Sub-nanosecond signal propagation in anisotropy-engineered nanomagnetic logic chains

Zheng Gu,Mohmmad T Alam,Matthew A Marcus,Mark E Nowakowski,Ralph Storz,Peter Fischer,Patrick Bennett,Andrew Doran,Brian Lambson,Anthony Young,Jeffrey Bokor,Andreas Scholl,Weilun Chao,David B Carlton,Mi-Young Im,Jeongmin Hong

doi:10.1038/ncomms7466

Abstract

Energy efficient nanomagnetic logic (NML) computing architectures propagate binary information by relying on dipolar field coupling to reorient closely spaced nanoscale magnets. Signal propagation in nanomagnet chains has been previously characterized by static magnetic imaging experiments; however, the mechanisms that determine the final state and their reproducibility over millions of cycles in high-speed operation have yet to be experimentally investigated. Here we present a study of NML operation in a high-speed regime. We perform direct imaging of digital signal propagation in permalloy nanomagnet chains with varying degrees of shape-engineered biaxial anisotropy using full-field magnetic X-ray transmission microscopy and time-resolved photoemission electron microscopy after applying nanosecond magnetic field pulses. An intrinsic switching time of 100 ps per magnet is observed. These experiments, and accompanying macrospin and micromagnetic simulations, reveal the underlying physics of NML architectures repetitively operated on nanosecond timescales and identify relevant engineering parameters to optimize performance and reliability.

Highlights

Energy efficient nanomagnetic logic (NML) computing architectures propagate binary information by relying on dipolar field coupling to reorient closely spaced nanoscale magnets
When islands are arranged in a line parallel to the minor axis, the nearest-neighbour magnetic dipolar field coupling imparts a preference for the magnetization of these neighbouring islands to align antiparallel, forming a spatial logical inverter[5]
To obtain a better physical understanding of the experimental data, we investigate both an adiabatic analytic model based on first-principles equations at 0 K (Supplementary Note 5) in addition to macrospin simulations that vary the temperature, nanomagnet size, anisotropy energy and dipolar coupling strength to identify parameter space requirements for perfect signal propagation

Summary

Introduction

Energy efficient nanomagnetic logic (NML) computing architectures propagate binary information by relying on dipolar field coupling to reorient closely spaced nanoscale magnets. Successive logic operations, the entire NML architecture (chains and majority logic gates) must be reinitialized after each operation This resetting process is known as clocking, and in this work we use pulsed nanosecond on-chip magnetic fields[8] to drive the magnetization of all nanomagnets in a chain to saturation along their magnetic hard axes. The time-dependent relaxation from the null state in rectangular or elliptically shaped magnets, can be affected by factors such as thermal fluctuations[9,10,11,12,13] and non-ideal magnetic anisotropies[14] These aberrations can drive the magnetization of individual islands to spontaneously switch out of sequence, forming an error that spoils the sequentially directed dipolar coupling, which correctly propagates the input information. Even though reliable high-speed operation has been predicted[11,12,13], it has yet to be experimentally studied in any NML architecture

Methods

Results

Conclusion