Search

Modern society is faced with an important challenge – how to ensure enough energy and resources for industrial and population growth and preserve the environment at the same time? The answer lies in the development of novel technologies based on eco-friendly and low-cost materials. In the field of new materials, perovskite oxides stand out due to their multiple properties contained in a single material. The most important are electrical, magnetic and catalytic properties which are the basis for their practical applications. Perovskites were widely investigated over the last 70 years, but perovskite-based technologies have still not reached commercialization. This review presents several novel perovskite-based technologies and addresses possible issues and opportunities for their implementation, based on the recent scientific discoveries.

A molecular spintronics device is considered as a highly promising candidate for the quantum hardware in the field of practical quantum information applications. Within this field, local objects always obey the Coulomb blockade effect, where electrons occupy molecular orbitals monotonically in a step-like manner as the gate voltage sweeps. Herein, based on a single-molecule transistor in an external magnetic field, we predict that the charge occupation of both spin channels may show nonmonotonic filling, characterized by a spin-sensitive charge oscillation, contravening the standard Coulomb blockade behavior. We attribute this nonmonotonicity to the competition among the Zeeman effect, the many-body effect, and the symmetry of the quantum states. To obtain significant oscillations, strong electron–electron interaction and low temperature are prerequisites. We demonstrate that the oscillation goes against the spin-polarized transport, and for appropriate parameters, the transistor may act as a perfect electronically-manipulable bidirectional molecular spintronics device. To implement such an ideal, the state-of-the-art numerical renormalization group method is adopted, and an experimental proposal to test these predictions is suggested.

Ultrafast optical spin control allows gate operations to be performed within a picosecond timescale, orders of magnitude faster than microwave or electrical control. Here, using high-level quantum chemical computations, we suggest a two-qubit logic gate based on the optically induced ultrafast spin-flip and spin-transfer processes over rhombic graphene nanoflakes (Co4-GNF). It is demonstrated that the π-conjugated Co atoms can significantly influence the spin properties of the system. The spin density is distributed on different Co atoms in different energy levels, in this way opening a channel for successful spin-transfer processes between the Co atoms. Thus, the reversible local spin-flip processes on each Co atom and global spin-transfer processes between the Co atoms are realized. Importantly, based on various spin-dynamics processes achieved in Co4-GNF structures, both classical (OR, AND, NAND) and quantum (CNOT, SWAP) two-qubit logic gates are constructed, and the spin manipulation process can be completed in subpicosecond timescale with fidelity above 96%. This theoretical design based on the laser-induced ultrafast spin dynamics provides a new implementation of qubit manipulation, which could pave the way towards the construction of nano magnetic logic circuits and spintronic devices.

Magnetism has revolutionized important technologies, and continues to bring forth new phenomena in emergent materials and reduced dimensions. Here, using first-principles calculations, we demonstrate that the already-synthesized two-dimensional (2D) Ni-tetracyanoquinodimethane (Ni2(TCNQ)2) lattice is a stable ferromagnetism material with multiple spin-polarized Dirac cones. The conical bands in proximity of the Fermi level can be tuned by external tensile strain and show the fourfold degenerate electronic states at the critical tensile strain of ∼2.35%, whose energy dispersion is consistent with 2D Cairo pentagonal lattice. In addition, spin-orbital coupling can open a band gap at the Dirac point of A, leading to topologically nontrivial electronic states characterized by the non-zero Chern number and the edge states of nanoribbon. Our results offer versatile platforms for the realization of massless spintronics with full-spin polarization in 2D Cairo pentagonal Ni2(TCNQ)2 Lattice.

Magnonics is an exciting and rapidly growing field revolving around the study and manipulation of magnons, the low-lying collective excitations of magnetically ordered systems. This field has emerged in response to both fundamental physics interests and the growing demand for faster, more efficient, and more reliable signal processing and computation up to THz frequencies, i.e., beyond clock frequencies of current computer technology. Magnonic devices promise to transmit and process information in ways that are fundamentally different from traditional electronic devices that exploit the flow of charges. Low-frequency spin waves can propagate through magnetic materials with minimal energy loss, transmit information via angular momentum flow instead of charge motion, and can be easily manipulated using magnetic fields, electric fields, spin currents, or thermal gradients. High-frequency magnons offer wave-based in-memory computation at wavelength much shorter than light, contributing to the emerging request for beyond von Neumann computer architectures. Consequently, numerous efforts are focused on developing spin-wave-based approaches to information processing that encode information in the amplitude and phase of spin waves and manipulate it via spin-wave gates and spin-wave interferometers. Magnons also give rise to the new burgeoning field of hybrid magnonics, which aims at leveraging the interactions between magnons and other degrees of freedoms to unlock unprecedented functionalities and physical regimes. In particular, the integration of magnons with other quantum systems, such as superconducting circuits, quantum dots, or nitrogen-vacancy centers in diamond, leads to several advantages for quantum information processing and quantum sensing and opens new avenues for research into the quantum properties of magnons.

Spin Transfer Theory is a promising model for transferring quantum information between spin waves in a spin foam, and using this information to implement quantum computing devices. In this paper, we present a quantum computing perspective on Spin Transfer Theory, and describe how to implement computing devices using quantum circuits. We provide examples of circuits and their corresponding quantum lambdas, which describe the probability distribution of the output states given the input state. Our results demonstrate the potential of Spin Transfer Theory for implementing quantum computing devices.

Spin Transfer Theory is a promising model for transferring quantum information between spin waves in a spin foam, and using this information to implement quantum computing devices. In this paper, we present a quantum computing perspective on Spin Transfer Theory, and describe how to implement computing devices using quantum circuits. We provide examples of circuits and their corresponding quantum lambdas, which describe the probability distribution of the output states given the input state. Our results demonstrate the potential of Spin Transfer Theory for implementing quantum computing devices.

International audience; Magnetism in two-dimensional (2D) van der Waals (vdW) materials has recently emerged as one of the most promising areas in condensed matter research, with many exciting emerging properties and significant potential for applications ranging from topological magnonics to low-power spintronics, quantum computing, and optical communications. In the brief time after their discovery, 2D magnets have blossomed into a rich area for investigation, where fundamental concepts in magnetism are challenged by the behavior of spins that can develop at the single layer limit. However, much effort is still needed in multiple fronts before 2D magnets can be routinely used for practical implementations. In this comprehensive review, prominent authors with expertise in complementary fields of 2D magnetism (i.e., synthesis, device engineering, magneto-optics, imaging, transport, mechanics, spin excitations, and theory and simulations) have joined together to provide a genome of current knowledge and a guideline for future developments in 2D magnetic materials research.

Spintronic-based computing-in-memory (CiM) architecture has emerged as one of the efficient solutions to eliminate the latency/bandwidth bottleneck of conventional von-Neumann architecture. Voltage-controlled spin-orbit torque (SOT) memory offers ultralow power and high-speed operation among the various spintronic memories. In this article, advanced encryption standard (AES) system within CiM architecture using voltage-controlled SOT device has been presented. The entire encryption process is performed within the high-density spintronic-based memory array to achieve low power and high processing speed. The reconfigurable logic operations and random key generation for AES are achieved by using a single voltage-controlled SOT device within the memory array. The results show that the proposed architecture is 96%, 52.1%, and 14% more efficient in terms of energy consumption, throughput, and area, respectively, when compared with one of the most efficient SOT-based AES systems.

