We have investigated Surface Acoustic Wave (SAW) induced ferromagnetic resonance (FMR) assisted Spin Transfer Torque (STT) switching of perpendicular MTJ (p-MTJ) with inhomogeneities using micromagnetic simulations that include the effect of thermal noise. With suitable frequency excitation, the SAW can induce ferromagnetic resonance in magnetostrictive materials, and the magnetization can precesses in a cone with high deflection from the perpendicular direction. With incorporation of inhomogeneity via lateral anisotropy variation as well as room temperature thermal noise, the magnetization precession in different gains can be significantly incoherent. Interestingly, the precession in different grains are found to be in phase, even though the precession amplitude (angle of deflection from the perpendicular direction) vary across grains of different anisotropy. Nevertheless, the high mean deflection angle can complement the STT switching by reducing the STT current significantly; even though the applied stress induced change in anisotropy is much lower than the total anisotropy barrier. This work indicates that SAW assisted switching can improve energy efficiency while being scalable to very small dimensions, which is technologically important for STT-RAM and elucidates the physical mechanism for the potential robustness of this paradigm in realistic scenarios with thermal noise and material inhomogeneity
Spin-transfer ferromagnetic resonance (ST-FMR) in symmetric magnetic tunnel junctions (MTJs) with a varied thickness of the MgO tunnel barrier (0.75 nm < $t_{MgO}$ < 1.05 nm) is studied using the spin-torque diode effect. The application of an RF current into nanosized MTJs generates a DC mixing voltage across the device when the frequency is in resonance with the resistance oscillations arising from the spin transfer torque. Magnetization precession in the free and reference layers of the MTJs is analyzed by comparing ST-FMR signals with macrospin and micromagnetic simulations. From ST-FMR sp…
Thermal-magnetic noise at ferromagnetic resonance (T-FMR) can be used to measure magnetic perpendicular anisotropy of nanoscale magnetic tunnel junctions (MTJs). For this purpose, T-FMR measurements were conducted with an external magnetic field up to 14 kOe applied perpendicular to the film surface of MgO-based MTJs under a dc bias. The observed frequency-field relationship suggests that a 20 A CoFeB free layer has an effective demagnetization field much smaller than the intrinsic bulk value of CoFeB, with 4PiMeff = (6.1 +/- 0.3) kOe. This value is consistent with the saturation field obtaine…
We demonstrate a technique of broadband spin torque ferromagnetic resonance (ST-FMR) with magnetic field modulation for measurements of spin wave properties in magnetic nanostructures. This technique gives great improvement in sensitivity over the conventional ST-FMR measurements, and application of this technique to nanoscale magnetic tunnel junctions (MTJs) reveals a rich spectrum of standing spin wave eigenmodes. Comparison of the ST-FMR measurements with micromagnetic simulations of the spin wave spectrum allows us to explain the character of low-frequency magnetic excitations in nanoscale…
Several experimental techniques have been introduced in recent years in attempts to measure spin transfer torque in magnetic tunnel junctions (MTJs). The dependence of spin torque on bias is important for understanding fundamental spin physics in magnetic devices and for applications. However, previous techniques have provided only indirect measures of the torque and their results to date for the bias dependence are qualitatively and quantitatively inconsistent. Here we demonstrate that spin torque in MTJs can be measured directly by using time-domain techniques to detect resonant magnetic pre…
We investigate fast-pulse switching of in-plane-magnetized magnetic tunnel junctions (MTJs) within 3-terminal devices in which spin-transfer torque is applied to the MTJ by the giant spin Hall effect. We measure reliable switching, with write error rates down to $10^{-5}$, using current pulses as short as just 2 ns in duration. This represents the fastest reliable switching reported to date for any spin-torque-driven magnetic memory geometry, and corresponds to a characteristic time scale that is significantly shorter than predicted possible within a macrospin model for in-plane MTJs subject t…
The tunnel magnetoresistance (TMR) in the magnetic tunnel junction (MTJ) with embedded nanoparticles (NPs) was calculated in range of the quantum-ballistic model. The simulation was performed for electron tunneling through the insulating layer with embedded magnetic and nonmagnetic NPs within the approach of the double barrier subsystem connected in parallel to the single barrier one. This model can be applied for both MTJs with in-plane magnetization and perpendicular one. We also calculated the in-plane component of the spin transfer torque (STT) versus the applied voltage in MTJs with magne…
