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An opto-electronic readout of the memory state in spin transfer torque random access memory (STT-RAM) cells is proposed. A single optical beam illuminating an array of STT-RAM cells creates electrical potential along each STT-RAM cell due to optical rectification that can be further enhanced through plasmon drag effect (PLDE). Then, the photo-induced voltage is assumed to be measured by conventional electronics. Here, a theoretical modeling is performed, where the results provide an estimate of the photo-induced voltage in each memory cell and its variation with respect to the changes in state of the memory cell (parallel vs anti-parallel). Our study shows that the plasmonic enhancement facilitates ${\sim }$ 20 times enhancement in the voltage change due to state change of the each memory cell, compared to the case of out-of-resonance excitation. This enhancement potentially improves the memory readout rate if a proper supporting electronic circuit is available.

The ability to control and tune magnetic dissipation is a key concept of emergent spintronic technologies. Magnon scattering processes constitute a major dissipation channel in nanomagnets, redefine their response to spin torque, and hold the promise for manipulating magnetic states on the quantum level. Controlling these processes in nanomagnets, while being imperative for spintronic applications, has remained difficult to achieve. Here, we propose an approach for controlling magnon scattering by a switch that generates nonuniform magnetic field at nanoscale. We provide an experimental demonstration in magnetic tunnel junction nanodevices, consisting of a free layer and a synthetic antiferromagnet. By triggering the spin-flop transition in the synthetic antiferromagnet and utilizing its stray field, magnon interaction in the free layer is toggled. The results open up avenues for tuning nonlinearities in magnetic neuromorphic applications and for engineering coherent magnon coupling in hybrid quantum information technologies.

A single resonance-type spin-torque microwave diode (STMD) can be used as a quadratic detector to determine the frequency $f$ of an external microwave signal when the power $P_{\rm rf}$ of this signal is known. However, unless the signal's frequency $f$ exactly coincides with the detector's resonance frequency $f_{\rm res}$ , there exists a finite frequency determination error $\Delta f$ . In this letter, we show theoretically and experimentally that if a pair of independent STMDs with different resonance frequencies connected in parallel is used for the signal frequency determination, knowledge of the signal power is not necessary, and the frequency determination error can be substantially reduced to $\Delta f \approx $ 30 MHz at the frequency of $f \approx $ 5.0 GHz.

Frequency conversion forms an integral block of the electronic circuits used in various applications including energy harvesting, communications and signal processing. These frequency conversion units however require external power sources and occupy a large device footprint making it difficult to be integrated in micro-circuits. Here we demonstrate that nanoscale magnetic tunnel junctions can act as frequency converters without an external power supply or DC bias source. The device directly mixes an external microwave signal with the internal spin precession oscillations to create new frequencies tunable by an external magnetic field in a single device with a small device footprint. We observe up-conversion and down-conversion of the input signal for excitation frequencies between 2 GHz and 6 GHz. We also show that the device acts as a zero-bias rectifier that can generate voltages exceeding 12 mV when the excitation frequency matches the natural oscillations mode of the device.

Action potentials are the basic unit of information in the nervous system, and their reliable detection and decoding holds the key to understanding how the brain generates complex thought and behavior. Transduction of these signals into microwave signal oscillations can enable wireless sensors that report on brain activity through magnetic induction. In this letter, we demonstrate that action potentials from the lateral giant neurons of crayfish can induce microwave oscillations in nanoscale magnetic tunnel junctions (NMTJs). We show that action potentials activate microwave oscillations in NMTJs with an amplitude that follows the action potential signal, demonstrating that the device has both the sensitivity and temporal resolution to respond to action potentials from a single neuron. The activation of magnetic oscillations by action potentials, together with the small surface area and the high-frequency tunability, makes these devices potential candidates for high-resolution sensing of bioelectric signals from neural tissues. These device attributes may be useful for the design of high-throughput bidirectional brain–machine interfaces.

An optoelectronic readout method for reading the state of STT-RAM cells based on plasmon drag effect is proposed. Our simulations show that the proposed scheme can achieve up to 29.6 Gbit/sec readout speed.

Long-range spin transport in magnetic systems can be achieved by means of exchange-mediated spin textures with robust topological winding - a phenomenon referred to as spin superfluidity. Its experimental signatures have been discussed in antiferromagnets which are nearly free of dipolar interaction. In ferromagnets, which present with non-negligible dipole fields, however, realization of such spin transport has remained a challenge. Using micromagnetic simulations, we investigate exchange-mediated spin transport in extended thin ferromagnetic films. We uncover a two-fluidstate, in which the long-range spin transport by spin textures co-exists with and is stabilized by spin waves, as well as a soliton-screened spin transport regime at high spin injection biases. Both states are associated with distinct spin texture reconstructions near the spin injection region and sustain spin transport over large distances.

