Magnetic Field Switching Research Articles

Smart composite hydrogel with magnetocaloric anisotropy for controllable multi-drug release

Controllable multi-drug release has been achieved by constructing a unique composite hydrogel structure comprising two layers of agar hydrogel, each incorporated with magnetically aligned anisotropic Fe3O4 nanorods. With the orthogonal alignment of the Fe3O4 nanorods chains in the two layers, controllable multi-drug release can be triggered by the magnetocaloric anisotropy in different layers of the composite hydrogel, depending on the direction of the external alternating magnetic field. The thermal-triggered release of methylene blue (MB) increases up to 1.4 folds by switching magnetic field direction from 0° to 90°. The physical origin of magnetocaloric anisotropy is magnetic anisotropy. The as-designed composite hydrogel displays an obvious opposite drug release trend by switching the magnetic field direction from 0° to 90°. This opposite drug release trend maintains significantly after more than 4 times of magnetic field direction switching. This work opens a promising avenue for realizing the combination of magnetic hyperthermia and remotely controllable multi-drug combination therapy.

Thermal activation on microwave-assisted magnetization switching in Co/Pt nanodot arrays

The magnetization switching field is efficiently reduced by exciting precession with a microwave field of GHz frequency. Analytical calculations based on the Landau–Lifshitz–Gilbert equation have revealed that the effect of the thermal activation process plays an important role in magnetization switching behavior under a microwave field. In this study, we experimentally investigated the microwave-assisted magnetization switching (MAS) behavior of Co/Pt nanodot arrays under various microwave field conditions. Experimental results were compared with the calculated effective energy barrier height of MAS. Consequently, all the experimental MAS behaviors can be explained by the effect of thermal activation, but quantitative discussion will require accurate experimental studies.

Magnetic field switching of Weyl semimetal associated with quantum criticality in one-dimensional extended Su-Schrieffer-Heeger chain

Graphene/silicon nanoribbons (G/SiNRs) provide low-dimensional platforms to engineer the topological characters for carbon/silicon-based electronics. Herein, we propose a one-dimensional (1D) extended Su-Schrieffer-Heeger (SSH) model to describe the G/SiNRs with a superlattice consisting of two interacting dimers, in which the topological quantum phase transition (QPT) and quantum criticality are investigated. The trivial band insulator transition into a nontrivial topological insulator via a critical Dirac semimetal is revealed, the self-duality of which is manifested by the zero value of Grüneisen ratio (GR) irrelevant of temperature. In a magnetic field, the time-reversal symmetry is broken such that the Weyl semimetal appears and is switched by a critical quadratic contact point semimetal with gap closing, at which the quantum criticality is not self-dual with GR Γ∼±T−1. Furthermore, the quantum critical scaling is done to analyze the quantum criticality, which provides a new clue to detect the QPT. The low-temperature specific heat demonstrates the low-lying excitation of gapped and gapless topological quantum phases explicitly.

Precise manipulation of the charge percolation networks of flow-electrode capacitive deionization using a pulsed magnetic field

Magnetic field is a simple and powerful means that enables controlled the transport of electrode particles in flow electrode capacitive deionization (FCDI). However, the magnetic particles are easily stripped from hybrid suspension electrodes and the precise manipulation of the charge percolation network remains challenging. In this study, a programmable magnetic field was introduced into the FCDI system to enhance the desalination performance and operational stability of magnetic FCDI, with core-shell magnetic carbon (MC) used as an alternative electrode additive. The results showed that the pulsed magnetic field (PMF) was more effective in enhancing the average salt removal rate (ASRR) compared to the constant magnetic field (CMF), with 51.6% and 67.7% enhancement, respectively, compared to the magnetic field-free condition. The outstanding advantage of the PMF lies in the enhancement in the trapping and mediating effects in the switching magnetic field, which keeps the concentration of the electrode particles near the current collector at a high level and greatly facilitates electron transport. In long-term operation (20,000 cycles), the pulsed magnetic FCDI achieved a stable desalinating rate of 0.4–0.68 μmol min–1 cm–2 and a charge efficiency of >96%. In brief, our study introduces a new approach for the precise manipulation of charge percolation networks of the suspension electrodes and provides insight into the charging mechanism of the magnetic FCDI.

