The emergence of spin electronics in data storage

Emerging neuromorphic devices

Artificial intelligence (AI) has the ability of revolutionizing our lives and society in a radical way, by enabling machine learning in the industry, business, health, transportation, and many other fields. The ability to recognize objects, faces, and speech, requires, however, exceptional computational power and time, which is conflicting with the current difficulties in transistor scaling due to physical and architectural limitations. As a result, to accelerate the progress of AI, it is necessary to develop materials, devices, and systems that closely mimic the human brain. In this work, we review the current status and challenges on the emerging neuromorphic devices for brain-inspired computing. First, we provide an overview of the memory device technologies which have been proposed for synapse and neuron circuits in neuromorphic systems. Then, we describe the implementation of synaptic learning in the two main types of neural networks, namely the deep neural network and the spiking neural network (SNN). Bio-inspired learning, such as the spike-timing dependent plasticity scheme, is shown to enable unsupervised learning processes which are typical of the human brain. Hardware implementations of SNNs for the recognition of spatial and spatio-temporal patterns are also shown to support the cognitive computation in silico. Finally, we explore the recent advances in reproducing bio-neural processes via device physics, such as insulating-metal transitions, nanoionics drift/diffusion, and magnetization flipping in spintronic devices. By harnessing the device physics in emerging materials, neuromorphic engineering with advanced functionality, higher density and better energy efficiency can be developed.

Electric Field-Tunable Giant Magnetoresistance (GMR) Sensor with Enhanced Linear Range

The operation mechanism of giant magnetoresistance (GMR) sensors relies on the linear response of the magnetization direction to an external magnetic field. Since the magnetic anisotropy of ferromagnetic layers can be manipulated by a strain-mediated magnetoelectric coupling effect, we propose a tunable GMR magnetic field sensor design that allows for voltage tuning of the linear range and sensitivity. A spin valve structure Ru/CoFe/Cu/CoFe/IrMn/Ru is grown on a PMN-PT (011) substrate, and the magnetization directions of ferromagnetic layers can be controlled by an electric field. An adjustable linear magnetoresistance is therefore induced. Based on the magnetoelectric coupling effect and spin valve, we prepared tunable GMR magnetic field sensors with bridge structures. The linear sensing range of a DC magnetic field is enhanced 6 times by applying an electric field of 14 kV/cm. The electrically tunable GMR sensor fulfills the requirements to work at different magnetic field ranges in the same configuration, therefore exhibiting great potential for applications in the Internet of things.

Coupling of pinned magnetic moments in an antiferromagnet to a ferromagnet and its role for exchange bias

The interaction between uncompensated pinned magnetic moments within an antiferromagnetic (AFM) layer and an adjacent ferromagnetic (FM) layer responsible for the existence of exchange bias is explored in epitaxially grown trilayers of the form FM2/AFM/FM1 on Cu₃Au(0 0 1) where FM1 is ~12 atomic monolayers (ML) Ni, FM2 is 21-25 ML Ni, and AFM is 27 ML or 50 ML Ni_~25Mn_~75. Field cooling for parallel or antiparallel alignment of the out-of-plane magnetizations of the two FM layers does not make a difference for the temperature-dependent coercivity (H _C), magnitude of exchange bias field (H _eb), AFM ordering temperature (T _AFM), and blocking temperature for exchange bias (T _b). We explain this by a model in which the uncompensated pinned magnetic moments distributed within the volume of the AFM layer interact with both of the FM layers, albeit with different strength. Parallel and antiparallel coupling between the magnetization of the pinned moments and the FM layers equally exists. This leads to the experimentally observed independence of H _C, H _eb, as well as of T _AFM and T _b on the magnetization direction of the FM layers during field cooling. These results provide new and detailed insight into revealing the subtle and complex nature of the exchange bias effect.

Electrical switching in a magnetically intercalated transition metal dichalcogenide

Advances in controlling the correlated behaviour of transition metal dichalcogenides have opened a new frontier of many-body physics in two dimensions. A field where these materials have yet to make a deep impact is antiferromagnetic spintronics-a relatively new research direction promising technologies with fast switching times, insensitivity to magnetic perturbations and reduced cross-talk^1-3. Here, we present measurements on the intercalated transition metal dichalcogenide Fe_1/3NbS₂ that exhibits antiferromagnetic ordering below 42 K (refs. ^4,5). We find that remarkably low current densities of the order of 10⁴ A cm^-2 can reorient the magnetic order, which can be detected through changes in the sample resistance, demonstrating its use as an electronically accessible antiferromagnetic switch. Fe_1/3NbS₂ is part of a larger family of magnetically intercalated transition metal dichalcogenides, some of which may exhibit switching at room temperature, forming a platform from which to build tuneable antiferromagnetic spintronic devices^6,7.

Observation of Large Unidirectional Rashba Magnetoresistance in Ge(111)

Relating magnetotransport properties to specific spin textures at surfaces or interfaces is an intense field of research nowadays. Here, we investigate the variation of the electrical resistance of Ge(111) grown epitaxially on semi-insulating Si(111) under the application of an external magnetic field. We find a magnetoresistance term that is linear in current density j and magnetic field B, hence, odd in j and B, corresponding to a unidirectional magnetoresistance. At 15 K, for I=10  μA (or j=0.33  A m^{-1}) and B=1  T, it represents 0.5% of the zero field resistance, a much higher value compared to previous reports on unidirectional magnetoresistance (UMR). We ascribe the origin of this magnetoresistance to the interplay between the externally applied magnetic field and the pseudomagnetic field generated by the current applied in the spin-splitted subsurface states of Ge(111). This unidirectional magnetoresistance is independent of the current direction with respect to the Ge crystal axes. It progressively vanishes, either using a negative gate voltage due to carrier activation into the bulk (without spin-splitted bands), or by increasing the temperature due to the Rashba energy splitting of the subsurface states lower than ∼58k_{B}. We believe that UMR could be used as a powerful probe of the spin-orbit interaction in a wide range of materials.

Current-Induced Helicity Reversal of a Single Skyrmionic Bubble Chain in a Nanostructured Frustrated Magnet

Helicity indicates the in-plane magnetic-moment swirling direction of a skyrmionic configuration. The ability to reverse the helicity of a skyrmionic bubble via purely electrical means has been predicted in frustrated magnetic systems; however, it has been challenging to observe this experimentally. The current-driven helicity reversal of the skyrmionic bubble in a nanostructured frustrated Fe₃ Sn₂ magnet is experimentally demonstrated. The critical current density required to trigger the helicity reversal is 10⁹ -10¹⁰ A m^-2 , with a corresponding pulse-width varying from 1 µs to 100 ns. Computational simulations reveal that both the pinning effect and dipole-dipole interaction play a crucial role in the helicity reversal process.