We demonstrate excitation of ferromagnetic resonance in CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs) by the combined action of voltage-controlled magnetic anisotropy (VCMA) and spin transfer torque (ST). Our measurements reveal that GHz-frequency VCMA torque and ST in low-resistance MTJs have similar magnitudes, and thus that both torques are equally important for understanding high-frequency voltage-driven magnetization dynamics in MTJs. As an example, we show that VCMA can increase the sensitivity of an MTJ-based microwave signal detector to the sensitivity level of semiconductor Schottk…
The discovery of spin torque transfer (STT) has lead to a significant advance in the development of spintronic devices. Novel structures and materials have been studied in order to improve the performance of the magnetic tunnel junctions (MTJs) performances and understand the fundamental physics in spin torque transfer. The adiabatic spin torque effect, which is due to the spatial non-uniformity of magnetic properties, has been predicted in theory and demonstrated experimentally in magnetic nanowires. However, this important spin torque has been rarely concerned in the magnetic tunnel junction…
Using a first-principles noncollinear wave-function-matching method, we studied the spin-transfer torques (STTs) in CoFe/Mg-B-O/CoFe(001) magnetic tunnel junctions (MTJs), where three different types of B-doped MgO in the spacer are considered, including B atoms replacing Mg atoms (Mg$_3$BO$_4$), B atoms replacing O atoms (Mg$_4$BO$_3$), and B atoms occupying interstitial positions (Mg$_4$BO$_4$) in MgO. A strong asymmetric angular dependence of STT can be obtained both in ballistic CoFe/Mg$_3$BO$_4$ and CoFe/Mg$_4$BO$_4$ based MTJs, whereas a nearly symmetric STT curve is observed in the junc…
Spin-torque driven ferromagnetic resonance (ST-FMR) is used to study magnetic excitations in Co/Ni synthetic layers confined in nanojunctions. Field swept ST-FMR measurements were conducted with a magnetic field applied perpendicular to the layer surface. The resonance lines were measured under low amplitude excitation in a linear response regime. The resulting resonance fields were compared with those obtained using conventional rf field driven FMR on extended films with the same Co/Ni layer structure. A lower resonance field is found in confined structures. The effect of both dipolar fields …
We examine the spin torque (ST) response of magnetic tunnel junctions (MTJs) with ultra-thin MgO tunnel barrier layers to investigate the relationship between the spin-transfer torque and the tunnel magnetoresistance (TMR) under finite bias. We find that the spin torque per unit current exerted on the free layer decreases by less than 10% over a bias range where the TMR decreases by over 40%. We examine the implications of this result for various spin-polarized tunneling models and find that it is consistent with magnetic-state-dependent effective tunnel decay lengths.
With the rise in in-memory computing architectures to reduce the compute-memory bottleneck, a new bottleneck is present between analog and digital conversion. Analog content-addressable memories (ACAM) are being recently studied for in-memory computing to efficiently convert between analog and digital signals. Magnetic memory elements such as magnetic tunnel junctions (MTJs) could be useful for ACAM due to their low read/write energy and high endurance, but MTJs are usually restricted to digital values. The spin orbit torque-driven domain wall-magnetic tunnel junction (DW-MTJ) has been recentl…
Spin-torque driven ferromagnetic resonance (ST-FMR) is used to study thin Co/Ni synthetic layers with perpendicular anisotropy confined in spin-valve based nanojunctions. Field swept ST-FMR measurements were conducted with a magnetic field applied perpendicular to the layer surface. The resonance lines were measured under low amplitude rf excitation, from 1 to 20 GHz. These results are compared with those obtained using conventional rf field driven FMR on extended films with the same Co/Ni layer structure. The layers confined in spin valves have a lower resonance field, a narrower resonance li…
The spin-torque ferromagnetic resonance (ST-FMR) in a bilayer system consisting of a magnetic insulator such as Y3Fe5O12 and a normal metal with spin-orbit interaction such as Pt is addressed theoretically. We model the ST-FMR for all magnetization directions and in the presence of field-like spin-orbit torques based on the drift-diffusion spin model and quantum mechanical boundary conditions. ST-FMR experiments may expose crucial information about the spin-orbit coupling between currents and magnetization in the bilayers.