Spin-orbit torque nano-oscillators based on bilayers of ferromagnetic and nonmagnetic metals are ultra-compact current-controlled microwave signal sources. They are attractive for practical applications such as microwave assisted magnetic recording, neuromorphic computing, and chip-to-chip wireless communications. However, a major drawback of these devices is low output microwave power arising from the relatively small anisotropic magnetoresistance of the ferromagnetic layer. Here we experimentally show that the output power of a spin-orbit torque nano-oscillator can be significantly enhanced without compromising its structural simplicity. Addition of a ferromagnetic reference layer to the oscillator allows us to employ current-in-plane giant magnetoresistance to boost the output power of the device. This enhancement of the output power is a result of both large magnitude of giant magnetoresistance compared to that of anisotropic magnetoresistance and their different angular dependencies. Our results hold promise for practical applications of spin-orbit torque nano-oscillators. Spin-orbit torque driven oscillators, such as spin Hall oscillators, form a class of devices that are intensively studied due to potential practical applications in spintronics. Here, the authors modify the conventional ferromagnetic/nonmagnetic stack to include an additional ferromagnetic layer and leverage the giant magnetoresistance effect to enhance the direct conversion of an in-plane driving current into the microwave output signal.

Nanoscale magnets are the building blocks of many existing and emergent spintronic applications, e.g. nonvolatile spin torque memory, spin torque oscillators, neuromorphic and probabilistic computing. Controlling magnetic damping in nanomagnets holds the key to improving the performance of future technologies. Here, we experimentally demonstrate and theoretically corroborate that a ferromagnetic nano-particle (free layer of a magnetic tunnel junction (MTJ) nanopillar) can exhibit spin dynamics qualitatively different from those predicted by the harmonic oscillator model. Nonlinear contributions to the damping can be unusually strong, and the effective damping parameter itself can exhibit resonant dependence on field/frequency [1].

The discovery of interfacial Dzyaloshinskii-Moriya interaction (DMI) enables development of novel ultra-compact non-reciprocal devices for microwave signal processing. Such devices are based on control of spin waves and magneto-elastic waves by electric field and addition of ultra-thin layers of heavy metals to the devices. Here we discuss recent advances in the development of such systems, which can be used for implementation of on-chip non-reciprocal microwave devices.

Spin transfer torque magnetic random access memory (STT-MRAM) is a promising candidate for next generation memory as it is non-volatile, fast, and has unlimited endurance. Another important aspect of STT-MRAM is that its core component, the nanoscale magnetic tunneling junction (MTJ), is thought to be radiation hard, making it attractive for space and nuclear technology applications. However, studies on the effects of ionizing radiation on the STT-MRAM writing process are lacking for MTJs with perpendicular magnetic anisotropy (pMTJs) required for scalable applications. Particularly, the question of the impact of extreme total ionizing dose on perpendicular magnetic anisotropy, which plays a crucial role on thermal stability and critical writing current, remains open. Here we report measurements of the impact of high doses of gamma and neutron radiation on nanoscale pMTJs used in STT-MRAM. We characterize the tunneling magnetoresistance, the magnetic field switching, and the current-induced switching before and after irradiation. Our results demonstrate that all these key properties of nanoscale MTJs relevant to STT-MRAM applications are robust against ionizing radiation. Additionally, we perform experiments on thermally driven stochastic switching in the gamma ray environment. These results indicate that nanoscale MTJs are promising building blocks for radiation-hard non-von Neumann computing.

Spin–orbit torques (SOTs) in multilayers of ferromagnetic (FM) and non-magnetic (NM) metals can manipulate the magnetization of the FM layer efficiently. This is employed, for example, in non-volatile magnetic memories for energy-efficient mobile electronics1,2 and spin torque nano-oscillators3–7 for neuromorphic computing8. Recently, spin torque nano-oscillators also found use in microwave-assisted magnetic recording, which enables ultrahigh-capacity hard disk drives9. Most SOT devices employ spin Hall10,11 and Rashba12 effects, which originate from spin–orbit coupling within the NM layer and at the FM/NM interfaces, respectively. Recently, SOTs generated by the anomalous Hall effect in FM/NM/FM multilayers were predicted13 and experimentally realized14. The control of SOTs through crystal symmetry was demonstrated as well15. Understanding all the types of SOTs that can arise in magnetic multilayers is needed for a formulation of a comprehensive SOT theory and for engineering practical SOT devices. Here we show that a spin-polarized electric current known to give rise to anisotropic magnetoresistance (AMR) and the planar Hall effect (PHE) in a FM16 can additionally generate large antidamping SOTs with an unusual angular symmetry in NM1/FM/NM2 multilayers. This effect can be described by a recently proposed magnonic mechanism17. Our measurements reveal that this torque can be large in multilayers in which both spin Hall and Rashba torques are negligible. Furthermore, we demonstrate the operation of a spin torque nano-oscillator driven by this SOT. These findings significantly expand the class of materials that exhibit giant SOTs. A spin-polarized current responsible for the planar Hall effect and anisotropic magnetoresistance is found to generate large antidamping spin–orbit torque in normal metal/ferromagnet/normal metal trilayers.