Memristive and CMOS Devices for Neuromorphic Computing

Neuromorphic computing has emerged as one of the most promising paradigms to overcome the limitations of von Neumann architecture of conventional digital processors. The aim of neuromorphic computing is to faithfully reproduce the computing processes in the human brain, thus paralleling its outstanding energy efficiency and compactness. Toward this goal, however, some major challenges have to be faced. Since the brain processes information by high-density neural networks with ultra-low power consumption, novel device concepts combining high scalability, low-power operation, and advanced computing functionality must be developed. This work provides an overview of the most promising device concepts in neuromorphic computing including complementary metal-oxide semiconductor (CMOS) and memristive technologies. First, the physics and operation of CMOS-based floating-gate memory devices in artificial neural networks will be addressed. Then, several memristive concepts will be reviewed and discussed for applications in deep neural network and spiking neural network architectures. Finally, the main technology challenges and perspectives of neuromorphic computing will be discussed.

Band-Structure Spin-Filtering in Vertical Spin Valves Based on Chemical Vapor Deposited WS2

We report on spin transport in WS₂-based 2D-magnetic tunnel junctions (2D-MTJs), unveiling a band structure spin filtering effect specific to the transition metal dichalcogenides (TMDCs) family. WS₂ mono-, bi-, and trilayers are derived by a chemical vapor deposition process and further characterized by Raman spectroscopy, atomic force microscopy (AFM), and photoluminescence spectroscopy. The WS₂ layers are then integrated in complete Co/Al₂O₃/WS₂/Co MTJ hybrid spin-valve structures. We make use of a tunnel Co/Al₂O₃ spin analyzer to probe the extracted spin-polarized current from the WS₂/Co interface and its evolution as a function of WS₂ layer thicknesses. For monolayer WS₂, our technological approach enables the extraction of the largest spin signal reported for a TMDC-based spin valve, corresponding to a spin polarization of P_Co/WS2 = 12%. Interestingly, for bi- and trilayer WS₂, the spin signal is reversed, which indicates a switch in the mechanism of interfacial spin extraction. With the support of ab initio calculations, we propose a model to address the experimentally measured inversion of the spin polarization based on the change in the WS₂ band structure while going from monolayer (direct bandgap) to bilayer (indirect bandgap). These experiments illustrate the rich potential of the families of semiconducting 2D materials for the control of spin currents in 2D-MTJs.

Magnetic Tunnel Junction Applications

Spin-based devices can reduce energy leakage and thus increase energy efficiency. They have been seen as an approach to overcoming the constraints of CMOS downscaling, specifically, the Magnetic Tunnel Junction (MTJ) which has been the focus of much research in recent years. Its nonvolatility, scalability and low power consumption are highly attractive when applied in several components. This paper aims at providing a survey of a selection of MTJ applications such as memory and analog to digital converter, among others.

High Volume-Per-Dose and Low Resistivity of Cobalt Nanowires Grown by Ga+ Focused Ion Beam Induced Deposition

The growth of ferromagnetic nanostructures by means of focused-Ga+-beam-induced deposition (Ga+-FIBID) using the Co2(CO)8 precursor has been systematically investigated. The work aimed to obtain growth conditions allowing for the simultaneous occurrence of high growth speed, good lateral resolution, low electrical resistivity, and ferromagnetic behavior. As a first result, it has been found that the competition between deposition and milling that is produced by the Ga+ beam is a limiting factor. In our working conditions, with the maximum available precursor flux, the maximum deposit thickness has been found to be 65 nm. The obtained volumetric growth rate is at least 50 times higher than in the case of deposition by focused-electron-beam-induced deposition. The lateral resolution of the deposits can be as good as 50 nm while using Ga+-beam currents lower than 10 pA. The high metallic content of the as-grown deposits gives rise to a low electrical resistivity, within the range 20-40 µΩ·cm. Magnetic measurements confirm the ferromagnetic nature of the deposits at room temperature. In conclusion, the set of obtained results indicates that the growth of functional ferromagnetic nanostructures by Ga+-FIBID while using the Co2(CO)8 precursor is a viable and competitive technique when compared to related nanofabrication techniques.

Full voltage manipulation of the resistance of a magnetic tunnel junction

One of the motivations for multiferroics research is to find an energy-efficient solution to spintronic applications, such as the solely electrical control of magnetic tunnel junctions. Here, we integrate spintronics and multiferroics by depositing MgO-based magnetic tunnel junctions on ferroelectric substrate. We fabricate two pairs of electrodes on the ferroelectric substrate to generate localized strain by applying voltage. This voltage-generated localized strain has the ability to modify the magnetic anisotropy of the free layer effectively. By sequentially applying voltages to these two pairs of electrodes, we successively and unidirectionally rotate the magnetization of the free layer in the magnetic tunnel junctions to complete reversible 180° magnetization switching. Thus, we accomplish a giant nonvolatile solely electrical switchable high/low resistance in magnetic tunnel junctions at room temperature without the aid of a magnetic field. Our results are important for exploring voltage control of magnetism and low-power spintronic devices.

Glassy Magnetic Behavior and Correlation Length in Nanogranular Fe-Oxide and Au/Fe-Oxide Samples

In nanoscale magnetic systems, the possible coexistence of structural disorder and competing magnetic interactions may determine the appearance of a glassy magnetic behavior, implying the onset of a low-temperature disordered collective state of frozen magnetic moments. This phenomenology is the object of an intense research activity, stimulated by a fundamental scientific interest and by the need to clarify how disordered magnetism effects may affect the performance of magnetic devices (e.g., sensors and data storage media). We report the results of a magnetic study that aims to broaden the basic knowledge of glassy magnetic systems and concerns the comparison between two samples, prepared by a polyol method. The first can be described as a nanogranular spinel Fe-oxide phase composed of ultrafine nanocrystallites (size of the order of 1 nm); in the second, the Fe-oxide phase incorporated non-magnetic Au nanoparticles (10-20 nm in size). In both samples, the Fe-oxide phase exhibits a glassy magnetic behavior and the nanocrystallite moments undergo a very similar freezing process. However, in the frozen regime, the Au/Fe-oxide composite sample is magnetically softer. This effect is explained by considering that the Au nanoparticles constitute physical constraints that limit the length of magnetic correlation between the frozen Fe-oxide moments.