Ferromagnetic insulator plays a pivotal role in various emerging spintronic effects and can be integrated as an essential component into future spintronic devices. However, ferromagnetic insulating perovskite oxides are rather scarce due to the strong coupling between ferromagnetism and metallicity via double exchange and superexchange mechanisms, severely restricting the development for oxide-based spintronic devices. Here, the disorder of manganite La2/3Sr1/3MnO3 (LSMO) films grown on MgAl2O4 substrates is utilized to decouple ferromagnetism and metallicity, thereby inducing a ferromagnetic insulating state over a rather broad temperature and thickness range. These films are non-crystalline with enormous disorder. The films with thicknesses less than 16 nm are in completely insulating state, and the films with thicknesses larger than 16 nm are in essentially insulating state with high resistivity. This insulating state is ascribed to the disorder in LSMO films and can be fitted by a localization model. In contrast, all LSMO films exhibit ferromagnetic transitions with considerable saturated magnetic moments and the Curie temperatures near room temperature, leading to the ferromagnetic insulator phase in our manganite heterostructures over a large temperature and thickness interval. Our results broaden the mind for inducing new ferromagnetic insulating state for potential applications in spintronic devices.

Long-range ferromagnetic ordering in semiconductors has become an attractive research hotspot due to its promising potential in spintronics and information technology. Especially the appearance of carbon-based semiconductors represented by graphdiyne (GDY) makes it easy to realize ferromagnetic semiconductors. Herein, a convenient and effective route has been developed to prepare GDY-based magnetic semiconductors using the modification with transition metal elements including Fe, Co, and Ni, respectively. Among them, lightly doped GDY with Co (Co-GDY) exhibits the most outstanding ferromagnetism with a typical Curie's temperature above room temperature. Meanwhile, the coercive field Hc = 78 Oe at T = 300 K of Co-GDY is the smallest, demonstrating characteristics of easy magnetization. Subsequent spin-polarized DFT calculation results reveal that the robust ferromagnetism of Co-GDY arises from the most significant local magnetic moment. Significantly, a noticeable band gap can still be maintained due to the very light doping level. These results reveal an optimization strategy for selecting doping elements, promoting carbon-based semiconductors application in spin-related fields.

RFeO3 is an ideal candidate for the fabrication of spintronic devices, and its rare earth site doping is an important means to regulate and produce many unique spin behaviors. In this work, we report a high-quality Dy0.5Tb0.5FeO3 single crystal grown by optical floating zone method and its magnetic properties are studied explicitly. A type Ⅱ spin switching effect and suppressed spin reorientation transition are found in the Magnetization vs Temperature curves in Dy0.5Tb0.5FeO3. In the temperature region of spin reorientation transition, the transition of Fe3+ magnetic sublattice configuration becomes very complicated by the influence of competitive interaction with magnetic Dy3+/Tb3+ ions. Interestingly, a field tunable double-hysteresis loop is observed near the antiferromagnetic transition temperature of rare earth ions sublattice, which has never been reported in RFeO3 family compounds. By studying the dependence of double-hysteresis loop at different temperatures, the magnetic phase transition and spin reorientation transition induced by the applied magnetic field is inferred. This novel physical phenomenon helps us understand the mechanism of spin configuration transition better at low temperatures.

Magnetic skyrmions have the potential for a wide range of applications in the next generation of spintronics since they are topologically protected spin configurations in the nanometer length scale. In order to be used in the logic gate, it is necessary to consider how to manipulate magnetic skyrmions. At present, the current drive is the mainstream drive, but this method could consume enormous energy for large Joule heating. In this work, the potential well is introduced to drive skyrmion to reduce energy consumption. The potential well is generated by voltage-controlled magnetic anisotropy (VCMA). We study the possibility of the potential well induced skyrmion movement within a certain distance, the relevant factors that affect the distance of skyrmion induction and propose a switched-voltage driving structure within the well-established framework of micromagnetics. Its processes have been theoretically investigated and demonstrated, in which the switched-voltage driving structure can be used to drive skyrmions. Our results provide guidance for the design of low energy consumption voltage-driven skyrmion driving method and a new concept for track memory.

Direct epitaxial integration of magnetic layers with wide bandgap nitride semiconductors will enable spin-controlled transport and photonic phenomena, seeding ideas for functional spintronic devices. Using plasma-assisted molecular beam epitaxy (MBE) in a previously unexplored window, significantly improved ferrimagnetic Mn4N layers are successfully grown on GaN with ~ 1 nm surface roughness. Distinct from earlier reports, the Mn4N layers grown on GaN are found to be 001 oriented with 12-fold in-plane symmetry in the diffraction pattern. This unique epitaxial registry originates from three equivalent rotational domains. The ferrimagnetic magnetotransport properties of low growth temperature Mn4N layers on GaN are comparable to those reported on cubic substrates such as MgO. However, a sign-flip of the Hall resistance is discovered for Mn4N layers grown above 300 °C.

We report the magnetovolume effect of quaternary Heusler alloy CoFeCrAl as a potential candidate of spin gapless semiconductor. The crystal structure of CoFeCrAl was confirmed as the single phase of the ordered LiMgPdSn-type structure. From magnetization measurements at ambient pressure, the Curie temperature TC and the spontaneous magnetization Ms were determined to be 575.2 K and 2.01 μ B/f.u., respectively. The TC is higher enough than room temperature and the Ms follows the Slater-Pauling rule. High-pressure magnetization measurements showed that the Ms is almost independent of applying pressures not only at 10 K but also up to 300 K, exhibiting that the electronic state of CoFeCrAl is fully spin polarized and it is preserved even at 300 K. The experimental results reveal that the quaternary Heusler alloy CoFeCrAl is an attractive material for functional electrode ferromagnets in spintronics devices.

The effect of the interfacial Dzyaloshinskii-Moriya interaction (i-DMI) on the magnetization dynamics induced by strain is described within the framework of micromagnetic simulations taking into the magnetoelastic coupling between the spin and strain in multiferroic heterostructures. In this magnetized system, biaxial in-plane strain act on the perpendicular magnetization without bias magnetic field is introduced. As the micromagnetic simulation results have shown, the lateral magnetization dynamics and spin wave were excited with the i-DMI induced intrinsic magnetization tilting along the nanostrip width direction. It is found that the excitation strain field could generate a quantized width mode with odd mode numbers. In addition, our simulation reveals that the excitation field with higher frequency generates two spin wave modes with a different mean free path. Our works, therefore, show the potential of using a strain with the presence of i-DMI as the perspective for integrating spin wave emitters into future logic or computing devices and hinting at possible technological applications in strain-controlled spintronic systems.