Spin waves propagating in nanoscale ferromagnetic waveguides are considered promising for a new generation of digital and analog magnonic signal-processing devices, where the signal is encoded in a spin wave's amplitude or phase, or both. Stable, error-free operation of spin-wave devices requires well-defined spin-wave phase, which can be disrupted by technological imperfections or thermal noise, leading to the accumulation of phase errors in a magnonic circuit. The authors demonstrate that such phase errors can be corrected by the application of parametric pumping, via voltage-controlled magnetic anisotropy, to local gates placed in the spin wave's path.

Yttrium iron garnet (YIG) is a material with unique properties that make it very attractive for use in microwave applications, such as frequency-selective limiters and logic processing. However, the decay of a spin wave's amplitude as it propagates in the material curbs the use of YIG in practical applications. To surmount this limitation, in this study the surface spin currents of a topological insulator are used to enhance the spin-wave amplitude in adjacent YIG. In addition, interesting properties of magnons are observed and investigated, to advance spintronics.

Nonlinear magnon scattering redefines how nanomagnets respond to spin currents., Magnetic damping is a key metric for emerging technologies based on magnetic nanoparticles, such as spin torque memory and high-resolution biomagnetic imaging. Despite its importance, understanding of magnetic dissipation in nanoscale ferromagnets remains elusive, and the damping is often treated as a phenomenological constant. Here, we report the discovery of a giant frequency-dependent nonlinear damping that strongly alters the response of a nanoscale ferromagnet to spin torque and microwave magnetic field. This damping mechanism originates from three-magnon scattering that is strongly enhanced by geometric confinement of magnons in the nanomagnet. We show that the giant nonlinear damping can invert the effect of spin torque on a nanomagnet, leading to an unexpected current-induced enhancement of damping by an antidamping torque. Our work advances the understanding of magnetic dynamics in nanoscale ferromagnets and spin torque devices.

Competition between superconducting and ferromagnetic ordering at interfaces between ferromagnets (F) and superconductors (S) gives rise to several proximity effects such as odd-triplet superconductivity and spin-polarized supercurrents. A prominent example of an S/F proximity effect is the spin switch effect (SSE) observed in S/F/N/F superconducting spin-valve multilayers, in which the superconducting transition temperature T$_c$ is controlled by the angle $\phi$ between the magnetic moments of the F layers separated by a nonmagnetic metallic spacer N. Here we present an experimental study of SSE in Nb/Co/Cu/Co/CoO$_x$ nanowires measured as a function of bias current flowing in the plane of the layers. These measurements reveal an unexpected dependence of T$_c(\phi)$ on the bias current: T$_c(\pi)$--T$_c(0)$ changes sign with increasing current bias. We attribute the origin of this bias dependence of the SSE to a spin Hall current flowing perpendicular to the plane of the multilayer, which suppresses T$_c$ of the multilayer. The bias dependence of SSE can be important for hybrid F/S devices such as those used in cryogenic memory for superconducting computers as device dimensions are scaled down to the nanometer length scale., Comment: 6 pages, 3 figures

A broadband spintronic diode would be important for electromagnetic energy harvesting, with the advantages of nanoscale size and low output resistance. This study gives experimental proof of broadband microwave detection in a magnetic tunnel junction, with a spintronic diode providing sufficient dc voltage to supply a low-power nanodevice. Such diodes also work as rectifiers below 1 nW, outperforming traditional Schottky diodes. These results point to spintronic diodes as building blocks in self-powered systems such as implantable biomedical devices, wireless sensors, and portable electronics, plus ultralow-power detectors for aerospace applications and the ``Internet of Things''.

