Understanding the interaction of electron spins with magnetic materials is important from the standpoints of both fundamental physics and emerging technology. For example, spin-polarized currents can alter and induce magnetization dynamics through the spin-torque-transfer effect, enabling devices such as spin-torque-switched magnetic RAM and spin-transfer microwave oscillators. At the same time, spin-pumping effects--the production of spin currents from oscillating magnetization--are significantly altering our understanding of magnetization dynamics, particularly in nanoscale and confined geometries.
In this project, we explore the dynamics of individual spin transfer oscillators, and arrays of these oscillators coupled through various means: spin waves, electrical coupling, magnetic fields, and spin currents. These oscillator arrays are being researched for use as potential non-Boolean circuit elements to augment or replace CMOS architectures, and also as potential nanoscale, microwave-frequency tunable oscillators. Since each oscillator is a nonlinear element with distinct nonlinearities for each coupling mechanism, different array dynamics will emerge depending on the coupling. By controlling the coupling, the relative phases and frequencies of the oscillators in an array can be used as a metric for “degree of match” for a pattern matching algorithm, potentially having orders of magnitude improvements in speed, accuracy, and power consumption. For such architectures to be viable, we need to (1) understand the physics of individual oscillators (which depends on the nanoscale magnetic environment and the ferromagnet’s interaction with spin current) to improve individual oscillator function; (2) understand and quantify the coupling mechanisms between oscillators and how different couplings affect the nonlinear dynamics of arrays, with the goal of exploiting the physics to produce useful array behaviors; and (3) explore new oscillator architectures that use pure spin currents to drive dynamics to minimize the movement of charge through the devices, opening the possibility of nanoscale microwave oscillators with vastly improved power consumption. This research involves nanoscale fabrication and high speed measurement of devices and arrays, and potentially detailed simulations of individual device dynamics and the nonlinear dynamics of large arrays of oscillators coupled by various means./p>
Rippard WH, Deac AM, Pufall MR, et al: Physical Review B 81: 1, 2010
Pufall MR, Rippard WH, et al: Physical Review B 86: 094404, 2012
Spin electronics; NonBoolean logic; Ferromagnetic resonance; Spin transfer torque; Frequency entrainment; Nonlinear dynamics; Spin waves;