Impact of single atomic defects and vacancies on the magnetic anisotropy energy of CoPt thin films

The impact of surface vacancies and single adatoms on the magnetic properties of tetragonal L1 ₀ CoPt thin films is investigated from first principles. We consider Co and Fe single adatoms deposited on a Pt-terminated thin film while a Pt adatom is assumed to be supported by a Co-terminated film. The vacancy is injected in the top-surface layer of the films with both types of termination. After finding the most stable location of the defects, we discuss their magnetic properties tied to those of the substrate and investigate the magnetocrystalline anisotropy energy (MAE). Previous simulations (Brahimi et al 2016 J. Phys.: Condens. Matter 28 496002) predicted a large out-of-plane surface MAE for the Pt-terminated CoPt films (4 meV per f.u.) in contrast to in-plane surface MAE for Co-terminated films (-1 meV per f.u.). Here, we find that the surface MAE is significantly modified upon the presence of the atomic defects. All investigated defects induce an in-plane MAE, which is large enough for Fe adatom and Pt vacancy to switch the surface MAE from out-of-plane to in-plane for the Pt-terminated films. Interestingly, among the investigated defects Pt vacancy has the largest effect on the MAE in contrast to Co vacancy, which induced the smallest but still significant effect. This behavior is explained in terms of the orbital moment anisotropy of the thin films.

Multiscale Modeling for Application-Oriented Optimization of Resistive Random-Access Memory

Memristor-based neuromorphic systems have been proposed as a promising alternative to von Neumann computing architectures, which are currently challenged by the ever-increasing computational power required by modern artificial intelligence (AI) algorithms. The design and optimization of memristive devices for specific AI applications is thus of paramount importance, but still extremely complex, as many different physical mechanisms and their interactions have to be accounted for, which are, in many cases, not fully understood. The high complexity of the physical mechanisms involved and their partial comprehension are currently hampering the development of memristive devices and preventing their optimization. In this work, we tackle the application-oriented optimization of Resistive Random-Access Memory (RRAM) devices using a multiscale modeling platform. The considered platform includes all the involved physical mechanisms (i.e., charge transport and trapping, and ion generation, diffusion, and recombination) and accounts for the 3D electric and temperature field in the device. Thanks to its multiscale nature, the modeling platform allows RRAM devices to be simulated and the microscopic physical mechanisms involved to be investigated, the device performance to be connected to the material’s microscopic properties and geometries, the device electrical characteristics to be predicted, the effect of the forming conditions (i.e., temperature, compliance current, and voltage stress) on the device’s performance and variability to be evaluated, the analog resistance switching to be optimized, and the device’s reliability and failure causes to be investigated. The discussion of the presented simulation results provides useful insights for supporting the application-oriented optimization of RRAM technology according to specific AI applications, for the implementation of either non-volatile memories, deep neural networks, or spiking neural networks.

Realizing Room-Temperature Resonant Tunnel Magnetoresistance in Cr/Fe/MgAl2O4 Quasi-Quantum Well Structures

The quantum well (QW) realizes new functionalities due to the discrete electronic energy levels formed in the well-shaped potential. Magnetic tunnel junctions (MTJs) combined with a quasi-QW structure of Cr/ultrathin-Fe/MgAl2O4(001)/Fe, in which the Cr quasi-barrier layer confines Δ 1 up-spin electrons to the Fe well, are prepared with perfectly lattice-matched interfaces and atomic layer number control. Resonant peaks are clearly observed in the differential conductance of the MTJs due to the formation of QWs. Furthermore, enhanced tunnel magnetoresistance (TMR) peaks at the resonant bias voltages are realized for the MTJs at room temperature, i.e., it is observed that TMR ratios at specific and even high bias-voltages (V bias) are larger than zero-bias TMR ratios for the MTJs with odd Fe atomic layers, in contrast to the earlier experimental studies. In addition, a new finding in this study is unique sign changes in the temperature coefficient of resistance (TCR) depending on the Fe thickness and V bias, which is interpreted as a signature of the QW formation of Δ1 symmetry electronic states. The present study suggests that the spin-dependent resonant tunneling via the QWs formed in Cr/ultrathin-Fe/MgAl2O4/Fe structures should open a new pathway to achieve a large TMR at practically high V bias.

Polarization Control of the Interface Ferromagnetic to Antiferromagnetic Phase Transition in Co/Pb(Zr,Ti)O3

Based on first-principles calculations, we predict the polarization control of the interfacial magnetic phase and a giant electronically driven magnetoelectric coupling (MEC) in Co/PbZr_0.25Ti_0.75O₃ (PZT)(001). The effect of Co oxidation at the interface shared with (Zr,Ti)O₂-terminated PZT is evidenced. The magnetic phase of the oxidized Co interface layer is electrically switched from the ferromagnetic to the antiferromagnetic state by reversing the PZT polarization from upward to downward, respectively. A comparative study between oxidized and unoxidized Co/PZT interfaces shows that in oxidized Co/PZT bilayers, the variation of the interface spin moment upon polarization reversal exceeds that of unoxidized Co/PZT bilayers by about 1 order of magnitude. We define a surface MEC constant α_S taking into account the polarization dependence of both the spin and orbital moments. In unoxidized Co/PZT bilayers, we obtain α_S ≈ 2 × 10^-10 G cm² V^-1, while a giant surface coupling α_S ≈ 12 × 10^-10 G cm² V^-1 is found in the case of oxidized Co/PZT. We demonstrate that the polarization control of the magnetocrystalline anisotropy via spin-orbit coupling is not only effective at the interface but it extends to the Co film despite the interface origin of the MEC. This study shows that tailoring the nature of atomic bonding and electron occupancies allows for improving the performance of functional interfaces, enabling an efficient electric field control of spin-orbit interactions. Moreover, the nonlocal character of this effect holds promising perspectives for the application of electronically driven interface MEC in spin-orbitronic devices.

Achieving large and nonvolatile tunable magnetoresistance in organic spin valves using electronic phase separated manganites

Tailoring molecular spinterface between novel magnetic materials and organic semiconductors offers promise to achieve high spin injection efficiency. Yet it has been challenging to achieve simultaneously a high and nonvolatile control of magnetoresistance effect in organic spintronic devices. To date, the largest magnetoresistance (~300% at T = 10 K) has been reached in tris-(8-hydroxyquinoline) aluminum (Alq₃)-based organic spin valves (OSVs) using La_0.67Sr_0.33MnO₃ as a magnetic electrode. Here we demonstrate that one type of perovskite manganites, i.e., a (La_2/3Pr_1/3)_5/8Ca_3/8MnO₃ thin film with pronounced electronic phase separation (EPS), can be used in Alq₃-based OSVs to achieve a large magnetoresistance (MR) up to 440% at T = 10 K and a typical electrical Hanle effect as the Hallmark of the spin injection. The contactless magnetic field-controlled EPS enables us to achieve a nonvolatile tunable MR response persisting up to 120 K. Our study suggests a new route to design high performance multifunctional OSV devices using electronic phase separated manganites.

Organic materials hold great potential of for spintronic applications. Here the authors show electronic phase dependent magnetoresistance (MR) effect in LPCMO/Alq₃/Co junctions with large MR up to 440% at 10 K as well as electrical Hanle effect as the Hallmark of the spin injection.