Energy-efficient switching of magnetization is a central problem in nonvolatile magnetic storage and magnetic neuromorphic computing. In the past two decades, several efficient methods of magnetic switching were demonstrated including spin torque, magneto-electric, and microwave-assisted switching mechanisms. Here we experimentally show that low-dimensional magnetic chaos induced by alternating spin torque can strongly increase the rate of thermally-activated magnetic switching in a nanoscale ferromagnet. This mechanism exhibits a well-pronounced threshold character in spin torque amplitude and its efficiency increases with decreasing spin torque frequency. We present analytical and numerical calculations that quantitatively explain these experimental findings and reveal the key role played by low-dimensional magnetic chaos near saddle equilibria in enhancement of the switching rate. Our work unveils an important interplay between chaos and stochasticity in the energy assisted switching of magnetic nanosystems and paves the way towards improved energy efficiency of spin torque memory and logic., Energy-efficient manipulation of spins at the nanoscale can advance magnetic storage and computing technologies. Here the authors show that low-dimensional chaos generated by alternating spin torque can induce magnetic switching in a nanoscale ferromagnet.

Non-collinear spin ground states in metallic antiferromagnets can give rise to anomalous Hall effect, which enables magnetic state readout in antiferromagnetic spintronic devices. Here we report growth of highly textured films of a non-collinear antiferromagnet IrMn3 on MgO(111) substrates by magnetron sputtering. The films consist of epitaxial (111) twin domains rotated by 60 degrees within the film plane. The films exhibit partial L12 ordering that supports the non-collinear T1 spin structure predicted to give rise to anomalous Hall effect. An MgO buffer layer evaporated onto the substrate increases the L12 order parameter from 0.4 to 0.75 but destroys the (111) crystallographic texture.

Beyond-CMOS devices concepts are greatly dependent on new functional materials to provide inspiration and innovation beyond the silicon status quo. Here, we propose a material framework specifically for beyond-CMOS devices. In doing so, material system examples and data points presented are taken from the Center on Functional Accelerated Nanomaterials Engineering, the STARnet Center of Excellence.

The magnesium oxide (MgO) adhesion layer is proposed to avoid adverse effects of lossy metallic adhesion layers in thin film plasmonic nanostructures. Such adverse effects can be in the form of resonance broadening and a decrease in the resonance magnitude. We fabricate and test the quality of MgO adhesion layers and determine its optical properties through ellipsometry measurements. We also provide the plasmonic response of various plasmonic nanostructures (nanohole array, nanodisk array, dimer nanohole array, and bowtie slot antenna array) with a MgO adhesion layer and conventional adhesion layers including titanium (Ti), chromium (Cr), tantalum (Ta), and indium tin oxide (ITO). Our results show that unlike conventional adhesives, MgO has almost no adverse effect on the plasmonic resonance of the designed nanostructures.

Two easy-plane ferromagnetic layers, antiferromagnetically coupled through a thin nonmagnetic metal layer, form the magnetic analog of a Josephson junction. A current driven spin chemical potential drives a 2 π precession of the in-plane magnetization of each ferromagnet. The participation of the full magnetic moment in the 2 π precession maximizes the giant magnetoresistance and the ac output power. The frequency can be continuously tuned by a dc bias. An applied ac bias results in a time-averaged magnetoresistance with Shapiro-like steps. The multistate mode-locking behavior exhibited by the Shapiro steps may be exploited for applications such as microwave detectors and neuromorphic computing. They may also serve as an experimental signature of spin superfluidity.

Rectification is an important stage in electronic circuits for any wireless radio frequency power transfer application. Currently, Schottky diodes are widely used as rectifiers; however, they are inefficient at low power levels of microwatts or less (providing maximum sensitivities around 4 mV/μW). Nanoscale magnetic tunnel junctions can serve as alternative rectifiers by utilizing the so-called spin-torque diode effect, demonstrating a much higher rectification sensitivity (200 mV/μW) compared to Schottky diodes. However, for this mechanism to work, the signal frequency must match the ferromagnetic resonance frequency, which typically lies in the gigahertz range. For signals in the megahertz range or lower, Schottky diodes remain the only option for rectification. Here, we demonstrate a mechanism based on thermally activated adiabatic stochastic resonance in magnetic tunnel junctions to produce low frequency (up to tens of megahertz) signal rectification at low input power (submicrowatt), with a sensitivity of up to 35 mV/μW—higher than state-of-the-art Schottky diode rectifiers at this frequency and power range. These findings suggest magnetic tunnel junctions as potential alternatives to Schottky diodes for low frequency and low power applications.

The design of modern circulators and isolators relies on nonreciprocal (discriminating forward and backward wave vectors, breaking time-reversal symmetry) electromagnetic waves in magnetic materials. Creating such devices that are small enough for portable electronics (think mobile phones) remains challenging. The authors show theoretically the nonreciprocal propagation of surface acoustic waves in multilayers with simultaneous magnetoelastic and Dzyaloshinskii-Moriya interactions. Despite both interactions being relatively weak, their interplay creates up to 45 dB of isolation for counterpropagating waves, making these multilayers promising for miniaturized rf isolators.

