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, while 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 arrays of spin transfer oscillators coupled through various means: spin waves, electrical coupling, magnetic fields, and eventually spin currents. These oscillator arrays are being researched for use as potential NonBoolean 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 its interaction with spin current, to improve individual oscillator function; (2) quantify and understand the coupling mechanisms between oscillators and the nonlinear dynamics of arrays, with the goal of exploiting the physics to produce different array behaviors; and (3) explore new oscillator architectures that minimize the movement of charge through the use of pure spin currents to drive dynamics, opening the possibility of nanoscale microwave oscillators with vastly improved power consumption.
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;