We have fabricated nanoscale magnetic tunnel junctions (MTJs) with an additional fixed magnetic layer added above the magnetic free layer of a standard MTJ structure. This acts as a second source of spin-polarized electrons that, depending on the relative alignment of the two fixed layers, either augments or diminishes the net spin-torque exerted on the free layer. The compound structure allows a quantitative comparison of spin-torque from tunneling electrons and from electrons passing through metallic spacer layers, as well as analysis of Joule selfheating effects. This has significance for c…
We study the combined effects of spin transfer torque, voltage modulation of interlayer exchange coupling and magnetic anisotropy on the switching behavior of perpendicular magnetic tunnel junctions (p-MTJs). In asymmetric p-MTJs, a linear-in-voltage dependence of interlayer exchange coupling enables the effective perpendicular anisotropy barrier to be lowered for both voltage polarities. This mechanism is shown to reduce the critical switching current and effective activation energy. Finally, we analyze the possibility of having switching via interlayer exchange coupling only.
The electrical detection of spin torque ferromagnetic resonance (st-FMR) is becoming a popular method for measuring the spin-Hall angle of heavy metals (HM). However, various sensible analysis on the same material with either the same or different experimental setups yielded different spin-Hall angles with large discrepancy, indicating some missing ingredients in our current understanding of st-FMR. Here we carry out a careful analysis of electrical signals of the st-FMR in a HM/ferromagnet (HM/FM) bilayer with an arbitrary magnetic anisotropy. The FM magnetization is driven by two radio-frequ…
Current-induced spin-transfer torques (STT) and spin-orbit torques (SOT) enable the electrical switching of magnetic tunnel junctions (MTJs) in nonvolatile magnetic random access memories. In order to develop faster memory devices, an improvement of the timescales underlying the current driven magnetization dynamics is required. Here we report all-electrical time-resolved measurements of magnetization reversal driven by SOT in a three-terminal MTJ device. Single-shot measurements of the MTJ resistance during current injection reveal that SOT switching involves a stochastic two-step process con…
Efficient generation of spin currents from charge currents is of high importance for memory and logic applications of spintronics. In particular, generation of spin currents from charge currents in high spin-orbit coupling metals has the potential to provide a scalable solution for embedded memory. We demonstrate a net reduction in critical charge current for spin torque driven magnetization reversal via using spin-orbit mediated spin current generation. We scaled the dimensions of the spin-orbit electrode to 400 nm and the nanomagnet to 270 nm x 68 nm in a three terminal spin-orbit torque, ma…
We study spin-orbit-torque-driven ferromagnetic resonance (FMR) in ferromagnetic (FM) bilayers, consisting of Co and permalloy (Py), sandwiched between Pt and MgO layers. We find that the FM layer in contact with the Pt layers dominantly determines that spin Hall angle, which is consistent with the spin-transparency model. By contrast, the FMR linewidths are considerably influenced not only by the spin-pumping effect across the Pt|FM in terface but also by the spin relaxation such as two-magnon scattering at the FMMgO interface.The CoMgO interface leads to notably increased FMR linewidths, whi…
We report the possibility of achieving an order of magnitude reduction in the energy dissipation needed to write bits in perpendicular magnetic tunnel junctions (p-MTJs) by simulating the magnetization dynamics under a combination of resonant surface acoustic waves (r-SAW) and spin-transfer-torque (STT). The magnetization dynamics were simulated using the Landau-Lifshitz-Gilbert equation under macrospin assumption with the inclusion of thermal noise. The resonant magnetization dynamics in the magnetostrictive nanomagnet build over few 10s of cycles of SAW application that drives the magnetizat…
Spin-valve based nanojunctions incorporating Co|Ni multilayers with perpendicular anisotropy were used to study spin-torque driven ferromagnetic resonance (ST-FMR) in a nonlinear regime. Perpendicular field swept resonance lines were measured under a large amplitude microwave current excitation, which produces a large angle precession of the Co|Ni layer magnetization. With increasing rf power the resonance lines broaden and become asymmetric, with their peak shifting to lower applied field. A nonhysteretic step jump in ST-FMR voltage signal was also observed at high powers. The results are ana…
This work investigates nanosecond superparamagnetic switching in 50 nm diameter in-plane magnetized magnetic tunnel junctions (MTJs). Due to the small in-plane uniaxial anisotropy, dwell times below 10 ns and auto-correlation times down to 5 ns are measured for circular superparamagnetic tunnel junctions (SMTJs). SMTJs exhibit probabilistic switching of the magnetic free layer, which can be used for the generation of true random numbers. The quality of random bitstreams, generated by our SMTJ, is evaluated with a statistical test suite (NIST STS, sp 800-22) and shows true randomness after thre…
We formulate a theory of the AC spin Hall magnetoresistance (SMR) in a bilayer system consisting of a magnetic insulator such as yttrium iron garnet (YIG) and a heavy metal such as platinum (Pt). We derive expressions for the DC voltage generation based on the drift-diffusion spin model and quantum mechanical boundary condition at the interface that reveal a spin torque ferromagnetic resonance (ST-FMR). We predict that ST-FMR experiments will reveal valuable information on the current-induced magnetization dynamics of magnetic insulators and AC spin Hall effect.
