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.
We apply a non-abelian gauge field approach to generalize the micromagnetic energy description of a ferromagnet. This approach, without further assumption, takes into account three different energy terms: the well-known exchange term, chiral ones, and an intrinsic anisotropy term. In the non-abelian gauge field approach, the covariant gauge derivative plays a key role. The result is the emergence of a Dzyaloshinskii-Moriya-like energy term under two conditions: the first one is the pure gauge field background and the second one is the presence of a static electric field. Moreover, this approach allows one to reach a more deep understanding of the micromagnetics theory if rewritten in a gauge-invariant formulation. In this article, clearly emerges the interpretation of the voltage-controlled magnetic anisotropy (VCMA) mechanism.
Magnetization dynamics in uniformly magnetized nanomagnets excited by time-harmonic (AC)\ud
external fields or spin-polarized injected currents is considered. The analysis is focused on the\ud
behaviour of the AC-excited dynamics near saddle equilibria. It turns out that this dynamics has a\ud
chaotic character at moderately low power level. This chaotic and fractal nature is due to the phenomenon\ud
of heteroclinic tangle which is produced by the combined effect of AC-excitations and\ud
saddle type dynamics. By using the perturbation technique based on Melnikov function, analytical\ud
formulas for the threshold AC excitation amplitudes necessary to create the heteroclinic tangle are\ud
derived. Both the cases of AC applied fields and AC spin-polarized injected currents are treated.\ud
Then, by means of numerical simulations, we show how heteroclinic tangle is accompanied by the\ud
erosion of the safe basin around the stable regimes
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