Magnetic domain walls as broadband spin wave and elastic magnetisation wave emitters

Rasmus B Holländer,Martina Gerken,Cai Müller,Julius Schmalz,Jeffrey Mccord

doi:10.1038/s41598-018-31689-8

Rasmus B Holländer, Martina Gerken + Show 3 more

Open Access

https://doi.org/10.1038/s41598-018-31689-8

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Journal: Scientific Reports	Publication Date: Sep 17, 2018
Citations: 24	License type: open-access

Affiliation: Kiel University, Fachhochschule Kiel

Abstract

We report on the direct observation of spin wave and elastic wave emission from magnetic domain walls in ferromagnetic thin films. Driven by alternating homogeneous magnetic fields the magnetic domain walls act as coherent magnetisation wave sources. Directional and low damped elastic waves below and above the ferromagnetic resonance are excited. The wave vector of the magnetoelastically induced acoustic waves is tuned by varying the excitation frequency. The occurrence of elastic wave emission is proved by a combination of micromagnetic and mechanical finite element simulations. Domain wall emitted magnetostatic surface spin waves occur at higher frequencies, which characteristics are confirmed by micromagnetic simulations. The distinct modes of magnetisation wave excitation from micromagnetic objects are a general physical phenomenon relevant for dynamic magnetisation processes in structured magnetic films. Magnetic domain walls can act as reconfigurable antennas for spin wave and elastic wave generation. The wave orientation can be controlled separately via the domain wall orientation for elastic waves and via magnetization orientation for magnetostatic surface spin waves.

Highlights

Relying on local excitation, spin waves offer the possibility to substitute modern day electronics by wave-computing[1,2,3]
In25 it was shown that elastic waves induce precessional motion of magnetisation in a magnetostrictive thin film deposited on a piezoelectric substrate through strain mediation
We focus on the magnetisation waves emitted by the central domain walls. These correspond to coherent elastic wave superpositions resulting from wave emission from the dynamically excited domain walls

Summary

Introduction

Spin waves offer the possibility to substitute modern day electronics by wave-computing[1,2,3]. Numerical studies suggest the utilisation of domain walls as directional spin wave emitters[14,15]. An evidence of such a behaviour was shown only once[16]. The elastic magnetisation wave[21] excitation from local piezoelectric antennas due to excitation of alternating strain induced anisotropy in magnetostrictive ferromagnetic layers was shown experimentally[22]. We prove the antenna free emission of magnetostatic spin waves and, in particular, elastic magnetisation waves in ferromagnetic films from asymmetric Bloch and Néel type domain walls[26] by direct time-resolved magneto-optical imaging in conjunction with complementary simulations. We show that domain walls offer an alternative and flexible excitation scheme for elastic magnetisation waves and spin waves

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