We use three-terminal magnetic tunnel junctions (MTJs) designed for field-free switching by spin-orbit torques (SOTs) to systematically study the impact of dual voltage pulses on the switching performances. We show that the concurrent action of an SOT pulse and an MTJ bias pulse allows for reducing the critical switching energy below the level typical of spin transfer torque while preserving the ability to switch the MTJ on the sub-ns time scale. By performing dc and real-time electrical measurements, we discriminate and quantify three effects arising from the MTJ bias: the voltage-controlled …
Spin-torque ferromagnetic resonance (ST-FMR) is a common method used to measure spin-orbit torques (SOTs) in heavy metal/ferromagnet bilayer structures. In the course of a measurement, other resonant processes such as spin pumping (SP) and heating can cause spin current or heat flows between the layers, inducing additional resonant voltage signals via the inverse spin Hall effect (ISHE) and Nernst effects (NE). In the standard ST-FMR geometry, these extra artifacts exhibit a dependence on the angle of an in-plane magnetic field that is identical to the rectification signal from the SOTs. We sh…
Spin orbit torques are of great interest for switching the magnetization direction in nanostructures, moving skyrmions and exciting spin waves. The standard method of determining their efficiency is by spin torque ferromagnetic resonance (ST-FMR), a technique that involves analyzing the resonance linewidth or lineshape. On microstuctures these two analysis methods are quite consistent. Here we present ST-FMR results on permalloy (Ni$_{80}$Fe$_{20}$) nanowires -- with widths varying from $150$ to 800 nm -- that show that the standard model used to analyze the resonance linewidth and lineshape g…
We use micromagnetic simulation to demonstrate layer-selective detection of magnetization directions from magnetic dots having two recording layers by using a spin-torque oscillator (STO) as a read device. This method is based on ferromagnetic resonance (FMR) excitation of recording-layer magnetizations by the microwave field from the STO. The FMR excitation affects the oscillation of the STO, which is utilized to sense the magnetization states in a recording layer. The recording layers are designed to have different FMR frequencies so that the FMR excitation is selectively induced by tuning t…
We study current-induced switching in magnetic tunnel junctions (MTJs) in the presence of a field-like spin-transfer torque and titled pinned-layer magnetization in the high current limit at finite temperature. We consider both the Slonczewski and field-like torques with coefficients $a_J$ and $b_J $, respectively. At finite temperatures, $σ= b_J/a_J = \pm1$ leads to a smaller mean switching time compared that with $σ= 0$. The reduction of switching time in the presence of the field-like term is due to the alignment effect (for $σ> 0$) and the initial torque effect.
We demonstrate that the spin Hall effect in a thin film with strong spin-orbit scattering can excite magnetic precession in an adjacent ferromagnetic film. The flow of alternating current through a Pt/NiFe bilayer generates an oscillating transverse spin current in the Pt, and the resultant transfer of spin angular momentum to the NiFe induces ferromagnetic resonance (FMR) dynamics. The Oersted field from the current also generates an FMR signal but with a different symmetry. The ratio of these two signals allows a quantitative determination of the spin current and the spin Hall angle.