Enhancement of Damping-Like Field and Field-Free Switching in Pt/(Co/Pt)/PtMn Trilayer Films Prepared in the Presence of an In Situ Magnetic Field.

The current-induced magnetization switching and damping-like field in Pt/(Co/Pt)/PtMn trilayer films prepared with and without an in situ in-plane field of 600 Oe have been studied systematically. In the presence of the in situ field, a small in-plane bias field (HEB) is observed for films with PtMn thickness ≥5 nm, while there is no observable HEB for PtMn thickness ≤3 nm. Nevertheless, a field-free switching of perpendicular magnetization of Co/Pt is observed for all the films with the PtMn thickness of 1-7 nm. On the other hand, without the presence of the in situ field, HEB and field-free switching are not seen. Furthermore, the damping-like fields (HDL) are much enhanced in the presence of the in situ field, and the increasement can be up to 47%. We further revealed that the spin current is mainly from the Pt layer, while the noncollinear spin configuration at the interface caused by the in situ in-plane field may play a role in the HDL enhancement. Micromagnetic simulations indicate that the canting of antiferromagnet PtMn spins plays an important role in the field-free switching. Our findings clarify the source of spin current in the trilayer films and provide an easier approach to field-free switching and HDL enhancement for future low-power spintronic devices.

Structural relaxation in metastable magnetic submicronic wires

Changes triggered by low temperature metastable relaxation annealing in the peculiar magnetic behavior of rapidly solidified submicronic amorphous wires are reported. The overall aim was to understand the effects of the associated stress relief process on magnetization switching and magnetic domain wall propagation in these low dimensional amorphous wires with cylindrical symmetry. The results have shown that, even though the employed relatively low annealing temperatures did not initiate any crystallization, i.e., the amorphous state has been preserved, the consequences in terms of magnetic behavior are significant, with important variations in both magnetic switching field and domain wall velocity values. The observed modifications have been interpreted based on the interplay between the magnetoelastic and magnetostatic anisotropies within the submicronic amorphous wires, as well as on the complex changes in the underlying nonlinear stress distribution generated by the rapid solidification process. The outcomes of this investigation, alongside the general framework for their explanation, have unraveled novel ways of accurately tailoring and controlling the magnetic characteristics of the amorphous submicronic wires for developing new applications in sensors and domain wall logic devices, in which rapid switching and fast domain walls can make an important impact.

Enhanced Magnetorheological Behavior of a Carbonyl‐Iron‐Based Fluid via Addition of Fe3O4/Halloysite‐Nanotube Composite Particles

Composite additives for enhancing the yield stress, sedimentation stability, and long‐term reversibility of bidisperse magnetorheological fluids (MRFs) are reported herein. The design and introduction of magnetic Fe3O4/halloysite‐nanotube (HNT) composite additives to carbonyl‐iron (CI)‐based MRFs are described, and the effects of Fe3O4/HNT addition on the MRF behavior are elucidated. The rheological, viscoelastic, and cyclic reversibility analyses of the bidisperse Fe3O4/HNT‐CI MRFs indicate that the MR performance increases and subsequently decreases with the increasing content of the Fe3O4/HNTs. The MRF containing 1.0 wt% Fe3O4/HNTs shows optimal MR properties and long‐term reversibility. Under a magnetic field, the 1.0 wt% Fe3O4/HNTs are embedded in the interstices of the magnetic chains, enhancing the magnetic dipole–dipole interactions between the particles, strengthening the rigidity of the magnetic chains, and increasing the yield stress of the MRF. The Fe3O4/HNTs are adsorbed on the surfaces of the CI particles in the absence of a magnetic field, occupying the free space between the CI particles and forming support structures, which prevents aggregation and improves sedimentation stability. Moreover, the designed MRFs respond quickly to magnetic field switching and exhibit enhanced long‐term reversibility.

Stochastic Magnetization Switching in Rapidly Solidified (Co0.94Fe0.06)72.5Si12.5B15 Amorphous Submicronic Wires.

