Search NASA⌕ Search

SEARCH · Search NASA

Results for “spin torque”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Resolving Discrepancies in Spin-Torque Ferromagnetic Resonance Measurements: Lineshape versus Linewidth Analyses

When spin-orbit torques are measured using spin-torque ferromagnetic resonance, two alternative ways of analyzing the results to extract the torque efficiencies—lineshape analysis and analysis of the change in linewidth versus direct current—often give inconsistent results. We identify a source for these inconsistencies. We show that fits of spin-torque ferromagnetic resonance 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 that of the bulk of the magnetic layer, which we speculate is associated with the heavy-metal–magnet interface and (ii) oscillations of the sample magnetization at the modulation frequency due to heating. Here, the dependence of the residual signals on direct current can interfere with an accurate extraction of spin-torque efficiencies by the linewidth method. We show that the discrepancies between the two types of analysis can be largely eliminated by extrapolation of the window of magnetic fields used in the linewidth fits to small values so as to minimize the influence of the residual signals.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Self-oscillation in spin torque oscillator stabilized by field-like torque

The effect of the field-like torque on the self-oscillation of the magnetization in spin torque oscillator with a perpendicularly magnetized free layer was studied theoretically. A stable self-oscillation at zero field is excited for negative β while the magnetization dynamics stops for β = 0 or β > 0, where β is the ratio between the spin torque and the field-like torque. The reason why only the negative β induces the self-oscillation was explained from the view point of the energy balance between the spin torque and the damping. The oscillation power and frequency for various β were also studied by numerical simulation.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Frequency control of a spin-torque oscillator using magnetostrictive anisotropy

We report the working principle of a spin-torque oscillator, of which the frequency is efficiently controlled by manipulating the magnetostrictive anisotropy. To justify the scheme, we simulate a conventional magnetic-tunnel junction-based oscillator which is fabricated on a piezoelectric material. By applying mechanical stress to a free layer using a piezoelectric material, the oscillation frequency can be controlled to ensure a broad tuning range without a significant reduction of the dynamic resistance variation. Such controllability, which appears in the absence of an external magnetic field, will not only enable the integration of spin-torque oscillators and conventional complimentary metal-oxide semiconductor technology but will also broaden the applicability of spin-torque oscillators.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Temporal Pattern Recognition with Delayed-Feedback Spin-Torque Nano-Oscillators

The recent demonstration of neuromorphic computing with spin-torque nano-oscillators has opened a path to energy efficient data processing. The success of this demonstration hinged on the intrinsic short-term memory of the oscillators. We extend the memory of the spin-torque nano-oscillators through time-delayed feedback. We leverage this extrinsic memory to increase the efficiency of solving pattern recognition tasks that require memory to discriminate different inputs. Here, the large tunability of these nonlinear oscillators allows us to control and optimize the delayed-feedback memory using different operating conditions of applied current and magnetic field.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Toward error-free scaled spin torque majority gates

The functionality of a cross-shaped Spin Torque Majority Gate is explored by means of micromagnetic simulations. The different input combinations are simulated varying material parameters, current density and size. The main failure mode is identified: above a critical size, a domain wall can be pinned at the center of the cross, preventing further propagation of the information. By simulating several phase diagrams, the key parameters are obtained and the operating condition is deduced. A simple relation between the domain wall width and the size of the Spin Torque Majority Gate determines the working range. Finally, a correlation is found between the energy landscape and the main failure mode. We demonstrate that a macrospin behavior ensures a reliable majority gate operation.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Increased magnetic damping of a single domain wall and adjacent magnetic domains detected by spin torque diode in a nanostripe

Spin torque resonance has been used to simultaneously probe the dynamics of a magnetic domain wall and of magnetic domains in a nanostripe magnetic tunnel junction. Due to the large associated resistance variations, we are able to analyze quantitatively the resonant properties of these single nanoscale magnetic objects. In particular, we find that the magnetic damping of both the domains and the domain wall is doubled compared to the damping value of the host magnetic layer. We estimate the contributions to the damping arising from the dipolar couplings between the different layers in the junction and from the intralayer spin pumping effect, and find that they cannot explain the large damping enhancement that we observe. We conclude that the measured increased damping is intrinsic to large amplitudes excitations of spatially localized modes or solitons such as vibrating or propagating domain walls.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Effect of stripe height on the critical current density of spin-torque noise in a tunneling magnetoresistive read head with a low resistance area product below 1.0 Ω μm{sup 2}