Tetrahedral chain ordering and low dimensional magnetic lattice in a new brownmillerite Sr2ScFeO5

We report the synthesis, structure and physical properties of a hitherto unreported brownmillerite compound Sr2ScFeO5. We have shown a new ordering sequence of the interlayer iron tetrahedral chains. Reduced dimensionality of the magnetic lattice and the frustration in the two dimensional iron tetrahedral chains originate complex magnetic and magneto-dielectric effects. Our study highlights a novel approach to tailor the magnetic lattice in bulk oxides.

Free Field Electric Switching of Perpendicularly Magnetized Thin Film by Spin Current Gradient

To realize high-speed nonvolatile magnetic memory with low energy consumption, electric switching of perpendicular magnetization by spin-orbit torque in the heavy metal/ferromagnetic (HM/FM) structure has recently attracted intensive attention. Conventionally, an external in-plane magnetic field for breaking the symmetry is required for achieving electric switching of perpendicular magnetization. However, electric switching without external field is the prerequisite for the integration of magnetic functionality into the integrated circuit devices. Here, we propose a new method of utilizing a W wedge in the Pt/W/FM structure to induce a spin current gradient, which can result in an in-plane equivalent field along the wedge thickness gradient direction. We experimentally demonstrate the deterministic magnetization switching of perpendicular Co/Ni multilayers without external magnetic field when the electric current is along the wedge thickness gradient direction. Our findings shed light on free field electric switching of magnetization by a new physical parameter-an asymmetric spin current induced by a bilayer wedge structure.

Electrically driven spin torque and dynamical Dzyaloshinskii-Moriya interaction in magnetic bilayer systems

Efficient control of magnetism with electric means is a central issue of current spintronics research, which opens an opportunity to design integrated spintronic devices. However, recent well-studied methods are mostly based on electric-current injection, and they are inevitably accompanied by considerable energy losses through Joule heating. Here we theoretically propose a way to exert spin torques into magnetic bilayer systems by application of electric voltages through taking advantage of the Rashba spin-orbit interaction. The torques resemble the well-known electric-current-induced torques, providing similar controllability of magnetism but without Joule-heating energy losses. The torques also turn out to work as an interfacial Dzyaloshinskii-Moriya interaction which enables us to activate and create noncollinear magnetism like skyrmions by electric-voltage application. Our proposal offers an efficient technique to manipulate magnetizations in spintronics devices without Joule-heating energy losses.

Room-temperature Operation of Low-voltage, Non-volatile, Compound-semiconductor Memory Cells

Whilst the different forms of conventional (charge-based) memories are well suited to their individual roles in computers and other electronic devices, flaws in their properties mean that intensive research into alternative, or emerging, memories continues. In particular, the goal of simultaneously achieving the contradictory requirements of non-volatility and fast, low-voltage (low-energy) switching has proved challenging. Here, we report an oxide-free, floating-gate memory cell based on III-V semiconductor heterostructures with a junctionless channel and non-destructive read of the stored data. Non-volatile data retention of at least 10⁴ s in combination with switching at ≤2.6 V is achieved by use of the extraordinary 2.1 eV conduction band offsets of InAs/AlSb and a triple-barrier resonant tunnelling structure. The combination of low-voltage operation and small capacitance implies intrinsic switching energy per unit area that is 100 and 1000 times smaller than dynamic random access memory and Flash respectively. The device may thus be considered as a new emerging memory with considerable potential.

Exchange-biased hybrid γ-Fe2O3/NiO core-shell nanostructures: three-step synthesis, microstructure, and magnetic properties

A two-step solvothermal method combining a calcination process was conducted to synthesize γ-Fe2O3/NiO core-shell nanostructures with controlled microstructure. The formation mechanism of this binary system has been discussed, and the influence of microstructures on magnetic properties has been analyzed in detail. Microstructural characterizations reveal that the NiO shells consisted of many irregular nanosheets with disordered orientations and monocrystalline structures, packed on the surface of the γ-Fe2O3 microspheres. Both the grain size and NiO content of nanostructures increase with the increasing calcination temperature from 300 °C to 400 °C, accompanied by an enhancement of the compactness of NiO shells. Magnetic studies indicate that their magnetic properties are determined by four factors: the size effect, NiO phase content, interface microstructure, i.e. contact mode, area, roughness and compactness, and FM-AFM (where FM and AFM denote the ferromagnetic γ-Fe2O3 and the antiferromagnetic NiO components, respectively) coupling effect. At 5 K, the γ-Fe2O3/NiO core-shell nanostructures display certain exchange bias (HE = 60 Oe) and enhanced coercivity (HC = 213 Oe).

Charge Disproportionation Triggers Bipolar Doping in FeSb2- xSn xSe4 Ferromagnetic Semiconductors, Enabling a Temperature-Induced Lifshitz Transition

Ferromagnetic semiconductors (FMSs) featuring a high Curie transition temperature ( T_c) and a strong correlation between itinerant carriers and localized magnetic moments are of tremendous importance for the development of practical spintronic devices. The realization of such materials hinges on the ability to generate and manipulate a high density of itinerant spin-polarized carriers and the understanding of their responses to external stimuli. In this study, we demonstrate the ability to tune magnetic ordering in the p-type FMS FeSb_{2- x}Sn _xSe₄ (0 ≤ x ≤ 0.20) through carrier density engineering. We found that the substitution of Sb by Sn FeSb_{2- x}Sn _xSe₄ increases the ordering of metal atoms within the selenium crystal lattice, leading to a large separation between magnetic centers. This results in a decrease in the T_c from 450 K for samples with x ≤ 0.05 to 325 K for samples with 0.05 < x ≤ 0.2. In addition, charge disproportionation arising from the substitution of Sb³⁺ by Sn²⁺ triggers the partial oxidation of Sb³⁺ to Sb⁵⁺, which is accompanied by the generation of both electrons and holes. This leads to a drastic decrease in the electrical resistivity and thermopower simultaneously with a large increase in the magnetic susceptibility and saturation magnetization upon increasing Sn content. The observed bipolar doping induces a very interesting temperature-induced quantum electronic transition (Lifshitz transition), which is manifested by the presence of an anomalous peak in the resistivity curve simultaneously with a reversal of the sign of a majority of the charge carriers from hole-like to electron-like at the temperature of maximum resistivity. This study suggests that while there is a strong correlation between the overall magnetic moment and free carrier spin in FeSb_{2- x}Sn _xSe₄ FMSs, the magnitude of the Curie temperature strongly depends on the spatial separation between localized magnetic centers rather than the concentration of magnetic atoms or the density of itinerant carriers.