Submicrometric magnetic amorphous wires are good candidates for future development of miniaturized sensors and magnetic logic applications. Here we report the results of an in-depth investigation of magnetization switching in rapidly solidified nearly zero magnetostrictive (Co0.94Fe0.06)72.5Si12.5B15 amorphous samples with diameters of the actual magnetic wires between 300 and 450 nm. All samples were found to be magnetically bistable, displaying characteristic rectangular hysteresis loops. This shows that magnetization reversal occurs through the depinning and subsequent propagation of a magnetic domain wall, whose velocity depends on the applied field and on the sample dimensions. The results of this study reveal stochastic nonlinear dependencies of both the magnetic switching field and the domain wall velocity on the sample diameter. The analysis of the potential causes, which include nonlinear residual stresses, fluctuations in wire dimensions (metal and glass), and competing magnetic anisotropies of different origins, show that a combination of all three factors could lead to the observed stochastic behavior. Calculated values of the switching field, which consider only changes in the wire dimensions, indicate that such influence alone cannot account for the strong nonlinearities. The results are important for the applications of such ultrathin cylindrical magnetic amorphous wires.

Magnetic anisotropy and reversal in epitaxial FeGa/IrMn bilayers with different orientations of exchange bias

Epitaxial FeGa/IrMn bilayers with exchange biases along the FeGa[100] and [110] directions are prepared on MgO(001) single crystal substrates by magnetron sputtering through controlling the orientation of the external field <i>in situ</i> applied during growth. The effect of the exchange bias orientation on the magnetic switching process and the magnetic switching field are studied. The X-ray <i>φ</i>-scan indicates that the FeGa layer is epitaxially grown with a 45° in-plane rotation on the MgO(001) substrate along the FeGa(001)[110] direction and the MgO(001)[100] direction. The measurements of the angular dependence of the ferromagnetic resonance field and the corresponding fitting to the Kittel equation show that the samples have a superposition of fourfold symmetric magnetocrystalline anisotropy <inline-formula><tex-math id="M4">\begin{document}$ {K}_{1} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M4.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M4.png"/></alternatives></inline-formula>, unidirectional magnetic exchange bias anisotropy <inline-formula><tex-math id="M5">\begin{document}$ {K}_{\mathrm{e}\mathrm{b}} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M5.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M5.png"/></alternatives></inline-formula>, and uniaxial magnetic anisotropy <inline-formula><tex-math id="M6">\begin{document}$ {K}_{\mathrm{u}} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M6.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M6.png"/></alternatives></inline-formula> with configuration of <inline-formula><tex-math id="M7">\begin{document}$ {K}_{\mathrm{e}\mathrm{b}}//\left[100\right] $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M7.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M7.png"/></alternatives></inline-formula> or <inline-formula><tex-math id="M8">\begin{document}$ {K}_{\mathrm{e}\mathrm{b}}//\left[110\right] $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M8.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M8.png"/></alternatives></inline-formula>. The combined longitudinal and transverse magneto-optical Kerr effect measurements show that sample with <inline-formula><tex-math id="M9">\begin{document}$ {K}_{\mathrm{e}\mathrm{b}}//\left[100\right] $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M9.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M9.png"/></alternatives></inline-formula> exhibits square loops, asymmetrically shaped loops, and one-sided two-step loops in different external magnetic field directions. In contrast, the sample with <inline-formula><tex-math id="M10">\begin{document}$ {K}_{\mathrm{e}\mathrm{b}}//\left[110\right] $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M10.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M10.png"/></alternatives></inline-formula> exhibits one-sided two-step and two-sided two-step loops as the magnetic field orientation changes. Because the <inline-formula><tex-math id="M11">\begin{document}$ {K}_{1} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M11.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M11.png"/></alternatives></inline-formula> is superimposed by <inline-formula><tex-math id="M12">\begin{document}$ {K}_{\mathrm{u}} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M12.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M12.png"/></alternatives></inline-formula> and <inline-formula><tex-math id="M13">\begin{document}$ {K}_{\mathrm{e}\mathrm{b}} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M13.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M13.png"/></alternatives></inline-formula>, the in-plane fourfold symmetry of the magnetic anisotropy energy is broken. The local minima are no longer strictly along the in-plane <inline-formula><tex-math id="M14">\begin{document}$ \left\langle{100}\right\rangle $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M14.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M14.png"/></alternatives></inline-formula> directions, but make a deviation angle which depends on the relative orientation and strength of magnetic anisotropy. A model based on the domain wall nucleation and propagation is proposed with considering the different orientations of <inline-formula><tex-math id="M15">\begin{document}$ {K}_{\mathrm{e}\mathrm{b}} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M15.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M15.png"/></alternatives></inline-formula>, which can nicely explain the change of the magnetic switching route with the magnetic field orientation and fit the angular dependence of the magnetic switching fields, indicating a significant change of domain wall nucleation energy as the orientation of <inline-formula><tex-math id="M16">\begin{document}$ {K}_{\mathrm{e}\mathrm{b}} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M16.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M16.png"/></alternatives></inline-formula> changes.