Experiments observing spin density and spin currents (responsible for, e.g., spin-transfer torque) in spintronic devices measure only the nonequilibrium contributions to these quantities, typically driven by injecting unpolarized charge current or by applying external time-dependent fields. On the other hand, theoretical approaches to calculate them operate with both the nonequilibrium (carried by electrons around the Fermi surface) and the equilibrium (carried by the Fermi sea electrons) contributions. Thus, an unambiguous procedure should remove the equilibrium contributions, thereby renderi…
We report on first-principles spin-polarised quantum transport calculations (from NEGF+DFT) in MgO-spaced magnetic tunnel junctions (MTJs) based on two different Mn-based Heusler ferrimagnetic metals, namely Mn$_3$Al and Mn$_3$Ga in their tetragonal DO$_{22}$ phase. The former is a fully compensated half-metallic ferrimagnet, while the latter is a low-moment high-spin-polarisation ferrimagnet, both with a small lattice mismatch from MgO. In identical symmetric and asymmetric interface reconstructions across a 3-monolayer thick MgO barrier for both ferrimagets, the linear response (low-voltage)…
We present a study of the magnetic dynamics associated with nanosecond scale magnetic switching driven by the spin Hall effect in 3-terminal nanoscale magnetic tunnel junctions (3T-MTJs) with in-plane magnetization. Utilizing fast pulse measurements in a variety of material stacks and detailed micromagnetic simulations, we demonstrate that this unexpectedly fast and reliable magnetic reversal is facilitated by the self-generated Oersted field, and the short-pulse energy efficiency can be substantially enhanced by micromagnetic curvature in the magnetic free layer. The sign of the Oersted field…
Using a multilayer structure containing (cobalt detector layer)/(copper spacer)/(Permalloy source layer), we show experimentally how the non-reorientable spin-orbit torque generated by the Permalloy source layer (the component of spin-orbit torque that does not change when the Permalloy magnetization is rotated) can be measured using spin-torque ferromagnetic resonance (ST-FMR) with lineshape analysis. We find that dynamic spin pumping between the magnetic layers exerts torques on the magnetic layers as large or larger than the spin-orbit torques, so that if dynamic spin pumping is neglected t…
GaMnAs-based magnetic tunnel junction (MTJ) devices are characterized by in-plane and perpendicular-toplane magnetotransport at low temperatures. Perpendicular-to-plane transport reveals the typical tunneling magnetotransport (TMR) signal. Interestingly, a similar TMR signature is observed in the in-plane transport signal. Here, low-ohmic shunting of the MTJ by the top contact results in significant perpendicular-to-plane current paths. This effect allows the determination of TMR ratios of MTJs based on a simplified in-plane measurement. However, the same effect can lead to an inaccurate deter…
A CMOS-compatible, scalable and compact magnetoelectric spin-torque microwave detector
Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences（中国科学院苏州纳米技术与纳米仿生研究所）；University of Science and Technology of China（中国科学技术大学）；Politecnico di Bari（巴里理工大学）；University of Electronic Science and Technology of China（电子科技大学）；Wuxi University（无锡学院）；King Abdullah University of Science and Technology（阿卜杜拉国王科技大学）
When spin-orbit torques are measured using spin-torque ferromagnetic resonance (ST-FMR), two alternative ways of analyzing the results to extract the torque efficiencies -- lineshape analysis and analysis of the change in linewidth versus DC current -- often give inconsistent results. We identify a source for these inconsistencies. We show that fits of ST-FMR data to the standard analysis framework leave significant residuals that we identify as due to (i) current-induced excitations of a small volume of magnetic material with magnetic damping much larger than the bulk of the magnetic layer, t…
We report an initial experimental survey of spin-Hall torques generated by the rare-earth metals Gd, Dy, Ho, and Lu, along with comparisons to first-principles calculations of their spin Hall conductivities. Using spin torque ferromagnetic resonance (ST-FMR) measurements and DC-biased ST-FMR, we estimate lower bounds for the spin-Hall torque ratio, $ξ_{SH}$, of $\approx$ 0.04 for Gd, $\approx$ 0.05 for Dy, $\approx$ 0.14 for Ho, and $\approx$ 0.014 for Lu. The variations among these elements are qualitatively consistent with results from first principles (density functional theory, DFT, in the…
Future applications of spin-orbit torque will require new mechanisms to improve the efficiency for switching nanoscale magnetic tunnel junctions (MTJs), while also controlling the magnetic dynamics to achieve fast, nanosecond scale performance with low write error rates. Here we demonstrate a strategy to simultaneously enhance the interfacial magnetic anisotropy energy and suppress interfacial spin memory loss by introducing sub-atomic and monatomic layers of Hf at the top and bottom interfaces of the ferromagnetic free layer of an in-plane magnetized three-terminal MTJ device. When combined w…
Current-induced torques in ultrathin Co/Pt bilayers were investigated using an electrically driven FMR technique. The angle dependence of the resonances, detected by a rectification effect as a voltage, were analysed to determine the symmetries and relative magnitudes of the spin-orbit torques. Both anti-damping (Slonczewski) and field-like torques were observed. As the ferromagnet thickness was reduced from 3 to 1 nm, the sign of the field-like torque reversed. This observation is consistent with the emergence of a Rashba spin orbit torque in ultra-thin bilayers.