Giant anisotropic magnetoresistance and nonvolatile memory in canted antiferromagnet Sr2IrO4

Antiferromagnets have been generating intense interest in the spintronics community, owing to their intrinsic appealing properties like zero stray field and ultrafast spin dynamics. While the control of antiferromagnetic (AFM) orders has been realized by various means, applicably appreciated functionalities on the readout side of AFM-based devices are urgently desired. Here, we report the remarkably enhanced anisotropic magnetoresistance (AMR) as giant as ~160% in a simple resistor structure made of AFM Sr₂IrO₄ without auxiliary reference layer. The underlying mechanism for the giant AMR is an indispensable combination of atomic scale giant-MR-like effect and magnetocrystalline anisotropy energy, which was not accessed earlier. Furthermore, we demonstrate the bistable nonvolatile memory states that can be switched in-situ without the inconvenient heat-assisted procedure, and robustly preserved even at zero magnetic field, due to the modified interlayer coupling by 1% Ga-doping in Sr₂IrO₄. These findings represent a straightforward step toward the AFM spintronic devices.

Voltage-Controlled Magnetic Anisotropy MeRAM Bit-Cell over Event Transient Effects

Magnetic tunnel junction (MTJ) with a voltage-controlled magnetic anisotropy (VCMA) effect has been introduced to achieve robust non-volatile writing control with an electric field or a switching voltage. However, continuous technology scaling down makes circuits more susceptible to temporary faults. The reliability of VCMA-MTJ-based magnetoelectric random access memory (MeRAM) can be impacted by environmental disturbances because a radiation strike on the access transistor could introduce write and read failures in 1T-1MTJ MeRAM bit-cells. In this work, Single-Event Transient (SET) effects on a VCMA-MTJ-based MeRAM in 28 nm FDSOI CMOS technology are investigated. Results show the minimum SET charge Q c required to reach the access transistor associated with the striking time that can lead to an unsuccessful switch, that is, an error in the writing process (write failure). The synchronism between the fluctuations of the magnetic field in the MTJ free layer and the moment of the write pulse is also analyzed in terms of SET robustness. Moreover, results show that the minimum Q c value can vary more than 100 % depending on the magnetic state of the MTJ and the width of the access transistor. In addition, the most critical time against the SET occurrence may be before or after the write pulse depending on the magnetic state of the MTJ.

Strong magnetoelectric coupling in mixed ferrimagnetic-multiferroic phases of a double perovskite

Exploring new magnetic materials is essential for finding advantageous functional properties such as magnetoresistance, magnetocaloric effect, spintronic functionality, and multiferroicity. Versatile classes of double perovskite compounds have been recently investigated because of intriguing physical properties arising from the proper combination of several magnetic ions. In this study, it is observed that the dominant ferrimagnetic phase is coexisted with a minor multiferroic phase in single-crystalline double-perovskite Er₂CoMnO₆. The majority portion of the ferrimagnetic order is activated by the long-range order of Er³⁺ moments below T_Er = 10 K in addition to the ferromagnetic order of Co²⁺ and Mn⁴⁺ moments arising at T_C = 67 K, characterized by compensated magnetization at T_Comp = 3.15 K. The inverted magnetic hysteresis loop observed below T_Comp can be described by an extended Stoner-Wohlfarth model. The additional multiferroic phase is identified by the ferroelectric polarization of ~0.9 μC/m² at 2 K. The coexisting ferrimagnetic and multiferroic phases appear to be strongly correlated in that metamagnetic and ferroelectric transitions occur simultaneously. The results based on intricate magnetic correlations and phases in Er₂CoMnO₆ enrich fundamental and applied research on magnetic materials through the scope of distinct magnetic characteristics in double perovskites.

Electrically Switchable and Tunable Rashba-Type Spin Splitting in Covalent Perovskite Oxides

In transition-metal perovskites (ABO_{3}) most physical properties are tunable by structural parameters such as the rotation of the BO_{6} octahedra. Examples include the Néel temperature of orthoferrites, the conductivity of mixed-valence manganites, or the band gap of rare-earth scandates. Since oxides often hold large internal electric dipoles and can accommodate heavy elements, they also emerge as prime candidates to display Rashba spin-orbit coupling, through which charge and spin currents may be efficiently interconverted. However, despite a few experimental reports in SrTiO_{3}-based interface systems, the Rashba interaction has been little studied in these materials, and its interplay with structural distortions remains unknown. In this Letter, we identify a bismuth-based perovskite with a large, electrically switchable Rashba interaction whose amplitude can be controlled by both the ferroelectric polarization and the breathing mode of oxygen octahedra. This particular structural parameter arises from the strongly covalent nature of the Bi-O bonds, reminiscent of the situation in perovskite nickelates. Our results not only provide novel strategies to craft agile spin-charge converters but also highlight the relevance of covalence as a powerful handle to design emerging properties in complex oxides.

Elaboration of Nanomagnet Arrays: Organization and Magnetic Properties of Mass-Selected FePt Nanoparticles Deposited on Epitaxially Grown Graphene on Ir(111)

The moiré pattern created by the epitaxy of a graphene sheet on an iridium substrate can be used as a template for the growth of 2D atomic or cluster arrays. We observed for the first time a coherent organization of hard magnetic preformed FePt nanoparticles on the 2D lattice of graphene on Ir(111). Nanoparticles of 2 nm diameter have been mass selected in a gas phase and deposited with low energy on the hexagonal moiré pattern. Their morphology and organization have been investigated using grazing incidence small angle x-ray scattering, while their magnetic properties have been studied by x-ray magnetic circular dichroism, both pointing to a FePt cluster-graphene surface specific interaction. The spatial coherence of the nanoparticles is preserved upon annealing up to 700 °C where the hard magnetic phase of FePt is obtained.

Solving matrix equations in one step with cross-point resistive arrays

Conventional digital computers can execute advanced operations by a sequence of elementary Boolean functions of 2 or more bits. As a result, complicated tasks such as solving a linear system or solving a differential equation require a large number of computing steps and an extensive use of memory units to store individual bits. To accelerate the execution of such advanced tasks, in-memory computing with resistive memories provides a promising avenue, thanks to analog data storage and physical computation in the memory. Here, we show that a cross-point array of resistive memory devices can directly solve a system of linear equations, or find the matrix eigenvectors. These operations are completed in just one single step, thanks to the physical computing with Ohm's and Kirchhoff's laws, and thanks to the negative feedback connection in the cross-point circuit. Algebraic problems are demonstrated in hardware and applied to classical computing tasks, such as ranking webpages and solving the Schrödinger equation in one step.

The Pathway to Intelligence: Using Stimuli-Responsive Materials as Building Blocks for Constructing Smart and Functional Systems

Systems that are intelligent have the ability to sense their surroundings, analyze, and respond accordingly. In nature, many biological systems are considered intelligent (e.g., humans, animals, and cells). For man-made systems, artificial intelligence is achieved by massively sophisticated electronic machines (e.g., computers and robots operated by advanced algorithms). On the other hand, freestanding materials (i.e., not tethered to a power supply) are usually passive and static. Hence, herein, the question is asked: can materials be fabricated so that they are intelligent? One promising approach is to use stimuli-responsive materials; these "smart" materials use the energy supplied by a stimulus available from the surrounding for performing a corresponding action. After decades of research, many interesting stimuli-responsive materials that can sense and perform smart functions have been developed. Classes of functions discussed include practical functions (e.g., targeting and motion), regulatory functions (e.g., self-regulation and amplification), and analytical processing functions (e.g., memory and computing). The pathway toward creating truly intelligent materials can involve incorporating a combination of these different types of functions into a single integrated system by using stimuli-responsive materials as the basic building blocks.