Simulation of Shape and Structure Response of Nonspherical Magnetosensitive Vesicles Subjected to Magnetic Fields

Molecular dynamics simulation is performed to study coupled magnetic, structural, and mechanical response of magnetosensitive vesicles to quasistatic on/off switching of external magnetic field. The vesicle membrane filled with magnetic nanoparticles is modeled in the coarse-grained bead-spring representation. In detail it is shown, how discocyte- and stomatocyte-like vesicles respond to uniform magnetic field. Notably, having undergone an on/off switching cycle, a vesicle does not always restore in full its shape.

Thermoresponsive, magnetic, adhesive and conductive nanocomposite hydrogels for wireless and non-contact flexible sensors

Hydrogel sensors are increasingly investigated and applied in emerging flexible electronics, but the exploration of hydrogel sensors with multiple functionalities remains a challenge. In this work, thermoresponsive, magnetic, adhesive and conductive nanocomposite hydrogels are developed and further applied in fabricating multi-functional flexible sensors. In such nanocomposite hydrogels, poly(N-isopropyl acrylamide-co-acrylamide) (P(NIPAAm-co-Am)) and Fe3O4 nanoparticles are designed as the thermoresponsive and magnetic component respectively, poly(vinyl alcohol) (PVA) is introduced in a semi-interpenetrating way to enhance the adhesiveness and mechanical property, and potassium chloride (KCl) works as the conductive component. Interestingly, the adhesion property is switchable by temperature based on the thermoresponsiveness of the nanocomposite hydrogels. Resistive strain sensors assembled from the nanocomposite hydrogels achieve a gauge factor (GF) of 4.21, a response time of 140 ms, stability of 2000 sensing cycles and excellent reversibility. Such nanocomposite hydrogel sensors are used as wearable sensors for monitoring diverse human motions and further integrated with Bluetooth signal transmission and reception system to fabricate wireless wearable sensors. Because of the deformation of nanocomposite hydrogels in switching magnetic field, the nanocomposite hydrogel sensors also have the ability to respond in a non-contact way to switching magnetic fields.

Thermal and Magnetic Field Switching in a Two‐Step Hysteretic MnIII Spin Crossover Compound Coupled to Symmetry Breakings

AbstractA MnIII spin crossover complex with atypical two‐step hysteretic thermal switching at 74 K and 84 K shows rich structural–magnetic interplay and magnetic‐field‐induced spin state switching below 14 T with an onset below 5 T. The spin states, structures, and the nature of the phase transitions are elucidated via X‐ray and magnetization measurements. An unusual intermediate phase containing four individual sites, where are in a pure low spin state, is observed. The splitting of equivalent sites in the high temperature phase into four inequivalent sites is due to a structural reorganization involving a primary and a secondary symmetry‐breaking order parameter that induces a crystal system change from orthorhombic→monoclinic and a cell doubling. Further cooling leads to a reconstructive phase transition and a monoclinic low‐temperature phase with two inequivalent low‐spin sites. The coupling between the order parameters is identified in the framework of Landau theory.

Thermal and Magnetic Field Switching in a Two-Step Hysteretic MnIII Spin Crossover Compound Coupled to Symmetry Breakings.