A spintronic method of ultra-fast broadband microwave spectrum analysis is proposed. It uses a rapidly tuned spin torque nano-oscillator (STNO), and does not require injection locking. This method treats an STNO generating a microwave signal as an element with an oscillating resistance. When an external signal is applied to this "resistor" for analysis, it is mixed with the signal generated by the STNO. The resulting mixed voltage contains the "sum" and "difference" frequencies, and the latter produces a DC component when the external frequency matches the frequency generated by the STNO. The mixed voltage is processed using a low pass filter to exclude the "sum" frequency components, and a matched filter to exclude the dependence of the resultant DC voltage on the phase difference between the two signals. It is found analytically and by numerical simulation, that the proposed spectrum analyzer has a frequency resolution at a theoretical limit in a real-time scanning bandwidth of 10~GHz, and a frequency scanning rate above 1~GHz/ns, while remaining sensitive to signal power as low as the Johnson-Nyquist thermal noise floor., 5 pages, 4 figures

We experimentally study nanowire-shaped spin-Hall nano-oscillators based on nanometer-thick epitaxial films of Yttrium Iron Garnet grown on top of a layer of Pt. We show that, although these films are characterized by significantly larger magnetic damping in comparison with the films grown directly on Gadolinium Gallium Garnet, they allow one to achieve spin current-driven auto-oscillations at comparable current densities, which can be an indication of the better transparency of the interface to the spin current. These observations suggest a route for improvement of the flexibility of insulator-based spintronic devices and their compatibility with semiconductor technology.

Spin Hall oscillators (SHO) are promising candidates for the generation, detection and amplification of high frequency signals, that are tunable through a wide range of operating frequencies. They offer to be read out electrically, magnetically and optically in combination with a simple bilayer design. Here, we experimentally study the spatial dependence and spectral properties of auto-oscillations in SHO devices based on Pt(7 nm)/\ Ni$_{\mathrm{80}}$Fe$_{\mathrm{20}}$(5 nm) tapered nanowires. Using Brillouin light scattering microscopy, we observe two individual self-localized spin-wave bullets that oscillate at two distinct frequencies (5.2 GHz and 5.45 GHz) and are localized at different positions separated by about 750 nm within the SHO. This state of a tapered SHO has been predicted by a Ginzburg-Landau auto-oscillator model, but not yet been directly confirmed experimentally. We demonstrate that the observed bullets can be individually synchronized to external microwave signals, leading to a frequency entrainment, linewidth reduction and increase in oscillation amplitude for the bullet that is selected by the microwave frequency. At the same time, the amplitude of other parasitic modes decreases, which promotes the single-mode operation of the SHO. Finally, the synchronization of the spin-wave bullets is studied as a function of the microwave power. We believe that our findings promote the realization of extended spin Hall oscillators accomodating several distinct spin-wave bullets, that jointly cover an extended range of tunability.

Many spintronics applications consist of ultrathin magnetic and nonmagnetic multilayers and require an in-depth understanding of interfacial magnetism and spin transport. Here, we study permalloy/copper/platinum multilayer systems. We find that magnetic damping, perpendicular anisotropy, and proximity magnetization exhibit correlated oscillations as a function of the copper thickness. We ascribe these observations to an oscillatory interlayer coupling between permalloy and platinum. Such interlayer coupling may have a significant impact on the performance of spintronics applications.

The brain is a complex network of interconnected circuits that exchange electrical signals with each other. These electrical signals provide insight on how neural circuits code information, and give rise to sensations, thoughts, emotions and actions. Currents methods to detect and modulate these electrical signals use implanted electrodes or optical fields with light sensitive dyes in the brain. These techniques require complex surgeries or suffer low resolution. In this talk we explore a new method to both image and stimulate single neurons using spintronics. We propose using a Spin Transfer Nano-Oscillators (STNOs) as a nanoscale sensor that converts neuronal action potentials to microwave field oscillations that can be detected wirelessly by magnetic induction. We will describe our recent proof-of-concept demonstration of both detection and wireless modulation of neuronal activity using STNOs. For detection we use electrodes to connect a STNO to a lateral giant crayfish neuron. When we stimulate the neuron, the STNO responds to the neuronal activity with a corresponding microwave signal. For modulation, we stimulate the STNOs wirelessly using an inductively coupled solenoid. The STNO rectifies the induced microwave signal to produce a direct voltage. This direct voltage from the STNO, when applied in the vicinity of a mammalian neuron, changes the frequency of electrical signals produced by the neuron.