Disclosing odd symmetry, strain driven magnetic response of Co on Pt/PMN-PT (0 1 1)

An odd-symmetry magnetic response of multiferroic composites comprising ultrathin Co layers on Pt electrodes on [Pb(Mg_0.33Nb_0.67)O₃]_(1-x)[PbTiO₃] _x (PMN-PT) (0 1 1) piezoelectric substrates is observed upon electrical poling of the PMN-PT substrates: the magnetic easy axis of the Co rotates by 90° in-plane between oppositely poled ferroelectric states, mimicking the signature of a surface polarization charge driven effect, which however can be excluded from the presence of the thick Pt interlayer. The origin for this unexpected behavior is as an odd symmetry piezoelectric response of the PMN-PT substrate, as indicated by x-ray diffraction with applied poling, in combination with conventional magnetoelastic coupling. Ferroelectric characterization reveals corresponding features, possibly related to an unswitchable polarization component.

New mechanism of plasmons specific for spin-polarized nanoparticles

Here it is experimentally shown that Co nanoparticles with a single-domain crystal structure support a plasmon resonance at approximately 280 nm with better quality than gold nanoparticle resonance in the visible. Magnetic nature of the nanoparticles suggests a new type of these plasmons. The exchange interaction of electrons splits the energy bands between spin-up electrons and spin-down electrons. It makes it possible for coexistence of two independent channels of conductivity as well as two independent plasmons in the same nanoparticle with very different electron relaxation. Indeed, the density of empty states in a partially populated d-band is high, resulting in a large relaxation rate of the spin-down conduction electrons and consequently in low quality of the plasmon resonance. In contrast, the majority electrons with a completely filled d-band do not provide final states for the scattering processes of the conduction spin-up electrons, therefore supporting a high quality plasmon resonance. The scattering without spin flip is required to keep these two plasmons independent.

Micro-Area Ferroelectric, Piezoelectric and Conductive Properties of Single BiFeO₃ Nanowire by Scanning Probe Microscopy

Ferroelectric nanowires have attracted great attention due to their excellent physical properties. We report the domain structure, ferroelectric, piezoelectric, and conductive properties of bismuth ferrite (BFO, short for BiFeO₃) nanowires characterized by scanning probe microscopy (SPM). The X-ray diffraction (XRD) pattern presents single phase BFO without other obvious impurities. The piezoresponse force microscopy (PFM) results indicate that the nanowires possess a multidomain configuration, and the maximum piezoelectric coefficient (d₃₃) of single BFO nanowire is 22.21 pm/V. Poling experiments and local switching spectroscopy piezoresponse force microscopy (SS-PFM) demonstrate that there is sufficient polarization switching behavior and obvious piezoelectric properties in BFO nanowires. The conducting atomic force microscopy (C-AFM) results show that the current is just hundreds of pA at 8 V. These lay the foundation for the application of BFO nanowires in nanodevices.

Molecular multifunctionality preservation upon surface deposition for a chiral single-molecule magnet

Simultaneous retention of SMM behaviour and of optical activity is demonstrated upon surface deposition for a chiral SMM.

The synthesis and characterization of a chiral, enneanuclear Mn(iii)-based, Single-Molecule Magnet, [Mn₉O₄(Me-sao)₆(L)₃(MeO)₃(MeOH)₃]Cl (1; Me-saoH₂ = methylsalicylaldoxime, HL = lipoic acid) is reported. Compound 1 crystallizes in the orthorhombic P2₁2₁2₁ space group and consists of a metallic skeleton describing a defect super-tetrahedron missing one vertex. The chirality of the [Mn^III₉] core originates from the directional bridging of the Me-sao^2– ligands via the –N–O– oximate moieties, which define a clockwise (1ΔΔ) or counter-clockwise (1ΛΛ) rotation in both the upper [Mn^III₃] and lower [Mn^III₆] subunits. Structural integrity and retention of chirality upon dissolution and upon deposition on (a) gold nanoparticles, 1@AuNPs, (b) transparent Au(111) surfaces, 1ΛΛ@t-Au(111); 1ΔΔ@t-Au(111), and (c) epitaxial Au(111) on mica surfaces, 1@e-Au(111), was confirmed by CD and IR spectroscopies, mass spectrometry, TEM, XPS, XAS, and AFM. Magnetic susceptibility and magnetization measurements demonstrate the simultaneous retention of SMM behaviour and optical activity, from the solid state, via dissolution, to the surface deposited species.

Improvement of the performance in Cr-doped ZnO memory devices via control of oxygen defects

The defect-enhanced resistive switching behavior of Cr-doped ZnO films was investigated in this study, and evidence that the switching effect can be attributed to defects was found. X-ray photoelectron spectroscopy demonstrated the existence of oxygen vacancies in the ZnO-based films, and the concentration of oxygen vacancies in the Cr-doped ZnO film was larger than that in the undoped ZnO film, which can be attributed to Cr doping. We concluded that the defects in Cr-doped ZnO were due to the Cr dopant, leading to excellent performance of Cr-doped ZnO films. In particular, depth-profiling analysis of the X-ray photoelectron spectra demonstrated that the resistive switching effects corresponded to variations in the concentration of the defects. The results confirmed that oxygen vacancies are crucial for the entire class of resistive switching effects in Cr-doped ZnO films. In particular, the Cr-doped ZnO films not only show bipolar resistive switching behavior but also excellent reliability and stability, which should be beneficial for next-generation memory device applications.

Giant nonvolatile manipulation of magnetoresistance in magnetic tunnel junctions by electric fields via magnetoelectric coupling

Electrically switchable magnetization is considered a milestone in the development of ultralow power spintronic devices, and it has been a long sought-after goal for electric-field control of magnetoresistance in magnetic tunnel junctions with ultralow power consumption. Here, through integrating spintronics and multiferroics, we investigate MgO-based magnetic tunnel junctions on ferroelectric substrate with a high tunnel magnetoresistance ratio of 235%. A giant, reversible and nonvolatile electric-field manipulation of magnetoresistance to about 55% is realized at room temperature without the assistance of a magnetic field. Through strain-mediated magnetoelectric coupling, the electric field modifies the magnetic anisotropy of the free layer leading to its magnetization rotation so that the relative magnetization configuration of the magnetic tunnel junction can be efficiently modulated. Our findings offer significant fundamental insight into information storage using electric writing and magnetic reading and represent a crucial step towards low-power spintronic devices.