Exchange bias is a complex interface phenomenon often used in multiple applications ranging from magnetic field sensors to spintronics and neuromorphic computing for inducing a unidirectional anisotropy in a ferromagnetic layer exchange coupled to an antiferromagnetic layer. Despite the significant progress in understanding mechanisms behind the exchange bias, predicting and optimizing hysteresis properties of the pinned layer in real-life systems with complex crystalline and magnetic structure is still a challenge. In this work we use a combined machine learning and micromagnetic simulation approach for building a unified predictive model giving macroscopic hysteresis properties of the pinned layer for a given set of magnetic and structural parameters. The approximator can be considered as an unknown function, which can be used for finding local or global extrema for coercivity or exchange bias field. We believe that a similar approach can be applied to other computer models or high-quality experimental data for advanced analysis of functional dependencies of hysteresis properties as well as evaluation of computer model used for simulation. A machine learning model of a bilayer with exchange bias could be helpful for decreasing the computation time, optimizing layers materials and parameters, and minimizing the number of test samples.

Skyrmions are found to be promising for next generation energy efficient spintronic applications. Moreover, ultrafast skyrmion dynamics in GHz-band offer an excellent opportunity to exploit such topologically protected nanostructures in high frequency applications. Here, we present a systematic investigation on the microwave properties of the skyrmions in concentric and eccentric ring structures using micromagnetic simulations. Two gyrotropic modes with clockwise and counter-clockwise gyration are observed in skyrmion when excited by an in-plane microwave field. The high frequency response is found to be enhanced by 3.5 GHz by using a small bias field of 40 mT. The skyrmion dynamics are found to be extremely sensitive to the edge repulsions and a remarkably large frequency shift of 2 GHz of the skyrmion resonance modes is observed by simply varying the position of a skyrmion in an eccentric ring structure. The results are substantiated by directly correlating the observations with inertial mass associated with a skyrmion calculated analytically. The results provide an additional functionality of the skyrmions based on their tunable microwave properties which may have potential implications in the field of miniaturized reconfigurable microwave devices.

Over the past four years, the magnetism of 2D magnets has been extensively studied by the full arsenal of probing techniques. 2D magnets can be incorporated to form heterostructures with clean and sharp interfaces, which gives rise to exotic phenomena as a result of the interfacial proximity effect. Here we report a detailed study of the spin (ms) and orbital (ml) moments of an epitaxial (CrSb/Fe3GeTe2)6 superlattice. The synchrotron-radiation based x-ray magnetic circular dichroism (XMCD) technique was performed to probe the microscopic magnetic properties of the superlattices in an elemental resolved manner. We unambiguously obtained a bulk-like moment of Fe3GeTe2 i.e., ms = 1.58 ± 0.2 μB/Fe and ml = 0.22 ± 0.02 μB/Fe. Future works to explore the tuning of the spin polarized band structure of 2D ferromagnetic superlattices will be of great interest and can have strong implications for both fundamental physics and the emerging spintronics technology.

We report the critical behavior of the magnetization in Heusler alloy Co2TiGa0.8Sn0.2 as a potential candidate of high spin polarized materials with the characteristics of topological Weyl fermions. The Weyl semimetals are materials of great interest for applying spintronics devices, due to their unusual magnetoelectronic and magnetothermal properties. The magnetic properties of the synthesized Heusler alloy Co2TiGa0.8Sn0.2 are investigated around the Curie temperature TC. The magnetic isotherm measurements of Co2TiGa0.8Sn0.2 around TC exhibit that the critical exponent δ is deduced to be 4.455(4) in high maximum applied field of 50 kOe and 4.823(9) in low maximum applied field of 10 kOe, respectively. Both δ values are different from 3.0 derived by the conventional molecular field theory, but they are close to 5.0 predicted by the spin fluctuation theory for the itinerant electron ferromagnets. Possible origins for the discrepancy between experimental results and theoretical models are also discussed.

Post-neodymium magnets that possess high heat resistance, coercivity, and (BH)max are desired for future-generation motors. However, the candidate materials for post-neodymium magnets such as Sm2Fe17N3 and metastable magnetic alloys have certain process-related problems: low sinterability due to thermal decomposition at elevated temperatures, deterioration of coercivity during sintering, and the poor coercivity of the raw powder. Various developments in powder processing are underway with the aim of overcoming these problems. So far, the development of advanced powder metallurgy techniques has achieved Sm2Fe17N3 anisotropic sintered magnets without coercivity deterioration, and advances in chemical powder synthesis techniques have been successful in producing Sm2Fe17N3 fine powders with huge coercivity. The challenge of a new powder process is expected to open the way to realizing post-neodymium magnets., GRAPHICAL ABSTRACT

Although coercivity is one of the fundamental properties of permanent magnets, it has not been well understood. In this paper, micromagnetics and thermal activation magnetization reversal theories are briefly reviewed, and then our recent macroscopic and microscopic experimental approaches for thermally activated magnetization reversal in advanced Nd-Fe-B hot-deformed magnets are explained. Our experimental results are well supported by the recent atomistic spin model calculations. Moreover, the systematic micromagnetics simulation study makes much clearer the physical picture of the thermally activated magnetization reversal process in permanent magnets., Graphical abstract

Among the semiconductor metal oxides, some semiconductor structures are identified for their unique and vast potential applications in optoelectronic, field effect transistors, solar cells, photoluminescence devices, and diluted magnetic semiconductors, etc. The interesting development in optoelectronic applications arises due to environmentally friendly short energy, laser diodes and white light producing technologies that work beyond room temperature. Out of this ZnO is an adaptable material for scientific study. The variation of ZnO properties by insertion of impurity/dopant has turn into a recent emerging matter. The phenomena of doping in ZnO i.e. ZnO as a host material will create by researchers; tailoring its optical, structural, electrical and magnetic properties through modifying its electronic structure. Due to doping results, there is enhancement in diverse applications like electronic, spintronic, optoelectronic, photocatalytic, antibacterial, etc. These improvements in different application areas are due to its direct band gap energy, luminescence, high electron mobility, and debatable room-temperature ferromagnetic conduct in diverse structures like single crystals, thin films, powders and nanostructure. This review extensively focused on the comprehensive cross-section of ZnO’s luminescent, structural, optical, magnetic properties and various applications, with the key directions of development, serving as beginning, an orientation, and stimulation for upcoming research.

Full potential LAPW + lo method is used for exploring electronic, structural and thermoelectric properties for MgNd2X4 (X = S, Se) spinels that are found to show ferromagnetic-semiconductor behaviour in the spinel structure. The investigated negative value of formation energy and positive value of phonon spectra computed using PBEsol GGA indicates the energetic and dynamical stability of the studied cubic ferromagnetic-semiconductors. We have used TB-mBJ potential functional for electronic and magnetic properties, which lead to a reliable account of electronic structure, demonstrating band occupancy in the spinels along with a clear explanation of density of states. The stability of ferromagnetic state in the studied materials is because of the exchange splitting of Nd cations based on p-d hybridization which is in accordance with the results obtained for electronic band structure and density of states. The exchange splitting of bands can be justified by the spin magnetic moment between anions and cations, and sharing of charge. The computed values of dielectric constant and their associated optical parameters are used to explain the optical active behaviour of the spinels under investigation; indicating that the two spinels studied in the present work are suitable for solar cells device applications. The calculation of thermoelectric properties is very useful for determining a material's potential use in waste energy recovery systems and many other innovative applications.

