Dynamically stabilized magnetic skyrmions

Dr Zhou, Yan   (Principal Investigator (PI))

Professor Akerman Johan   (Co-Investigator)

Professor Cui Xiaodong   (Co-Investigator)

4

2015-08-01

2015-11-30

43000

Dynamically stabilized magnetic skyrmions

droplet soliton, magnetic, magnetic nanostructure, skyrmion topological, spin torque oscillators, spin transfer torque

Physics,Others - Electrical and Electronic Engineering

Physical Sciences (P)

201507159006

Seed Fund for PI Research – Basic Research

2015

Completed

Objectives: • To develop an analytical theory of dynamical magnetic skyrmions (DMS) in nano-contact spin torque oscillator (NC-STO) with a perpendicular magnetic anisotropy (PMA) free layer by including the new ingredient of interfacial Dzyaloshinskii–Moriya interaction (DMI). • To develop the micromagnetics framework for describing the rich dynamics of DMS using the Landau–Lifshitz–Gilbert equations with a particular focus on new ingredients of PMA and DMI. • To develop a fully integrated simulation environment combining spin torque, spin Hall effect, electron and spin transport, heat generation/transport, microwave signal generation, all on a Graphic Processing Unit (GPU) accelerated platform. Key issues: 1) Whether a magnetic skyrmion can be stabilized without DMI is a cutting-edge and controversial issue in condensed matter physics. 2) There are intensive debate on the theoretical grounding of existence and maintenance of magnetic skyrmion in magnetic nanostructures. 3) The physical mechanism of transition between quasiparticles with different topological numbers are not clear. Problems to be tackled: This project aims to investigate, numerically, theoretically, and experimentally, an entirely novel, unexpected, and intriguing dynamic magnetic object — the dynamical magnetic skyrmion (DMS), that combines the properties of droplets and skyrmions. The success of this project will open up new possibilities and concepts in magnetic logic and information processing devices with low-power, enhanced performance, low-cost mass data storage, therefore bringing profound technological impacts. We will mainly focus on the following two problems. 1) We have very recently proposed and demonstrated numerically a novel dynamic and topological magnetic soliton — the DMS, that combines the properties of droplets and skyrmions [15]. To better analyze this novel magnetodynamic nano-object we will develop an analytical theory of DMS by including the new ingredient of interfacial DMI. We will explore the consequences of the fundamental DMS property of topological protection as well as what consequences its dynamic character will have on the topological Hall effect (THE) and the Berry phase [28]. As compared to the prevailing theory where skyrmions are treated as particles [29], our string theory will be capable of studying various internal modes of DMS by taking into account the internal degrees of freedom. The theory will bring a closure to the long lingering issue of precondition of skyrmion existence and stabilization. It will also determine the criteria of transformation between topological and nontopological quasiparticles in magnetic nanostructures. 2) We will extend the micromagnetic simulations by inclusion of DMI to study the detailed dynamical properties of the DMS as a function of current density and applied magnetic field, and to compare its dynamical properties with the properties of the droplet. The comprehensive understanding of all the important dynamical and topological aspects of this novel dynamic nanomagnetic object will be particularly valuable for the further experimental and applied studies of using the DMS for microwave generation and memory applications. The transformation between non-topological and topological quasiparticles may bring about a theoretical breakthrough and will certainly generate significant interest in both the fundamental and applied communities.