that correspond to stable MRAM cell switching are compared for a variety of materials. The switching time of an MRAM cell is estimated numerically, and the conditions for its optimum speed are determined. It is established that the most promising materials for spin-valve fabrication are Fe40Co40B20 and Co80Gd20, annealed at 300 and 200°C, respectively. [ABSTRACT FROM AUTHOR]