A MnIII spin crossover complex with atypical two-step hysteretic thermal switching at 74 K and 84 K shows rich structural-magnetic interplay and magnetic-field-induced spin state switching below 14 T with an onset below 5 T. The spin states, structures, and the nature of the phase transitions are elucidated via X-ray and magnetization measurements. An unusual intermediate phase containing four individual sites, where are in a pure low spin state, is observed. The splitting of equivalent sites in the high temperature phase into four inequivalent sites is due to a structural reorganization involving a primary and a secondary symmetry-breaking order parameter that induces a crystal system change from orthorhombic→monoclinic and a cell doubling. Further cooling leads to a reconstructive phase transition and a monoclinic low-temperature phase with two inequivalent low-spin sites. The coupling between the order parameters is identified in the framework of Landau theory.

Magnetic memory driven by topological insulators

Giant spin-orbit torque (SOT) from topological insulators (TIs) provides an energy efficient writing method for magnetic memory, which, however, is still premature for practical applications due to the challenge of the integration with magnetic tunnel junctions (MTJs). Here, we demonstrate a functional TI-MTJ device that could become the core element of the future energy-efficient spintronic devices, such as SOT-based magnetic random-access memory (SOT-MRAM). The state-of-the-art tunneling magnetoresistance (TMR) ratio of 102% and the ultralow switching current density of 1.2 × 105 A cm−2 have been simultaneously achieved in the TI-MTJ device at room temperature, laying down the foundation for TI-driven SOT-MRAM. The charge-spin conversion efficiency θSH in TIs is quantified by both the SOT-induced shift of the magnetic switching field (θSH = 1.59) and the SOT-induced ferromagnetic resonance (ST-FMR) (θSH = 1.02), which is one order of magnitude larger than that in conventional heavy metals. These results inspire a revolution of SOT-MRAM from classical to quantum materials, with great potential to further reduce the energy consumption.

A Spin-Valve GMR Based Sensor with Magnetite@silver Core-Shell Nanoparticles as a Tag for Bovine Serum Albumin Detection

The availability of rapid-portable instruments to monitor the bovine serum albumin (BSA) concentration is vital in the early detection of disease. In this research, an original biosensing method based on a spin-valve giant magnetoresistance as a transducer and magnetite@silver core–shell magnetic nanoparticles (MNPs) as a tag has been proposed for detecting BSA. The synthesized magnetite@silver MNPs tag size is ≈15 nm with ≈52 emu g−1 of saturation magnetization. This proposed biosensor performs rapid detection of BSA through the shifting of the switching magnetic field and the increasing of the output voltage. The effectivity of the sensor in monitoring the BSA concentration was shown by a strong linear correlation with ≈0.06 mV/(mg/ml) of the sensitivity and ≈0.44 mg ml−1 of the detection limit. Moreover, the measurement result can be acquired rapidly up to 1 min with low external magnetic field assistance. Therefore, this biosensing technique can be promoted as a real-time portable biosensor.

Ion beam etching dependence of spin–orbit torque memory devices with switching current densities reduced by Hf interlayers

We report on the fabrication of nanoscale, three-terminal in-plane spin–orbit torque switching devices with low switching current densities. Critical parameters in the fabrication process, including the ion beam etching angle and time, were optimized to avoid fabrication defects and improve device yield. Measurements of the magnetic field and current-induced switching behavior of the tunnel junctions demonstrate a sensitivity to the nanopillar aspect ratio, which dictates the nanopillars’ anisotropy and thermal stability. Additionally, we show that the current density required for switching can be reduced and the device thermal stability increased by inserting Hf interlayers into the heterostructure. Micromagnetic simulations are generally consistent with the experimentally observed switching behavior, suggesting an increase in the interfacial perpendicular anisotropy at the CoFeB/MgO interface and the reduction in the Dzyaloshinskii–Moriya interaction at the W/CoFeB interface by the Hf interlayers.

Stimulated Nucleation of Skyrmions in a Centrosymmetric Magnet.