To understand the spin-torque effect on the noise in tunneling magnetoresistive (TMR) read heads, the GHz range noise spectra of TMR read heads with a narrow track width (w = 36 nm), and various stripe heights (h) are investigated as a function of the external magnetic field (H{sub ex}) and dc bias current density (j). The strong noise peak intensity depends on both H{sub ex} and j, indicating that the spin-torque affects the thermal mag-noise under a positive (negative) j for a positive (negative) H{sub ex}, regardless of h in the TMR heads. Due to the increased shape anisotropy, the critical current density (j{sub c}), where the non-thermal fluctuation noise originates from the spin-torque, increases markedly as the head dimension is reduced, and the maximum value of j{sub c} is approximately +1.5 × 10{sup 12} A/m{sup 2} for a head with w = 36 nm and h = 15 nm. These results demonstrate that the non-thermal fluctuation noise originating from the spin-torque in the TMR head can be suppressed in the current density range below 10{sup 12} A/m{sup 2}, as the head dimension is reduced and the shape anisotropy is increased.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Thermally activated switching of perpendicular magnet by spin-orbit spin torque

We theoretically investigate the threshold current for thermally activated switching of a perpendicular magnet by spin-orbit spin torque. Based on the Fokker-Planck equation, we obtain an analytic expression of the switching current, in agreement with numerical result. We find that thermal energy barrier exhibits a quasi-linear dependence on the current, resulting in an almost linear dependence of switching current on the log-scaled current pulse-width even below 10 ns. This is in stark contrast to standard spin torque switching, where thermal energy barrier has a quadratic dependence on the current and the switching current rapidly increases at short pulses. Our results will serve as a guideline to design and interpret switching experiments based on spin-orbit spin torque.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Temperature-dependent anisotropic magnetoresistance and spin-torque-driven vortex dynamics in a single microdisk

Spin-orbit-torque-driven dynamics have recently gained interest in the field of magnetism due to the reduced requirement of current densities and an increase in efficiency, as well as the ease of implementation of different devices and materials. From a practical point of view, the low-frequency dynamics below 1GHz is particularly interesting since dynamics associated with magnetic domains lie in this frequency range. While spin-torque excitation of high-frequency modes has been extensively studied, the intermediate low-frequency dynamics have received less attention, although spin torques could potentially be used for both manipulation of the spin texture and the excitation of dynamics. In this paper, we demonstrate that it is possible to drive magnetic vortex dynamics in a single microdisk by spin-Hall torque at varying temperatures and relate the results to transport properties. We find that the gyrotropic mode of the core couples to the low-frequency microwave signal and produces a measurable voltage. The dynamic measurements are in agreement with magnetic transport measurements and are supported by micromagnetic simulations. Our results open the door for integrating magnetic vortex devices in spintronic applications.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Mode coupling in spin torque oscillators

A number of recent experimental works have shown that the dynamics of a single spin torque oscillator can exhibit complex behavior that stems from interactions between two or more modes of the oscillator, such as observed mode-hopping or mode coexistence. There has been some initial work indicating how the theory for a single-mode (macro-spin) spin torque oscillator should be generalized to include several modes and the interactions between them. In the present work, we rigorously derive such a theory starting with the Landau–Lifshitz–Gilbert equation for magnetization dynamics by expanding up to third-order terms in deviation from equilibrium. Here, our results show how a linear mode coupling, which is necessary for observed mode-hopping to occur, arises through coupling to a magnon bath. In conclusion, the acquired temperature dependence of this coupling implies that the manifold of orbits and fixed points may shift with temperature.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Unidirectional response in spin-torque driven magnetization dynamics

It was recently demonstrated in bilayers of permalloy and platinum, that by combining spin torques arising from the spin Hall effect with Oersted field-like torques, magnetization dynamics can be induced with a directional preference.(1) This "unidirectional" magnetization dynamic effect is made possible by exploiting the different even and odd symmetry that damping-like and field-like torques respectively have when magnetization is reversed. The experimental method used to demonstrate this effect was the spin-torque ferromagnetic (ST-FMR) resonance technique; a popular tool used in the phenomenological quantification of a myriad of damping-like and field-like torques. In this report, we review the phenomenology which is used to describe and analyze the unidirectional magnetization dynamic effect in ST-FMR measurements. We will focus on how the asymmetry in the dynamics also is present in the phase angle of the magnetization precession. We conclude by demonstrating a utility of this directional effect; we will outline an improved experimental method that can be used to distinguish a phase-shifted field-like torque in a ST-FMR experiment from a combination of field-like and damping-like torques.