Plasmonic nanostructures are highly used for sensing purposes since they support plasmonic modes which make them highly sensitive to the refractive index change of their surrounding medium. Therefore, they can also be used to detect changes in optical properties of ultrathin layer films in a multilayer plasmonic structure. Here, we investigate the changes in optical properties of ultrathin films of macro structures consisting of STT-RAM layers. Among the highest sensitive plasmonic structures, nanohole array has attracted many research interest because of its ease of fabrication, small footprint, and simplified optical alignment. Hence it is more suitable for defect detection in STT-RAM geometries. Moreover, the periodic nanohole pattern in the nanohole array structure makes it possible to couple the light to the surface plasmon polariton (SPP) mode supported by the structure. To assess the radiation damages and defects in STT-RAM cells we have designed a multilayer nanohole array based on the layers used in STT-RAM structure, consisting 4nm- Ta/1.5nm-CoFeB/2nm-MgO/1.5nm-CoFeB/4nm-Ta layers, all on a 300nm silver layer on top of a PEC boundary. The nanoholes go through all the layers and become closed by the PEC boundary on one side. The dimensions of the designed nanoholes are 313nm depth, 350nm diameter, and 700nm period. Here, we consider the normal incidence of light and investigate zeroth-order reflection coefficient to observe the resonance. Our simulation results show that a 10% change in refractive index of the 2nm-thick MgO layer leads to about 122GHz shift in SPP resonance in reflection pattern.

The spin-orbit interactions in heavy-metal/ferromagnet heterostructures have attracted considerable attention because they provide an efficient way to manipulate the magnetization with strong current-driven spin-orbit torques (SOTs) via the spin Hall effect in the heavy metal or Rashba effect due to the symmetry breaking at the interface. Theoretical calculations predict no dependence of the SOTs on the out-of-plane angle of magnetization due to spin Hall effect, but Rashba effect induces a nontrivial angular dependence of SOTs. Quantitative measurements with adiabatic harmonic Hall technique have observed the angular dependence in Ta/CoFeB/MgO or $\mathrm{Pt}/\mathrm{Co}/\mathrm{Al}{\mathrm{O}}_{\mathrm{x}}$ with perpendicular magnetic anisotropy. However, this method is complicated because the signal consists of both anomalous and planar Hall contributions. In addition, the fitting of the measurement data is sensitive to the fitting parameters, particularly to the perpendicular anisotropy, in a certain angle region (40--70\ifmmode^\circ\else\textdegree\fi{}). To avoid this uncertainty, we have developed a scheme to quantify the angular dependence of SOTs based on the magneto-optic Kerr effect with field calibration. Without fitting procedures, we precisely determine the SOTs and their angle dependence on the magnetization orientation. We observe a strong angular dependence that is different from the previous experimental observations. Based on this strong dependence, we conclude that a Rashba effect at the same interface, that is responsible for the perpendicular magnetic anisotropy, is the dominant mechanism for the current-driven SOTs in this system.

This article reviews static and dynamic interfacial effects in magnetism, focusing on interfacially-driven magnetic effects and phenomena associated with spin-orbit coupling and intrinsic symmetry breaking at interfaces. It provides a historical background and literature survey, but focuses on recent progress, identifying the most exciting new scientific results and pointing to promising future research directions. It starts with an introduction and overview of how basic magnetic properties are affected by interfaces, then turns to a discussion of charge and spin transport through and near interfaces and how these can be used to control the properties of the magnetic layer. Important concepts include spin accumulation, spin currents, spin transfer torque, and spin pumping. An overview is provided to the current state of knowledge and existing review literature on interfacial effects such as exchange bias, exchange spring magnets, spin Hall effect, oxide heterostructures, and topological insulators. The article highlights recent discoveries of interface-induced magnetism and non-collinear spin textures, non-linear dynamics including spin torque transfer and magnetization reversal induced by interfaces, and interfacial effects in ultrafast magnetization processes., 193 pages, including 28 figures inserted after text and references. Paper accepted in Reviews of Modern Physics

A spin-torque nano-oscillator (STNO) driven by a ramped bias current can perform spectrum analysis quickly over a wide frequency bandwidth. The STNO spectrum analyzer operates by injection locking to external microwave signals and produces an output DC voltage $V_{\rm dc}$ that temporally encodes the input spectrum. We found, via numerical analysis with a macrospin approximation, that an STNO is able to scan a $10~\rm GHz$ bandwidth in less than $100~\rm ns$ (scanning rate $R$ exceeds $100~\rm MHz/ns$). In contrast to conventional quadratic microwave detectors, the output voltage of the STNO analyzer is proportional to the amplitude of the input microwave signal $I_{\rm rf}$ with sensitivity $S = dV_{\rm dc}/dI_{\rm rf} \approx 750~\rm mV/mA$. The minimum detectable signal of the analyzer depends on the scanning rate $R$ and, at low $R \approx 1~\rm MHz/ns$, is about $1~\rm pW$., Comment: 5 pages, 5 figures