Excellent magnetoresistive materials have attracted people's attention due to their wide applications. Unfortunately, few cobalt-based perovskite oxides can demonstrate good magnetoresistance (MR) properties. Herein, a new series of SrCo1-xFexO2.9-δF0.1 (x = 0, 0.1, 0.2, and 0.3) perovskites are prepared and studied as potential magnetoresistive materials. Room temperature X-ray diffraction (XRD) and Rietveld refinement confirm the simple cubic structure of all samples. The magnetization vs temperature measurement reveals that the magnetic transition temperature goes down with the increase of Fe content, suggesting the weakened ferromagnetism caused by Fe4+-O-Co3+, Fe3+-O-Fe3+ and Fe4+-O-Fe4+ interactions. And the resistivity data of all Fe doped samples can be better fitted using Mott's variable range hopping (VRH) model, suggesting its disordering semi-conduction behavior. Astonishingly, the SrCo0.8Fe0.2O2.9-δF0.1 ceramic sample owns the giant negative magnetoresistance value of approximately 90% at 5 K in 90 kOe, which is almost the largest negative magnetoresistance in cobalt-based perovskite oxides, indicating that cobalt-based perovskites can be an underlying material system for the research of the potential material applying to magnetic sensors or other spintronic devices.

In last decades, open-shell organic materials have attracted scientists’ great attention for their new chemical and physical properties, as well as their possible applications in new generation of organic light-emitting diodes (OLEDs), organic field effect transistors (OFETs), organic spintronics and photonics, and so on. In this review, we summarize the recent progress of design and synthesis of open-shell organic magnetic materials. Especially, we will focus on their aggregated states in OFETs, organic conductors and luminescent devices and photoinduced radical materials, with the aim to provide some clue for the further development of novel open-shell organic magnetic materials.

A large variety of recently predicted and synthesized 2D materials significantly broaden capabilities of magnetic interfaces design for spintronics applications. Their diverse structural and electronic properties allow finely adjust interfacial interaction between electrode and spacer materials providing robust and effective spin transport. Based on recent experimental results, here we present a theoretical study of novel interfaces formed by half-metallic Co2FeGe1/2Ga1/2 (CFGG) substrate with h-BN or MoSe2 monolayer on its top. By means of DFT approach structural, magnetic and electronic properties are studied for Co- and FeGeGa termination of CFGG surface. Found large spin polarization in the vicinity of the interface and robust magnetization support a promise of 2D materials/Heusler alloy heterostructures for spintronics needs.

A method of preparing passive materials suitable for magnetooptic interactions is shown using manganese implantation into gallium nitride (GaN) epitaxial layers, which establishes both dilute ferromagnetism and a three-level optical system with persistence to over 300 K. A sweep of thermal anneal parameters for a high implant dose into Mg-doped p-type GaN films is presented, and the materials are tested for both their magnetization and photoluminescence (PL). The optimal anneal process at 825 °C for 5 min maintains ferromagnetism with $T_{C}$ > 305 K, confirming magnetic alignment at room temperature with a coercivity of ~100 Oe. PL and spectrophotometry of the optimally prepared materials show the effects of the mid-gap defect state on the material's optical characteristics. The anneal process returns the real part index to its baseline dispersion while retaining an onset of absorption starting at the defect level $E_{A}$ = 1.8 eV, signifying a stable mid-gap energy transition with a measured state lifetime of $τ _{PL}$ = 2.7 ns. The scalability of this process for producing three-level transition magnetic materials suggests passive optical or magnetooptic devices can be constructed that interconnect photonic and spintronic effects for emerging system designs and potential applications in quantum information.

Exploiting two-dimensional room temperature ferromagnetic materials is always a significant and valuable work. However, the actual number of satisfied materials with intrinsic ferromagnetism is very limited. Here, the van der Waals Cr4Te5 epitaxial films prepared by pulsed laser deposition technique were confirmed to hold ferromagnetic ordering state until to 300 K. We find that the Cr4Te5 films can easily achieve the epitaxial growth along a single orientation for the hexagonal Al2O3(0001) substrate. However, as for cubic SrTiO3(001) and multiphase structure Mica substrate, the Cr4Te5 films only show an uniaxial growth instead of epitaxial growth. Based on the investigation of electronic transport in metallic regime, it is revealed that the interaction of electronmagnon scattering only exists in the lower temperature region. Our work render two-dimensional vdW Cr4Te5 crystal a very promising material for developing practical spintronic nanodevices.

Half-Heusler alloys are prominent material for spintronics devices as these materials usually exhibit high spin polarization. But this spin polarization is severely affected by various disorders and distortions which ultimately hinders their practical applications. This paper examines the effect of the uniaxial strain as well as the tetragonal strain on the electronic and magnetic properties of half-Heusler FeCrAs alloy. This work is carried out by using the first-principles density functional theory calculations using the Wein2k software. The results of our study show that FeCrAs alloy exhibiting AFM and FM characteristics in u- strain while showing only FM characteristics in t- strain. The Half metallicity of the FeCrAs is sensitive in negative u-strain while it is quite robust in positive u-strain and t-strain the FeCrAs. The maximum value of band gap at 0% tetragonal-strain is about 1.04 eV. The FeCrAs Heusler alloy preserve the 100% spin polarization for whole studied range of tetragonal-strain (−10% to 10%). This property may make this system a promising candidate for spin transfer torque application.

The advancement in synthesis techniques provide the opportunity to synthesis the sample with uniform size, desired morphology and enhanced property for specific application. The role of semiconductor in various optoelectronic, spintronics and memory device has been approved by available literature. The emergence of semiconductor quantum dot opens new possibility to improve the performance of semiconductor-based device as well as new application due to quantum confinement phenomenon. The confinement of charge carries leads toward the tuning of electrical conductivity, band gap and magnetic nature of semiconductor. This work is focused on study of CdSe and CdTe semiconductor quantum dot and corresponding change in their properties by quantum confinement. The applications along with different dopant ion have been summarised through table and supported by literature.

Organic semiconductor single crystals (OSSCs) possess high mobility and ultra-long spin relaxation times in the millisecond or even second range, mainly due to their pure material systems, perfect periodic structures, and inherent weak spin–orbit coupling (SOC). Coupling this with their excellent photoelectric functionality, they have long been considered as perfect materials for organic spintronic applications to obtain both long-distance spin transport and novel multifunctionality at room temperature, attracting wide interest. Currently, spintronic studies based on OSSCs are still at the heuristic stage, and there are many related critical challenges, as well as important opportunities. Herein, this perspective article, relying on developed theory and in-depth investigations of organic semiconductors (OSCs) in electronics and spintronics, provides discussion and future prospects, focusing on several aspects of OSSCs; we aim to inspire progress in this new field and attempt to guide a wide range of research in related fields. Firstly, as the spin relaxation time and charge carrier mobility are the two main factors affecting the spin diffusion length, the effects of the molecular structure and stacking structure regarding these two factors are discussed, covering material design and regulation methods in detail. Then, the current situation and challenges relating to device fabrication technology based on OSSCs are outlined, highlighting what needs to be solved in order to build a foundation for achieving extra-long spin transport in OSSCs and novel multifunctional OSSC-based spintronic devices. Finally, based on various reported multifunctional spintronic devices and OSSCs with excellent photoelectric properties, the exploitation of novel multifunctional spintronic devices is discussed.