High-Magnetization Tetragonal Ferrite-Based Films Induced by Carbon and Oxygen Vacancy Pairs

Herein, a low-temperature thermal decomposition method is utilized to grow new stable tetragonal Fe₃O₄-based thick ferrite films. The tetragonal Fe₃O₄-based film possesses high saturation magnetization of ∼800 emu/cm³. Doping with approximately 10% Co results in a high-energy product of ∼10.9 MGOe with perpendicular magnetocrystalline anisotropy, whereas doping with Ni increases electrical resistivity by a factor of 6 and retains excellent soft magnetic properties (high saturation magnetization and low coercivity). A combined experimental and first-principles study reveals that carbon interstitials (C_i^B) and oxygen vacancies (V_O) form C_i^B-V_O pairs which stabilize the tetragonal phase and enhance saturation magnetization. The magnetization enhancement is further attributed to local ferromagnetic coupling between Fe_A and Fe_B induced by C_i^B-V_O pairs in a tetragonal spinel ferrite lattice.

Out-of-plane magnetic anisotropy energy in the Ni3Bz3 molecule

Ni₃Bz₃ molecule shows a large magnetic anisotropy energy of 8 meV, with the easy axis perpendicular to the plane of Ni metal atoms. Note that the corresponding bare Ni₃ cluster has an in-plane easy axis.

Large magnetization modulation in ZnO-based memory devices with embedded graphene quantum dots

Magnetization modulation in oxide-based resistive random-access memories facilitates their application in multifunctional memory devices and spintronics. However, the small magnetization modulation in oxide films hinders their practical applications. In this paper, we report a significant enhancement in the magnetization modulation of ZnO films upon embedding graphene quantum dots (GQDs). The magnetization-modulation ratio is greater than 500% in the ZnO-GQD hybrid films under applied biases of only 0.23/-0.20 V. This magnetization-modulation ratio is the highest value reported to date in pure or magnetic-ion-doped metal-oxide films. Further analyses indicate that the exchange of oxygen between the GQDs and ZnO, under a reversible electric field, plays an important role in enhancing the magnetization modulation. This work provides a new direction for the application of GQDs.

Large Magnetoelectric Effects in Electrodeposited Nanoporous Microdisks Driven by Effective Surface Charging and Magneto-Ionics

A synergetic approach to enhance magnetoelectric effects (i.e., control of magnetism with voltage) and improve energy efficiency in magnetically actuated devices is presented. The investigated material consists of an ordered array of Co-Pt microdisks, in which nanoporosity and partial oxidation are introduced during the synthetic procedure to synergetically boost the effects of electric field. The microdisks are grown by electrodeposition from an electrolyte containing an amphiphilic polymeric surfactant. The bath formulation is designed to favor the incorporation of oxygen in the form of cobalt oxide. A pronounced reduction of coercivity (88%) and a remarkable increase of Kerr signal amplitude (60%) are observed at room temperature upon subjecting the microdisks to negative voltages through an electrical double layer. These large voltage-induced changes in the magnetic properties of the microdisks are due to (i) the high surface-area-to-volume ratio with ultranarrow pore walls (sub-10 nm) that promote enhanced electric charge accumulation and (ii) magneto-ionic effects, where voltage-driven O^2- migration promotes a partial reduction of CoO to Co at room temperature. This simple and versatile procedure to fabricate patterned "nano-in-micro" magnetic motifs with adjustable voltage-driven magnetic properties is very appealing for energy-efficient magnetic recording systems and other magnetoelectronic devices.

Atomic-scale imaging of the ferrimagnetic/diamagnetic interface in Au-Fe3O4 nanodimers and correlated exchange-bias origin

Exchange-biased magnetic heterostructures have become one of the research frontiers due to their significance in enriching the fundamental knowledge in nanomagnetics and promising diverse applications in the information industry. However, the physical origin of their exchange bias effect is still controversial. A key reason for this is the lack of unequivocal observations of interface growth. In this work, we fill this gap by experimentally imaging the ferrimagnetic/diamagnetic interfaces of Au-Fe₃O₄ nanodimers at the atomic level. A different physical mechanism from the reported mechanisms is found based on the atomic-resolution observation of their interfacial structure and electronic states, which reveals that the antiferromagnetic and ferromagnetic interactions of the formed weak/strong ferrimagnetic bilayer are responsible for the intrinsic exchange-bias origin in Au-Fe₃O₄ nanodimers. The theoretical quantitative analysis of the exchange bias shift based on the observed interfacial occupation model agrees well with the experimental value for the exchange bias effect, strongly verifying the proposed exchange-bias mechanism.

Structural and magnetic properties of bulk Mn2PtSn

Interplay between structural and magnetic order parameters is one of the key mechanisms of tuning properties of materials intended for device applications in spintronics. Here, using density functional calculations, we study combined effects of tetragonal distortion and non-collinear magnetic order in Mn₂PtSn. We show that this material has two energetically close energy minimums corresponding to tetragonal lattice. In one of these phases, Mn₂PtSn exhibits ferrimagnetic order with nearly fully compensated total magnetic moment, while in the other phase that corresponds to the lowest energy, a non-collinear magnetic arrangement emerges, with very large canting angle of the Mn local magnetic moments. The non-collinear alignment is explained through the interplay of exchange couplings between nearest and next nearest neighbor Mn atoms. Results are compared with those reported in recent literature, both experimental and theoretical.

Electrically induced and detected Néel vector reversal in a collinear antiferromagnet

Antiferromagnets are enriching spintronics research by many favorable properties that include insensitivity to magnetic fields, neuromorphic memory characteristics, and ultra-fast spin dynamics. Designing memory devices with electrical writing and reading is one of the central topics of antiferromagnetic spintronics. So far, such a combined functionality has been demonstrated via 90° reorientations of the Néel vector generated by the current-induced spin orbit torque and sensed by the linear-response anisotropic magnetoresistance. Here we show that in the same antiferromagnetic CuMnAs films as used in these earlier experiments we can also control 180° Néel vector reversals by switching the polarity of the writing current. Moreover, the two stable states with opposite Néel vector orientations in this collinear antiferromagnet can be electrically distinguished by measuring a second-order magnetoresistance effect. We discuss the general magnetic point group symmetries allowing for this electrical readout effect and its specific microscopic origin in CuMnAs.

Magnetization dynamics induced by the Rashba effect in ferromagnetic films

Manipulating the magnetization of ferromagnets by the current-induced spin-orbit torque has great potential application in the design of low energy consumption spintronic devices. Normally, an external magnetic field is needed for the reversal of current assisted magnetization by the spin-orbit torque. Recently, the switching of magnetization driven by the spin-orbit torque in the absence of an external magnetic field was reported in a Ta/Co₂₀Fe₆₀B₂₀/TaO_x system with lateral structural asymmetry. To understand the physics behind this experiment, we performed first principles calculations on the potential profile at the interface between the ferromagnetic film and the wedge-shaped deposited metal oxide in the Ta/Co/TaO system. This revealed that the lateral structural asymmetry generates two additional Rashba interactions which can reduce the minimum external field required to reverse the magnetization. In addition, we derived the Landau-Lifshitz-Gilbert equation from a quantum transport perspective and numerically investigated the magnetization dynamics in ferromagnetic films induced by Rashba interactions including those generated by lateral asymmetry. Our theoretical simulation provides microscopic explanations of experimental observations of magnetization switching in the absence of an external field of devices with lateral structural asymmetry.