Energy loss due to ohmic heating is a major bottleneck limiting down-scaling and speed of nano-electronic devices, and harvesting ohmic heat for signal processing is a major challenge in modern electronics. Here, we demonstrate that thermal gradients arising from ohmic heating can be utilized for excitation of coherent auto-oscillations of magnetization and for generation of tunable microwave signals. The heat-driven dynamics is observed in Y3Fe5O12/Pt bilayer nanowires where ohmic heating of the Pt layer results in injection of pure spin current into the Y3Fe5O12 layer. This leads to excitation of auto-oscillations of the Y3Fe5O12 magnetization and generation of coherent microwave radiation. Our work paves the way towards spin caloritronic devices for microwave and magnonic applications., Harvesting ohmic heat for signal processing is one of major challenges in modern electronics and spin caloritronics, but not yet well accomplished. Here the authors demonstrate a spin torque oscillator device driven by pure spin current arising from thermal gradient across an Y3Fe5O12/Pt interface.

A dimer nanohole array is proposed for in situ characterization of radiation damages in spin transfer torque random access memory (STT-RAM) multilayer structures. The structure supports a Fano resonance, which is about twice as sensitive to the refractive index changes in the surface layer, compared to the plasmonic mode in single nanohole arrays. A simplified STT-RAM multilayer of air/gold(5 nm)/MgO(10 nm)/gold(60 nm)/quartz substrate is considered as the platform for the dimer nanohole array. Our studies show that regarding the changes in the ultrathin MgO layer, the normalized figure of merit for this structure is up to more than 10 times larger than an array of single nanoholes. Furthermore, an improvement in bulk sensing performance over the array of nanohole heptamers is observed.

We report the experimental demonstration of a magnetologic gate built on graphene at room temperature. This magnetologic gate consists of three ferromagnetic electrodes contacting a single layer graphene spin channel and relies on spin injection and spin transport in the graphene. We utilize electrical bias tuning of spin injection to balance the inputs and achieve "exclusive or" (XOR) logic operation. Furthermore, simulation of the device performance shows that substantial improvement towards spintronic applications can be achieved by optimizing device parameters such as device dimensions. This advance holds promise as a basic building block for spin-based information processing., Comment: 23 pages, 4 figures

Microwave detectors based on the spin-torque diode effect are among the key emerging spintronic devices. By utilizing the spin of electrons in addition to charge, they have the potential to overcome the theoretical performance limits of their semiconductor (Schottky) counterparts. However, so far, practical implementations of spin-diode microwave detectors have been limited by the necessity to apply a magnetic field. Here, we demonstrate nanoscale magnetic tunnel junction microwave detectors, exhibiting high-detection sensitivity of 75,400 mV mW−1 at room temperature without any external bias fields, and for low-input power (micro-Watts or lower). This sensitivity is significantly larger than both state-of-the-art Schottky diode detectors and existing spintronic diodes. Micromagnetic simulations and measurements reveal the essential role of injection locking to achieve this sensitivity performance. This mechanism may provide a pathway to enable further performance improvement of spin-torque diode microwave detectors., Nanomagnetic materials allow for the emission and detection of microwave radiation in technological applications by spin excitation. Here, the authors present sensitive room-temperature microwave detectors based on nanoscale magnetic tunnel junctions, enabled via spin torque and injection locking.

We study perpendicular magnetic anisotropy in thin films of Ta/Co20Fe60B20/MgO by ferromagnetic resonance and find a linear temperature dependence for the first and second order uniaxial terms from 5 to 300 K. Our data suggest the possible hybridization of Fe-O orbitals at the CoFeB/MgO interface for the origin of the first order anisotropy. However, we also find that non-interfacial contributions to the anisotropy are present. An easy-cone anisotropy is found for the entire temperature range in the narrow region of film thicknesses around the spin reorientation transition 1.2–1.35 nm.

Manipulation of magnetization by electric field is a central goal of spintronics because it enables energy-efficient operation of spin-based devices. Spin wave devices are promising candidates for low-power information processing, but a method for energy-efficient excitation of short-wavelength spin waves has been lacking. Here we show that spin waves in nanoscale magnetic tunnel junctions can be generated via parametric resonance induced by electric field. Parametric excitation of magnetization is a versatile method of short-wavelength spin wave generation, and thus, our results pave the way toward energy-efficient nanomagnonic devices.