[EN] The structurally simple complex {Fe-II[tren(6F-py)(3)]}(BF4)(2) [tren(6F-py)(3) = tris(3-aza-4-(6-fluoro-2-pyridyl)-3-butenyl)amine] undergoes an abrupt spin transition (ST) with the critical temperature T down arrow(1/2) = 243 K on cooling and T up arrow(1/2) = 281 K on heating, with a 38 K wide hysteresis, while the ClO4- congener shows ST spanning the room temperature region at T down arrow(1/2) = 267 K and T up arrow(1/2) = 295 K with a 28 K wide hysteresis. Calorimetric data confirm the occurrence of a highly energetic ST process, while multi-temperature single crystal X-ray structural studies identify a concerted symmetry-breaking P2(1)/n P2(1)/c as the origin of the rare strong cooperativity and the large hysteresis loop. The analysis of the experimental data discloses two distinct interdependent events, namely, the combination of a gradual ST and an induced crystallographic phase transition, which endows the material with strong bistability and makes it an excellent platform for investigating new generations of ST based electronic and spintronic devices., This work was supported by grant PID2019-106147GB-I00 funded by MCIN/AEI/10.13039/501100011033, Unidad de Excelencia Maria de Maeztu (CEX2019-000919-M); the Generalitat Valenciana through PROMETEO/2016/147 and EU Framework FET-OPEN project COSMICS (grant agreement 766726), by the grant of the Ministry of Education and Science of Ukraine for perspective development of a scientific direction "Mathematical sciences and natural sciences" at Taras Shevchenko National University of Kyiv. We thank Prof. Dr Eric Collet for invaluable comments and suggestions.

Manipulating physical properties using the spin degree of freedom constitutes a major part of modern condensed matter physics and is a key aspect for spintronics devices. Using density functional theory calculations, we predict that the spin direction can be controlled in nonmagnetic BX/MX2 (M = Mo or W; X = S, Se and Te) van der Waals heterostructures. The stability of the heterostructures is proved by calculating their binding energies and phonon dispersion plots. The electronic structures of the heterostructures demonstrate that all of them maintain the semiconducting nature, but have different band alignment, which is related to orbital components at the band-edge and influenced by the electron transfer at the interface. With considering the spin-orbit coupling, the Rashba-type spin splitting with in-plane spin and valley polarization with out-of-plane spin can be formed and coexistence at the valence-band of BSe/MoSe2 and BSe/WSe2. Moreover, the dominated carrier spin direction around the valence-band edge can be effectively tuned by exerting biaxial strain and external electrical field. These calculations show that manipulate spin within semiconductor devices to exploit the full potential of materials with a gap for charge control without the use of auxiliary ferromagnetic materials and magnetic fields can be achieved in the newly discovered two-dimensional van der Waals system.

We report on results pertinent to the room temperature First Order Reversal Curve (FORC) analysis of Inverse Heusler alloy Fe2CoSi thin films with different thicknesses (t = 5, 10, 15 and 20 nm). Our analysis infers that magnetostatic interactions between magnetic grains enhance with an increase in the thickness of Fe2CoSi thin films. Indeed, such results are confirmed with the analysis of switching field distribution (SFD). Single domain (SD) to multi domain (MD) transformation is evidenced as the thickness increases from 5 to 20 nm. Single domain state is confirmed by symmetric contour around Bu = 0 axis, while, multidomain state is affirmed with no central peak and spreading of contour parallel to Bu = 0 axis. The change in domain state configuration for different thicknesses might strengthen the application of Fe2CoSi Heusler alloy films for the future spintronic applications.

The scarcity of two-dimensional (2D) magnetic nanostructures has hindered their applications in spintronics, which is attributed to that most magnetic materials exhibit non-van der Waals (nvdWs) structure and it is hard to reduce their thickness to 2D nanostructures. Thus it is eager to develop a promising strategy for free-standing 2D magnetic nvdWs nanostructures. We have achieved free-standing 2D nvdWs hexagonal FeSe with a thickness of 2.9 nm by the reaction between oleylamine-Se complex and Fe2+ with the assistance of Cl-, where the synergetic effects of Cl- and -NH2 lead to the anisotropic growth. Inspiringly, the 2D hexagonal FeSe exhibits intrinsic antiferromagnetic order rooted in Fe2+ and semiconductor nature. In addition, the temperature variation would result in the chemical environment changes of Fe2+, responsible for the temperature-dependent magnetic transitions. This work promotes the potential applications of 2D hexagonal FeSe and the preparation of other 2D nvdWs materials.

A Universal Mathematical Field Theory (UMFT) is established, which states that the combination of the operations of both gradient and divergence of vector fields, such as electric field and velocity field, create the curl of an axial vector field, such as magnetic field. Utilizing UMFT, we mathematically: (1) derive the Extended-Maxwell equations and the Lorentz force from Coulomb’s law and the velocity of the source; (2) establish Maxwell-type gravitational equations and Lorentz-type gravitational force (Gravito-EM) from Newton’s law and velocity of gravitational source; (3) establish Classical-Spin-Electromagnetism (Spin-EM) from the Coulomb’s law and the spin of the spin angular velocity; (4) predicate the Spin related force. For a source moving with non-spatially-varying velocity the Extended-Maxwell equations reduce to Maxwell equations, which justifies UMFT and shows that the experiments-based Maxwell equations have mathematical origin. This derivation mathematically explains how a moving electric charge creates magnetic field, and shows that there is no magnetic monopole charge. UMFT shows that mathematical identities lead to physical dualities including duality between EM and Gravito-EM. The concepts, effects and phenomena of EM may be directly converted to that of gravity. The Gravito-EM are employed to study the accelerating universe, rotation curve and gravitation waves. The Gravito-EM can be quantized, along the line of quantizing EM, and unified with EM force. We derive, for the first time, the Spin-Lorentz-type force and Lagrangian-Lorentz-type force. If experimentally proved, the Spin-related force may be the 5th force. UMFT provides mathematical origins of physical dualities between Extended EM, Gravito-EM and Spin-EM.