In the course of searching for promising topological materials for applications in future topological electronics, we evaluated spin-orbit torques (SOTs) in high-quality sputtered $δ-$TaN/Co20Fe60B20 devices through spin-torque ferromagnetic resonance ST-FMR and spin pumping measurements. From the ST-FMR characterization we observed a significant linewidth modulation in the magnetic Co20Fe60B20 layer attributed to the charge-to-spin conversion generated from the $δ-$TaN layer. Remarkably, the spin-torque efficiency determined from ST-FMR and spin pumping measurements is as large as $Θ =$ 0.034…
Spin-torque ferromagnetic resonance (ST-FMR) particularly using magnetic insulators and heavy metals possessing a giant spin Hall effect (SHE) has gotten a lot of attention for the development of spintronic devices. To devise complex functional devices, it is necessary to construct the equivalent spin-circuit representations of different phenomena. Such representation is useful to translate physical equations into circuit elements, benchmarking experiments, and then proposing creative and efficient designs. We utilize the superposition principle in circuit theory to separate the spin Hall magn…
We study whether a direct measurement of the absolute temperature of a Magnetic Tunnel Junction (MTJ) can be performed using the high frequency electrical noise that it delivers under a finite voltage bias. Our method includes quasi-static hysteresis loop measurements of the MTJ, together with the field-dependence of its spin wave noise spectra. We rely on an analytical modeling of the spectra by assuming independent fluctuations of the different sub-systems of the tunnel junction that are described as macrospin fluctuators. We illustrate our method on perpendicularly magnetized MgO-based MTJs…
Spin-polarized charge-currents induce magnetic tunnel junction (MTJ) switching by virtue of spin-transfer-torque (STT). Recently, by taking advantage of the spin dependent thermoelectric properties of magnetic materials, novel means of generating spin-currents from temperature gradients, and their associated thermal spin torques (TSTs) have been proposed, but so far these TSTs have not been large enough to influence MTJ switching. Here we demonstrate significant TSTs in MTJs by generating large temperature gradients across ultrathin MgO tunnel barriers that considerably affect the switching fi…
The role of universal memory can be successfully satisfied by magnetic tunnel junctions (MTJs) where the writing mechanism is based on spin-transfer torque (STT). An improvement in the switching properties (lower switching current density maintaining the thermal stability) has been achieved in MTJs with interfacial perpendicular anisotropy (IPA) at the interface between CoFeB and MgO. In this paper, micromagnetic simulations point out the influence of IPA and saturation magnetization (MS) on the properties of fast magnetization reversal achieved in 5, 10 and 20 ns. Both cases of in-plane and o…
Spintronics is showing promising results in the search for new materials and effects to reduce energy consumption in information technology. Among these materials, ferrimagnets are of special interest, since they can produce large spin currents that trigger the magnetization dynamics of adjacent layers or even their own magnetization. Here, we present a study of the generation of spin current by GdFeCo in a GdFeCo/Cu/NiFe trilayer where the FeCo sublattice magnetization is dominant at room temperature. Magnetic properties such as the saturation magnetization are deduced from magnetometry measu…
Spin pumping is a widely recognized method to generate the spin current in the spintronics, which is acknowledged as a fundamentally dynamic process equivalent to the spin-transfer torque. In this work, we theoretically verify that the oscillating spin current can be pumped from the microwave-motivated breathing skyrmion. The skyrmion spin pumping can be excited by a relatively low frequency compared with the ferromagnetic resonance (FMR) and the current density is larger than the ordinary FMR spin pumping. Based on the skyrmion spin pumping, we build a high reading-speed racetrack memory mode…
Since the discovery of the spin orbit torque (SOT) induced by spin Hall effect in heavy metals, much effort has been devoted to understanding the mechanism of the charge-to-spin conversion as well as to developing new schemes for high speed, low energy magnetic recording technologies. While fast switching has been demonstrated in three terminal magnetic tunnel junctions (3T-MTJs) through applying short voltage pulses in the heavy metal channel, detailed understanding of the switching mechanism is lacking due to the complexity of the multi-layered magnetic structure and the three-terminal geome…
