Observation of magnetic droplets in magnetic tunnel junctions

Abstract

Magnetic droplets, a class of highly nonlinear magnetodynamic solitons, can be nucleated and stabilized in nanocontact spin-torque nano-oscillators. Here we experimentally demonstrate magnetic droplets in magnetic tunnel junctions (MTJs). The droplet nucleation is accompanied by power enhancement compared with its ferromagnetic resonance modes. The nucleation and stabilization of droplets are ascribed to the double-CoFeB free-layer structure in the all-perpendicular MTJ, which provides a low Zhang-Li torque and a high pinning field. Our results enable better electrical sensitivity in fundamental studies of droplets and show that the droplets can be utilized in MTJ-based applications and materials science.

Domain wall magnetic tunnel junction-based artificial synapses and neurons for all-spin neuromorphic hardware

“…Figures 4 c and 4d refer to R-H loops of the MTJ device before and after PCs etch process, respectively. The measured low TMR ~ 14% (much small than that of pristine DW-pMTJ device ~145%) is attributed to the larger device size and the two-probe magneto-resistance measurement, which can be improved by device scaling and measurement optimization in the future 66 . Transport measurements were carried out upon the application of a large saturating magnetic field (3 kOe) along the - z direction.…”

Spin torque oscillator based on magnetic tunnel junction with MgO cap layer for radio-frequency-oriented neuromorphic computing

“…Many inspiring works have been reported, including multilevel synapses based on spin torque memristors, neuromorphic computing based on the synchronization of spin oscillators, artificial neurons of ANNs based on spin torque stochastic switching and microwave detection, and spiking neurons with superparamagnetic tunnel junctions, etc. [15][16][17][18][19] More recently, it has been proposed numerically and proved experimentally that MTJ-based spin torque diodes (STDs) can act as spintronic synapses and carry out radio-frequency (RF) multiply-and-accumulate (MAC) operation by rectifying the input microwave power into direct voltages. [20,21] Correspondingly, spin torque oscillators (STOs) can be used as artificial neurons and perform nonlinear activation through converting the direct current into microwave power.…”

Field-Free High-Frequency Exchange-Spring Spin-Torque Nano-Oscillators

“…Magnetic anisotropies of those ferromagnetic layers are key in determining the operation performances in STNOs. For instance, in STNOs with in-plane magnetic anisotropic (IMA) ferromagnetic layers, the microwave line width and power can be improved dramatically by synchronizing the propagating spin waves. , Nevertheless, a high magnetic field is generally required in these in-plane STNOs to produce a noncollinear magnetic configuration, for the sake of maximizing the current-induced spin torques and detecting the auto-oscillating signals. , Using materials with perpendicular magnetic anisotropy (PMA) as the free layer and/or the reference layer − may be a solution to this issue, where novel dynamic mode (magnetic droplet) can even be generated at a low field regime. , Specifically, STNOs with two IMA free layers and two PMA reference layers were studied theoretically, showing larger precession amplitude and high-frequency field-free operation, promising for developing high-power high-frequency STNOs …”

“…It is noteworthy, that the slope of the resistance vs field has now changed sign compared to the t-AP state, consistent with the reversed magnetization of the droplet. In contrast to the droplet forming in the high-field P state (Figure 2a), where the all-perpendicular symmetry of the state cancels out the droplet microwave signal, 10,34,35 here, the microwave signal from the droplet is directly observed, again confirming the low-field tilted state of the Co layer with an in-plane component of its magnetization. 11,59 Finally, the droplet again comes with lowfrequency microwave noise, as it moves around in the NC region.…”