We have designed a passive spintronic diode based on a single skyrmion stabilized in a magnetic tunnel junction and studied its dynamics induced by voltage-controlled anisotropy (VCMA) and Dzyaloshinskii-Moriya interaction (VDMI). We have demonstrated that the sensitivity (rectified voltage over input microwave power) with realistic physical parameters and geometry can be larger than 10 kV/W which is one order of magnitude better than diodes employing a uniform ferromagnetic state. Our numerical and analytical results on the VCMA and VDMI-driven resonant excitation of skyrmions beyond the linear regime reveal a frequency dependence on the amplitude and no efficient parametric resonance. Skyrmions with a smaller radius produced higher sensitivities, demonstrating the efficient scalability of skyrmion-based spintronic diodes. These results pave the way for designing passive ultra-sensitive and energy efficient skyrmion-based microwave detectors., Comment: 11 pages, 3 figures

Antiferromagnetic materials have been proposed as new types of narrowband THz spintronic devices owing to their ultrafast spin dynamics. Manipulating coherently their spin dynamics, however, remains a key challenge that is envisioned to be accomplished by spin-orbit torques or direct optical excitations. Here, we demonstrate the combined generation of broadband THz (incoherent) magnons and narrowband (coherent) magnons at 1 THz in low damping thin films of NiO/Pt. We evidence, experimentally and through modeling, two excitation processes of spin dynamics in NiO: an off-resonant instantaneous optical spin torque in (111) oriented films and a strain-wave-induced THz torque induced by ultrafast Pt excitation in (001) oriented films. Both phenomena lead to the emission of a THz signal through the inverse spin Hall effect in the adjacent heavy metal layer. We unravel the characteristic timescales of the two excitation processes found to be 300 fs, respectively, and thus open new routes towards the development of fast opto-spintronic devices based on antiferromagnetic materials.

To extend current charge-based electronics by new features and functionalities, the electron spin, as a new degree of freedom, is likely to play a major role in future information technology. Devices using such spin-based electronics (spintronics), for example magnetic random-access memories, are about to enter the market. To be competitive with other information carriers, it is required to push the bandwidth of the elementary spintronic operations to the terahertz (THz) frequency range. This thesis addresses central open questions regarding ultrafast spin transport in prototypical FjN thin-film stacks. Is ultrafast spin transport mediated by magnons as universal as indicated by previous modelling? What impact does the F/N interface between F and N have on the ultrafast spin-to-charge current conversion (S2C)? How can we exploit spintronic features for new functionalities of spintronic THz emitters (STEs)? By studying spin current dynamics on their natural timescale, one may find new interesting effects or push existing concepts to THz frequencies, which might advance future spintronic applications to work at higher clock rates. To study ultrafast spin transport in FjN bilayers, we excite them with femtosecond laser pulses. Following absorption of the pulse, a spin current in F is launched and converted into a transverse charge current in N and/or F, giving rise to the emission of a THz electromagnetic pulse. Using this approach, along with an analysis based on symmetry arguments and modeling, the following insights are gained: First, depending on the conductivity of F, spin currents can be carried by either (i) conduction electrons or (ii) magnons. Remarkably, in the half-metallic ferrimagnet Fe3O4 we observe the coexistence of these two spin transport types and disentangle them based on their distinctly different ultrafast dynamics. Our results also indicate that the ultrafast SSE spin current is localized close to the F/Pt interface and its ultrafast dynamics are determined by the relaxation dynamics of the electrons in the Pt layer. Second, interfaces of metallic heterostructures are known to have a marked impact on the S2C process. We study thin metal lms of a ferromagnetic layer F and nonmagnetic layer N with strong and weak spin-orbit coupling. Varying the interface composition allows us to drastically change the amplitude and even invert the polarity of the THz charge current. Symmetry arguments and first-principles calculations strongly suggest that the interfacial S2C arises from skew scattering of spin-polarized electrons at interface imperfections. Third, we add a functionality to the STE and modulate the polarization of broadband THz electric field pulses at tens of kHz by time-dependent external magnetic field with a contrast exceeding 99 %. In conclusion, THz emission spectroscopy is a powerful tool to explore and exploit spintronic effects in the ultrafast regime, which will lay the cornerstone for spintronics at THz frequencies., Bei der Weiterentwicklung heutiger Elektronik um neue Funktionen und Funktionalitäten wird der Elektronenspin als zusätzlicher Freiheitsgrad in künftiger Informationstechnologie voraussichtlich eine tragende Rolle spielen. Geräte, die solche spinbasierte Elektronik nutzen (Spintronik), wie zum Beispiel magnetische Random-Access Speicher, stehen kurz vor der Markteinführung. Um mit anderen Informationsträgern konkurrenzfähig zu sein, muss die Bandbreite der grundlegenden spintronischen Operationen auf den Terahertz-Frequenzbereich (THz) ausgeweitet werden. Diese Arbeit befasst sich mit zentralen offenen Fragen zum ultraschnellen Spintransport in prototypischen FjN-Dünnschichtstapeln. Ist der ultraschnelle, durch Magnonen vermittelte Spintransport so universell, wie es das bisherige Modell nahelegt? Welchen Einfluss hat die F/N-Grenzfläche auf die ultraschnelle Spin-Ladungsstrom-Umwandlung (S2C)? Wie können spintronische THz-Emitter (STEs) um neue Funktionalitäten erweitert werden? Durch die Untersuchung der Spinstromdynamik auf ihrer natürlichen Zeitskala könnten neue Effekte entdeckt oder bestehende Konzepte spintronischer Anwendungen auf THz-Frequenzen ausgedehnt werden. Um den ultraschnellen Spintransport in FjN-Bilagen zu untersuchen, regen wir diese mit Femtosekunden-Laserpulsen an. Nach Absorption des Pulses wird ein Spinstrom in F erzeugt und in einen transversalen Ladungsstrom in N und/oder F umgewandelt, was zur Emission eines elektromagnetischen THz-Pulses führt. Mit diesem Ansatz und einer Analyse auf der Grundlage von Symmetrieargumenten und Modellen werden die folgenden Erkenntnisse gewonnen: Erstens können Spinströme, je nach der Leitfähigkeit der F-Schicht, entweder von (i) Leitungselektronen oder (ii) Magnonen getragen werden. Bemerkenswerterweise beobachten wir im halbmetallischen Ferrimagneten Fe3O4 die Koexistenz dieser beiden Spintransporttypen und können sie aufgrund ihrer deutlich unterschiedlichen ultraschnellen Dynamik voneinander trennen. Unsere Ergebnisse zeigen auch, dass der ultraschnelle Spin Seebeck-Spinstrom in der Nähe der F/Pt-Grenzfläche lokalisiert ist und seine ultraschnelle Dynamik durch die Relaxationsdynamik der Elektronen in der Pt-Schicht bestimmt wird. Zweitens die Grenzfläche metallischer Heterostrukturen ist bekannt für ihren Einfluss auf den S2C-Prozess. Wir untersuchen dünne Metallfilme mit einer ferromagnetischen Schicht F und einer nichtmagnetischen Schicht N mit jeweils starker und schwacher Spin-Bahn-Kopplung. Durch Variation der Grenzfläche können wir sowohl die Amplitude drastisch verändern, als auch die Polarität des THz-Ladungsstroms umkehren. Symmetrieargumente und First-Principle Berechnungen legen nahe, dass die S2C an der Grenzfläche durch Skew-Streuung von spinpolarisierten Elektronen an Grenzflächenfehlstellen entsteht. Drittens erweitern wir den STE um eine Funktionalität und modulieren die Polarisation breitbandiger THz-Pulse bei Dutzenden von kHz durch zeitabhängige externe Magnetfelder mit einem Modulationskontrast größer 99%. Zusammenfassend erweist sich THz-Emissionsspektroskopie als leistungsfähiges Instrument zur Erforschung und Anwendung von spintronischen Effekten, die den Eckpfeiler für die THz-Spintronik bilden werden.

