UCI Physicists Harness Chaos

Wed, 02/20/2019

(a) Two stable states of magnetization (pointing left or right) can be visualized as two potential wells separated by an energy barrier. Low dimensional chaos leads to an erosion of the barrier between the two potential wells and results in an increased switching rate. (b) The erosion of the stable regions within the well is fractal at zero temperature. (c) At room temperature, the fractal nature is smoothed out, but the erosion of the barrier remains.

Picture Credit: 
Krivorotov Group
UCI Physical Sciences

A research team including University of California, Irvine scientists Ilya Krivorotov, Eric Montoya, and Yu-Jin Chen and researchers from the University of Naples (Federico II and “Parthenope”) have demonstrated that chaos can be exploited to drive magnetization switching in nanoscale ferromagnets. This discovery, featured as one of the Editors’ Highlights published in Nature Communications, shows that low dimensional magnetic chaos induced by alternating spin torque can strongly increase the rate of thermally-activated magnetic switching in a nanoscale ferromagnet.

 

In the 1880s, Henri Poincaré discovered the remarkable complexity that may appear in the trajectories of a nonlinear deterministic dynamical system while studying the three-body problem of celestial mechanics. This pioneering work revealed strong sensitivity of the dynamic trajectories to small perturbations and gave birth to a branch of science that studies chaos—deterministic dynamics extremely sensitive to initial conditions. This new work studies chaos on a much smaller length scale and is one of the first clear attempts to detect low dimensional chaos in nanoscale systems at room temperature.

 

The intriguing interplay discovered between low-dimensional deterministic chaos and temperature-induced stochastic dynamics is not only of fundamental interest but also of substantial practical importance. This is because energy-efficient switching of magnetization is a crucial problem in nonvolatile magnetic storage and magnetic neuromorphic computing. In fact, energy-efficient and non-volatile magnetic storage technologies such as spin transfer torque memory (STT-RAM) and microwave-assisted magnetic recording (MAMR) rely on thermally assisted switching of nanoscale ferromagnets. This discovery reveals that chaos can be employed for reduction of the effective magnetic energy barrier for switching of magnetization in a nanoscale ferromagnet and thereby paves the way towards more energy-efficient nonvolatile magnetic storage and logic technologies.

 

This work was funded by the National Science Foundation, the Army Research Office, and Defense Threat Reduction Agency.