Sklenar, J.↗
DOE OSTI2020

Interfacial spin–orbit torques

Spin–orbit torques offer a promising mechanism for electrically controlling magnetization dynamics in nanoscale heterostructures. While spin–orbit torques occur predominately at interfaces, the physical mechanisms underlying these torques can originate in both the bulk layers and at interfaces. Classifying spin–orbit torques based on the region that they originate in provides clues as to how to optimize the effect. While most bulk spin–orbit torque contributions are well studied, many of the interfacial contributions allowed by symmetry have yet to be fully explored theoretically and experimentally. To facilitate progress, we review interfacial spin–orbit torques from a semiclassical viewpoint and relate these contributions to recent experimental results. In this study, we show the relationship between different interface transport parameters within the same model. For charges and spins flowing perpendicular to the interface, interfacial spin–orbit coupling both modifies the mixing conductance of the magnetoelectronic circuit theory and gives rise to spin memory loss. For in-plane electric fields, interfacial spin–orbit coupling gives rise to torques described by spin–orbit filtering, spin swapping, and precession. In addition, these same interfacial processes generate spin currents that flow into the non-magnetic layer. For in-plane electric fields in trilayer structures, the spin currents generated at the interface between one ferromagnetic layer and the non-magnetic spacer layer can propagate through the non-magnetic layer to produce novel torques on the other ferromagnetic layer.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Observation of thermally driven field-like spin torque in magnetic tunnel junctions

We report the thermally driven giant field-like spin-torque in magnetic tunnel junctions (MTJ) on application of heat current from top to bottom. The field-like term is detected by the shift of the magneto-resistance hysteresis loop applying temperature gradient. We observed that the field-like term depends on the magnetic symmetry of the MTJ. In asymmetric structures, with different ferromagnetic materials for free and fixed layers, the field-like term is greatly enhanced. Our results show that a pure spin current density of the order of 10{sup 9 }A/m{sup 2} can be produced by creating a 120 mK temperature difference across 0.9 nm thick MgO tunnelling barrier. Our results will be useful for writing MTJ and domain wall-based memories using thermally driven spin torque.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Local spin torque induced by electron electric dipole moment in the YbF molecule

In this study, we show the modification of the equation of motion of the electronic spin, which is derived by the quantum electron spin vorticity principle, by the effect of the electron electric dipole moment (EDM). To investigate the new contribution to spin torque by EDM, using first principle calculations, we visualize distributions of the local spin angular momentum density and local spin torque density of the YbF molecule on which the static electric field and magnetic field are applied at t = 0.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Optimization of spin-torque switching using AC and DC pulses

We explore spin-torque induced magnetic reversal in magnetic tunnel junctions using combined AC and DC spin-current pulses. We calculate the optimal pulse times and current strengths for both AC and DC pulses as well as the optimal AC signal frequency, needed to minimize the Joule heat lost during the switching process. The results of this optimization are compared against numeric simulations. Finally, we show how this optimization leads to different dynamic regimes, where switching is optimized by either a purely AC or DC spin-current, or a combination AC/DC spin-current, depending on the anisotropy energies and the spin-current polarization.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Modulation bandwidth of spin torque oscillators under current modulation

For practical applications of spin torque nano-oscillators (STNO), one of the most critical characteristics is the speed at which an STNO responds to variations of external control parameters, such as current or/and field. Theory predicts that this speed is limited by the amplitude relaxation rate Γ{sub p} that determines the timescale over which the amplitude fluctuations are damped out. In this study, this limit is verified experimentally by analyzing the amplitude and frequency noise spectra of the output voltage signal when modulating an STNO by a microwave current. In particular, it is shown that due to the non-isochronous nature of the STNO the amplitude relaxation rate Γ{sub p} determines not only the bandwidth of an amplitude modulation, but also the bandwidth of a frequency modulation. The presented experimental technique will be important for the optimisation of the STNO characteristics for applications in telecommunications or/and data storage and is applicable even in the case when the STNO output signal is only several times higher than noise.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Spin-torque switching of a nano-magnet using giant spin hall effect

The Giant Spin Hall Effect(GSHE) in metals with high spin-orbit coupling is an efficient way to convert charge currents to spin currents, making it well-suited for writing information into magnets in non-volatile magnetic memory as well as spin-logic devices. We demonstrate the switching of an in-plane CoFeB magnet using a combination of GSHE and an external magnetic field. The magnetic field dependence of the critical current is used to estimate the spin hall angle with the help of a thermal activation model for spin-transfer torque switching of a nanomagnet.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Critical current and linewidth reduction in spin-torque nano-oscillators by delayed self-injection

Based on theoretical models, the dynamics of spin-torque nano-oscillators can be substantially modified by re-injecting the emitted signal to the input of the oscillator after some delay. Numerical simulations for vortex magnetic tunnel junctions show that with reasonable parameters this approach can decrease critical currents as much as 25% and linewidths by a factor of 4. Analytical calculations, which agree well with simulations, demonstrate that these results can be generalized to any kind of spin-torque oscillator.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