Spintronic devices, supplementing and surpassing charge-based electronics by including the electron spin, have recently begun to reach the market. Information carriers such as electrons (in field-effect transistors) and photons (in optical fibers) have already reached the terahertz range (THz, 10^12 Hz). To make the electron spin compatible and competitive, spintronic operations need to be pushed to THz frequencies. So far, is is unclear whether fundamental spintronic effects such as spin accumulation or spin-orbit torque can be transferred to THz frequencies. In this respect, it is also important to note that the THz range coincides with many fundamental excitations, for instance phonons, magnons, and the relaxation of electronic currents. Strong THz electromagnetic pulses can be used to study such fundamental excitations, making use of both the electric and magnetic fields of the electromagnetic pulse. In this thesis, strong THz electromagnetic pulses are applied to spintronic thinfilm stacks to drive charge and spin currents, apply torque and manipulate magnetic order. A short optical probe pulse or a resistance probe interrogate the transient magnetic response. First, a measurement strategy is developed to simultaneously detect all components of the vector magnetization of thin film magnets in optical transmission probe experiments at normal incidence, requiring only a variation in the initial probe polarization. To this end, the magnetic circular and linear birefringence (MCB, MLB) effects are measured simultaneously and a calibration strategy for the often neglected MLB effect is presented. Second, using this detection scheme, we study the THz frequency operation of spintronic effects in ferromagnetic(FM)/non-magnetic (NM) heavy metal stacks. We find signatures of THz spin accumulation at the FM/NM interface. The spins injected into a ferromagnet relax within ∼ 100 fs, in line with electron-spin equilibration times measured by ultrafast optically induced demagnetization. Indications of the field-like spin-orbit torque (FL-SOT) are found. Third, an effective method to modulate the relative THz electric and magnetic field amplitudes in thin film samples is presented, enabling one to disentangle effects driven by the electric or the magnetic component of the THz electromagnetic pulse. A nearperfect conductor (THz mirror) quenches the THz electric field in a region close to the mirror, while doubling the THz magnetic field. Measurements with a ferromagnetic thin film confirmed a THz magnetic field increase of 1.97 ± 0.06 and a suppression of the THz electric field in the sample. Finally, we utilize the electric-field suppression effect close to metals to optically gate the THz electric field driven resistance modulation of an antiferromagnet (AFM) grown on a semiconducting substrate. An optically induced transient substrate conductance depletes the THz electric field in the AFM layer, while not perturbing the AFM magnetic order directly. A simple model of parallel conductances is presented, confirming the experimental observations. In conclusion, this thesis is an important contribution to push fundamental spintronic effects such as spin accumulation and spin-orbit torque to the THz range. The developed methodologies are helpful to advance nonlinear THz spectroscopy of magnetic materials., Da die ersten auf spintronischen Prinzipien erbauten Speicher den Markt erreichen und gleichzeitig Informationsträger wie Elektronen (in Feldeffekttransistoren) und Photonen (in Glasfaserkabeln) in den Terahertz-Frequenzbereich (THz, 10^12 Hz) vordringen, stellt sich die Frage, ob die Spintronik, welche die Elektronik um den Elektronenspin erweitert, mit solch hohen Frequenzen kompatibel ist. Gleichzeitig ist der THz-Frequenzbereich, welcher elementare Anregungen wie Phononen und Magnonen enthält, auch fur die Grundlagenforschung interessant. Um diese Anregungen zu untersuchen bieten sich elektromagnetische THz-Pulse mit hohen Feldstärken an, denn sie können direkt an elektrische und magnetische Resonanzen koppeln. Diese Arbeit untersucht mit THz-Lichtpulsen, die in spintronischen Dünnfilmproben Spin- und Ladungsströme induzieren, ob elementare spintronische Effekte, wie die Spin-Akkumulation oder das Spin-Bahn-Drehmoment, auch bei THz-Frequenzen aktiv sind. Die magnetische Antwort wird mit kurzen optischen Pulsen oder mittels elektrischer Messungen zeitaufgelöst abgefragt. Die spintronischen Effekte werden in ferromagnetischen (FM)/nichtmagnetischen (NM) Dunnfilm-Metallmultilagen untersucht, wobei zuerst eine Messmethode erarbeitet ¨ wird, um alle räumlichen Anteile der Probenmagnetisierung gleichzeitig zu bestimmen. Hierzu werden die magnetische zirkuläre Doppelbrechung (MCB) und die, oft vernachlässigte, magnetische lineare Doppelbrechung (MLB), welche der Abfragepuls beim Durchdringen der Probe entlang der Probennormale erfährt, gleichzeitig bestimmt. Ein besonderes Augenmerk liegt auf der Normierung des MLB-Signals. Mithilfe dieser neuartigen Messmethode werden Indizien fur eine THz Spin-Akkumulation und das feldartige Spin- ¨ Bahn-Drehmoment (FL-SOT) an der FM/NM Grenzfläche gefunden, welche auf einen Spinaustausch zwischen dem nichtmagnetischen Schwermetall und dem FM zuruckgeführt ¨ werden. Die in den FM eindringenden Spins relaxieren auf einer Zeitskala von ∼ 100 fs, was mit Ergebnissen aus ultraschnellen optischen Demagnetisierungsstudien ubereinstimmt. ¨ Zusätzlich wird die nichtlineare THz-Spektroskopie dahingehend erweitert, vom elektrischen oder magnetischen THz-Feld getriebene Signale unterscheiden zu können, indem die relativen Stärken der elektromagnetischen Felder im Inneren einer Dunnfilmprobe beeinflusst werden. Hierbei unterdruckt ein elektrisch leitender THz Spiegel das THz elektrische Feld in der Probe, während das THz magnetische Feld um einen Faktor 1.97±0.06 verstärkt wird. Diese Unterdruckung des THz elektrischen Feldes in der Nähe eines Leiters wird genutzt, um die vom THz elektrischen Feld getriebene Widerstandsmodulation in einem, auf einem (optisch angeregten) halbleitenden Substrat gewachsenen, Antiferromagneten (AFM) zu steuern. Dabei wird die Wirkung des THz elektrischen Feldes im AFM unterdruckt ohne den magnetischen Zustand des AFM zu stören. Ein einfaches Modell stutzt die Interpretation der Beobachtungen. Zusammenfassend leistet diese Arbeit einen wichtigen Beitrag, um spintronische Effekte wie die Spin-Akkumulation und das Spin-Bahn-Drehmoment im THz-Frequenzbereich zu etablieren und erweitert zusätzlich die Möglichkeiten der nichtlinearen THz-Spektroskopie an Magneten.