We present a seamless integration of spin-based memory and logic circuits. The building blocks are magnetologic gates based on a hybrid graphene/ferromagnet material system. We use network search engines as a technology demonstration vehicle and simulate a high-speed, small-area, and low-power spin-based circuit.

Transfer of angular momentum from a spin-polarized current to a ferromagnet provides an efficient means to control the dynamics of nanomagnets. A peculiar consequence of this spin-torque, the ability to induce persistent oscillations of a nanomagnet by applying a dc current, has previously been reported only for spatially uniform nanomagnets. Here we demonstrate that a quintessentially nonuniform magnetic structure, a magnetic vortex, isolated within a nanoscale spin valve structure, can be excited into persistent microwave-frequency oscillations by a spin-polarized dc current. Comparison to micromagnetic simulations leads to identification of the oscillations with a precession of the vortex core. The oscillations, which can be obtained in essentially zero magnetic field, exhibit linewidths that can be narrower than 300 kHz, making these highly compact spin-torque vortex oscillator devices potential candidates for microwave signal-processing applications, and a powerful new tool for fundamental studies of vortex dynamics in magnetic nanostructures., 14 pages, 4 figures

International audience; We study thin films and magnetic tunnel junction nanopillars based on Ta/Co20Fe60B20/MgO multilayers by electrical transport and magnetometry measurements. These measurements suggest that an ultrathin magnetic oxide layer forms at the Co20Fe60B20/MgO interface. At approximately 160 K, the oxide undergoes a phase transition from an insulating antiferromagnet at low temperatures to a conductive weak ferromagnet at high temperatures. This interfacial magnetic oxide is expected to have significant impact on the magnetic properties of CoFeB-based multilayers used in spin torque memories. (C) 2015 AIP Publishing LLC.

We report experimental and theoretical studies of spin wave eigenmodes in transversely magnetized thin film Permalloy wires. Using broadband ferromagnetic resonance technique, we measure the spectrum of spin wave eigenmodes in individual wires as a function of magnetic field and wire width. Comparison of the experimental data to our analytical model and micromagnetic simulations shows that the intrinsic dipolar edge pinning of spin waves is negligible in transversely magnetized wires. Our data also quantify the degree of extrinsic edge pinning in Permalloy wires. This work establishes the boundary conditions for dynamic magnetization in transversely magnetized thin film wires for the range of wire widths and thicknesses studied, and provides a quantitative description of the spin wave eigenmode frequencies and spatial profiles in this system as a function of the wire width.

We present time-resolved measurements of gigahertz-scale magnetic dynamics caused by torque from a spin-polarized current. By working in the time domain, we determined the motion of the magnetic moment throughout the process of spin-transfer–driven switching, and we measured turn-on times of steady-state precessional modes. Time-resolved studies of magnetic relaxation allow for the direct measurement of magnetic damping in a nanomagnet and prove that this damping can be controlled electrically using spin-polarized currents.

This letter presents a diode-magnetic tunnel junction (MTJ) magnetic random access memory cell in a 65-nm complimentary metal-oxide-semiconductor compatible process. A voltage-controlled magnetic anisotropy switching mechanism, in addition to STT, allows for a unipolar set/reset write scheme, where voltage pulses of the same polarity, but different amplitudes, are used to switch the MTJs. A small crossbar array is constructed from 65-nm MTJs fabricated on a silicon wafer, with switching voltages ~ 1 V and thermal stability greater than 10 years, with discrete germanium diodes as access devices to allow for read/write operations. The crossbar architecture can be extended to multiple layers to create a 3-D stackable, nonvolatile memory with a sub-1F2 effective cell size.

We studied the spin transfer torque (STT) driven switching voltage distribution systematically by characterizing the switching probability density function (PDF) with large statistics (105 trials) across a wide time scale from 5 ns to 1 μs. The skew normal distribution function is found to be a good one to fit the measured switching PDF down to low values, which would be used as a guideline to extrapolate read disturb rate (RDR) and write error rate (WER) in STT-RAM design. Moreover, the asymmetry of switching probability density function is observed to flip when the pulse width decreases. It is related to the fluctuation mechanism transition from the thermal agitation to the initial magnetization trajectory dispersion.

This letter presents energy-efficient MgO based magnetic tunnel junction (MTJ) bits for high-speed spin transfer torque magnetoresistive random access memory (STT-MRAM). We present experimental data illustrating the effect of device shape, area, and tunnel-barrier thickness of the MTJ on its switching voltage, thermal stability, and energy per write operation in the nanosecond switching regime. Finite-temperature micromagnetic simulations show that the write energy changes with operating temperature. The temperature sensitivity increases with increasing write pulsewidth and decreasing write voltage. We demonstrate STT-MRAM cells with switching energies of