Understanding the dynamics of skyrmion nucleation and manipulation is important for applications in spintronic devices. In this contribution, the spin textures at magnetic domain-boundaries stimulated by application of in-plane magnetic fields in a centrosymmetric kagome ferromagnet, Fe3Sn2, with thickness gradient are investigated using Lorentz transmission electron microscopy. Switching of the in-plane magnetic field is shown to induce a reversible transformation from magnetic stripes to skyrmions, or vice versa, at the interface between differently oriented domains. Micromagnetic simulations combined with experiments reveal that the rotatable anisotropy and thickness dependence of the response to the external in-plane field are the critical factors for the skyrmion formation. In addition, it is shown that the helicity of skyrmions can also be controlled using this dynamic process. The results suggest that magnetic materials with rotatable anisotropy are potential skyrmionic systems and provides a different approach for nucleation and manipulation of skyrmions in spintronic devices.

Tunable spin-flop transition in artificial ferrimagnets

Spin-flop transition (SFT) consists in a jump-like reversal of antiferromagnetic (AF) lattice into a noncollinear state when the magnetic field increases above the critical value. Potentially the SFT can be utilized in many applications of a rapidly developing AF spintronics. However, the difficulty of using them in conventional antiferromagnets lies in (a) too large switching magnetic fields (b) the need for presence of a magnetic anisotropy, and (c) requirement to apply magnetic field along the correspondent anisotropy axis. In this work we propose to use artificial ferrimagnets (FEMs) in which the SFT occurs without anisotropy and the transition field can be lowered by adjusting exchange coupling in the structure. This is proved by experiment on artificial Fe-Gd FEMs where usage of Pd spacers allowed us to suppress the transition field by two orders of magnitude.

Voltage-Gate-Assisted Spin-Orbit-Torque Magnetic Random-Access Memory for High-Density and Low-Power Embedded Applications

Voltage-gate assisted spin-orbit torque (VGSOT) writing scheme combines the advantages from voltage control of magnetic anisotropy (VCMA) and spin-orbit torque (SOT) effects, enabling multiple benefits for magnetic random access memory (MRAM) applications. In this work, we give a complete description of VGSOT writing properties on perpendicular magnetic tunnel junction (pMTJ) devices, and we propose a detailed methodology for its electrical characterization. The impact of gate assistance on the SOT switching characteristics are investigated using electrical pulses down to 400ps. The VCMA coefficient ({\xi}) extracted from current switching scheme is found to be the same as that from the magnetic field switch method, which is in the order of 15fJ/Vm for the 80nm to 150nm devices. Moreover, as expected from the pure electronic VCMA effect, {\xi} is revealed to be independent of the writing speed and gate length. We observe that SOT switching current characteristics are modified linearly with gate voltage (V_g), similar as for the magnetic properties. We interpret this linear behavior as the direct modification of perpendicular magnetic anisotropy (PMA) and nucleation energy induced by VCMA. At V_g = 1V, the SOT write current is decreased by 25%, corresponding to a 45% reduction in total energy down to 30fJ/bit at 400ps speed for the 80nm devices used in this study. Further, the device-scaling criteria are proposed, and we reveal that VGSOT scheme is of great interest as it can mitigate the complex material requirements of achieving high SOT and VCMA parameters for scaled MTJs. Finally, how that VGSOT-MRAM can enable high-density arrays close to two terminal geometries, with high-speed performance and low-power operation, showing great potential for embedded memories as well as in-memory computing applications at advanced technology nodes.

Spin splitting effect in semiconductor-based magnetoresistance device

Semiconductor-based magnetoresistance (MR) device has many advantages such as high MR ratio at low switching magnetic field, but electron spins were ignored completely in previous researches. Electron spins should impact on performance of semiconductor-based MR device, as electron spins interact with magnetic fields. By considering a semiconductor microstructure constructed on GaAs/Al x Ga 1-x As heterostructure by patterning two asymmetric ferromagnetic (FM) stripes, we theoretically explore effect of electron spins on semiconductor-based MR device. An interesting spin splitting effect is found in semiconductor-based MR device. Both magnitude and sign of spin splitting effect can be modified by applying a negative voltage. These findings may be helpful for designing semiconductor-based MR devices. • Spin effect on semiconductor-based MR device is studied theoretically. • An interesting spin splitting phenomenon is found. • Spin splitting can be tuned by applying a negative voltage. • A controllable semiconductor-based MR device may be obtained.