Представлен обзор современного состояния исследований в области спинтроники и магноники. Рассмотрены основные концепции создания устройств на принципах магнонной логики, а также некоторые эффекты, необходимые для генерации и детектирования магнонных сигналов. Особое внимание уделено возможностям управления магнитной подсистемой с помощью спиновых и электрических токов, механического напряжения, а также повышению рабочих диапазонов частот. Обсуждаются некоторые конкретные реализованные на данный момент компоненты и пути их дальнейшего развития., An overview of the current state of research in the field of spintronics and magnonics is presented. The basic concepts of creating devices based on the principles of magnonic logic are considered, as well as some of the effects required for the generation and detection of magnon signals. Particular attention is paid to the possibilities of controlling the magnetic subsystem by means of spin and electric currents, mechanical strain, as well as increasing the operating frequency ranges. Some specific components implemented so far and the ways of their further development are discussed.

In this communication, we report the results of the studies on structural and transport properties of monovalent Na + doped La1-xNaxMnO3 (LNMO; x = 0.00, 0.05, 0.10, 0.15, 0.20, 0.25 and 0.30) manganites synthesized by conventional ceramic method. X-ray diffraction (XRD) and Rietveld refinements reveal the single phasic nature of LNMO manganites without any detectable impurity within the measurement range. Temperature dependent resistivity, under different applied magnetic fields, has been performed on LNMO samples. Samples understudy exhibit metal to insulator (semiconductor) transition at temperature TP which is strongly influenced by the substitution of Na + at La 3+ site.  - T plots also exhibit resistivity upturn behavior at low temperature well below 40K under all the applied fields. Variation in TP and resistivity has been discussed in the context of the competition between the transport favoring tolerance factor and zener double exchange (ZDE) mechanism and transport degrading Jahn-Teller (JT) and size variance effects. In order to understand the mechanisms responsible for the charge transport in metallic and semiconducting regions and to explore the possible electronic processes responsible for the observed low temperature resistivity minima in all the presently studied LNMO manganites, various models have been employed. It has been found that VRH mechanism gets successfully fitted to the resistivity data in the semiconducting region while ZDE polynomial law is responsible for the charge conduction in metallic region for all the presently studied LNMO samples. A strong dependence of activation energy on the Na + - content as well as applied magnetic field has been discussed in the context of variation and interrelations between the structural parameters. Charge conduction in metallic region has been discussed in the light of electron-phonon interactions which is influenced by the Na + - content and applied magnetic field. Electrostatic blockade model has been employed to understand the low temperature resistivity minima behavior. Blocking energy for the charge carriers shows a dependence on the magnetic energy provided to the charge carriers. Present study can be useful to understand and to control the charge conduction in the manganites and hence to design the manganite based thin film devices for various spintronic applications. Copyright © 2016 VBRI Press.

Stoichiometric Cr2Se3 single crystals are particular layer-structured antiferromagnets, which possess a noncollinear spin configuration, weak ferromagnetic moments, moderate magnetoresistance (MR ∼14.3%), and poor metallic conductivity below the antiferromagnetic phase transition. Here, we report an interesting >16 000% colossal magnetoresistance (CMR) effect in Ti (1.5 atomic percent) lightly doped Cr2Se3 single crystals. Such a CMR is approximately 1143 times larger than that of the stoichiometric Cr2Se3 crystals and is rarely observed in layered antiferromagnets and is attributed to the frustrated spin configuration. Moreover, the Ti doping not only dramatically changes the electronic conductivity of the Cr2Se3 crystal from a bad metal to a semiconductor with a gap of ∼15 meV but also induces a change in the magnetic anisotropy of the Cr2Se3 crystal from strong out-of-plane to weak in-plane. Further, magnetotransport measurements reveal that the low-field MR scales with the square of the reduced magnetization, which is a signature of CMR materials. The layered Ti:Cr2Se3 with the CMR effect could be used as two-dimensional (2D) heterostructure building blocks to provide colossal negative MR in spintronic devices.

The heavy rare-earth GdFeO3-type RFeO3 (R = Dy, Ho and Er) orthoferrites (space group Pnma, N 62) show spin reorientation transition characterized by a turning point on the magnetization curves. The basic Arrott plots curves showing positive slopes confirm the second-order nature of the spin reorientation and the transition temperature TSR is estimated to be ∼45 K, ∼53 K and ∼94 K for DyFeO3, HoFeO3 and ErFeO3, respectively. In addition, magnetic entropy change − Δ S M of the three samples is calculated to be 11.4, 9.8 and 7.4 J kg−1 K−1 at 10 K and 50 kOe, respectively. The field sensitive antiferromagnetic state and competitive magnetocaloric performances in RFeO3 have been attracting considerable interest for the possible applications in spintronic devices.

As the feature sizes of electronic devices continue to shrink, new technologies—in particular spintronics and derived interfacial architectures—become increasingly pivotal. In this context, two-dimensional van der Waals materials and their interfaces are particularly attractive, relying on their ultimate atomic thicknesses and exceptional spin-related properties. This review provides a critical evaluation on the state-of-the-art of van der Waals interfaces and projected technological applications in spintronics, highlights major challenges and a viable solution—an all-in-situ growth and characterization strategy, and finally identifies several emerging spin-based technologies that might significantly benefit from the versatile van der Waals interfaces enabled by the strategy.

Inducing ferromagnetism into graphene is vital today because it has a wide range of applications such as spintronics devices and magnetic memory devices. In this paper, we will report a new method to synthesize ferromagnetic graphene by nitrogen doping. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy were utilized to testify the N-doped material and further discuss the N-doped process. The superconducting quantum interference device (SQUID) was put in and used to analyze the magnetic properties of the N-doped graphene sheets. It shows that the material exhibits ferromagnetism at both 3 K and 300 K and the ferromagnetic saturation moment is 0.412 emu/g and 0.051 emu/g respectively. The mechanism of the origin of the ferromagnetism in N-doped graphene sheets will also be discussed in this paper. It shows that, when the amount graphitic N reached the threshold, the origin of the ferromagnetism will change from defects induced by nitrogen atoms to the transition in energy band caused by graphitic N.

Electric manipulation of magnetization is essential for the integration of magnetic functionalities in integrated circuits. Spin-orbit torque (SOT), originating from the coupling of electron spin and orbital motion through spin-orbital interaction, can effectively manipulate magnetization. Symmetry breaking plays an important role in spintronics based on SOT. SOT requires inversion asymmetry in order to have a net effect on magnetic materials, which is commonly realized by spatial asymmetry: a thin magnetic layer sandwiched between two dissimilar layers. This kind of structure restricts the SOT by mirror and rotational symmetries to have a particular form: an “antidamping-like” component oriented in the film plane even upon reversal of the magnetization direction. Consequently, magnetization perpendicular to the film plane cannot be deterministically switched with pure electric current. To achieve all-electric switching of perpendicular magnetization, it is necessary to break the mirror and rotational symmetries of the sandwiched structure.