Voltage-Controlled Magnetoresistance in Silicon Nanowire Transistors

Magneto-electronic logic is an innovative approach to performing high-efficiency computations. Additionally, the ultra-large scale integration requirement for computation strongly suggests exploiting magnetoresistance effects in non-magnetic semiconductor materials. Here, we demonstrate the magnetoresistance effect in a silicon nanowire field effect transistor (SNWT) fabricated by complementary metal-oxide-semiconductor (CMOS)-compatible technology. Our experimental results show that the sign and the magnitude of the magnetoresistance in SNWTs can be effectively controlled by the drain-source voltage and the gate-source voltage, respectively, playing the role of a multi-terminal tunable magnetoresistance device. Various current models are established and in good agreement with the experimental results that describe the impact of electrical voltage and magnetic field on magnetoresistance, which provides design feasibility for the high-density magneto-electronic circuit. Such findings will further pave the way for nanoscale silicon-based magneto-electronics logic devices and show a possible path beyond the developmental limits of CMOS logic.

Toward the Absolute Spin-Valve Effect in Superconducting Tunnel Junctions

A superconductor with a spin-split excitation spectrum behaves as an ideal ferromagnetic spin-injector in a tunneling junction. It was theoretically predicted that the combination of two such spin-split superconductors with independently tunable magnetizations may be used as an ideal absolute spin-valve. Here, we report on the first switchable superconducting spin-valve based on two EuS/Al bilayers coupled through an aluminum oxide tunnel barrier. The spin-valve shows a relative resistance change between the parallel and antiparallel configuration of the EuS layers up to 900% that demonstrates a highly spin-polarized current through the junction. Our device may be pivotal for realization of thermoelectric radiation detectors, a logical element for a memory cell in cryogenics, superconductor-based computers, and superconducting spintronics in general.

Spin polarization and spin channel reversal in graphitic carbon nitrides on top of an α-Fe2O3(0001) surface

Inducing the spin-dependent characteristics in two-dimensional (2D) materials by magnetic proximity effects is a recent targeted route for 2D spintronic devices. Here, we report the spin-dependent electronic properties of graphitic carbon nitrides (g-C2N, g-C3N and g-C4N3) on top of α-Fe2O3(0001) by first-principles calculations. The different terminations of α-Fe2O3(0001) can switch the conductivity of g-C2N from the n- to the p-type. In particular, the O- and single Fe-terminated interfaces show a half-metallic feature in g-C2N, which originates from the charge redistribution driven by work function difference and interfacial interaction. Additionally, the O-terminated interface shows stable physical adsorption, which leads to spin polarization in g-C3N and spin channel reversal in g-C4N3. These results strongly reveal that this novel system is a candidate for future graphitic carbon nitride-based spintronic devices.

Room-temperature high spin-orbit torque due to quantum confinement in sputtered BixSe(1-x) films

The spin-orbit torque (SOT) that arises from materials with large spin-orbit coupling promises a path for ultralow power and fast magnetic-based storage and computational devices. We investigated the SOT from magnetron-sputtered Bi_xSe_(1-x) thin films in Bi_xSe_(1-x)/Co₂₀Fe₆₀B₂₀ heterostructures by using d.c. planar Hall and spin-torque ferromagnetic resonance (ST-FMR) methods. Remarkably, the spin torque efficiency (θ_S) was determined to be as large as 18.62 ± 0.13 and 8.67 ± 1.08 using the d.c. planar Hall and ST-FMR methods, respectively. Moreover, switching of the perpendicular CoFeB multilayers using the SOT from the Bi_xSe_(1-x) was observed at room temperature with a low critical magnetization switching current density of 4.3 × 10⁵ A cm^-2. Quantum transport simulations using a realistic sp³ tight-binding model suggests that the high SOT in sputtered Bi_xSe_(1-x) is due to the quantum confinement effect with a charge-to-spin conversion efficiency that enhances with reduced size and dimensionality. The demonstrated θ_S, ease of growth of the films on a silicon substrate and successful growth and switching of perpendicular CoFeB multilayers on Bi_xSe_(1-x) films provide an avenue for the use of Bi_xSe_(1-x) as a spin density generator in SOT-based memory and logic devices.

Anisotropic Magneto-Coulomb Properties of 2D-0D Heterostructure Single Electron Device

Fabrication and spintronics properties of 2D-0D heterostructures are reported. Devices based on graphene ("Gr")-aluminium nanoclusters heterostructures show robust and reproducible single-electron transport features, in addition to spin-dependent functionality when using a top magnetic electrode. The magnetic orientation of this single ferromagnetic electrode enables the modulation of the environmental charge experienced by the aluminium nanoclusters. This anisotropic magneto-Coulomb effect, originating from spin-orbit coupling within the ferromagnetic electrode, provides tunable spin valve-like magnetoresistance signatures without the requirement of spin coherent charge tunneling. These results extend the capability of Gr to act both as electrode and as a platform for the growth of 2D-0D mixed-dimensional van der Waals heterostructures, providing magnetic functionalities in the Coulomb blockade regime on scalable spintronic devices. These heterostructures pave the way towards novel device architectures at the crossroads of 2D material physics and spin electronics.

Electromagnetic Functionalization of Wide-Bandgap Dielectric Oxides by Boron Interstitial Doping

A surge in interest of oxide-based materials is testimony for their potential utility in a wide array of device applications and offers a fascinating landscape for tuning the functional properties through a variety of physical and chemical parameters. In particular, selective electronic/defect doping has been demonstrated to be vital in tailoring novel functionalities, not existing in the bulk host oxides. Here, an extraordinary interstitial doping effect is demonstrated centered around a light element, boron (B). The host matrix is a novel composite system, made from discrete bulk LaAlO₃ :LaBO₃ compounds. The findings show a spontaneous ordering of the interstitial B cations within the host LaAlO₃ lattices, and subsequent spin-polarized charge injection into the neighboring cations. This leads to a series of remarkable cation-dominated electrical switching and high-temperature ferromagnetism. Hence, the induced interstitial doping serves to transform a nonmagnetic insulating bulk oxide into a ferromagnetic ionic-electronic conductor. This unique interstitial B doping effect upon its control is proposed to be as a general route for extracting/modifying multifunctional properties in bulk oxides utilized in energy and spin-based applications.