Dynamics and morphology of chiral magnetic bubbles in perpendicularly magnetized ultra-thin films

TL;DR

This study investigates the complex dynamics and shape features of magnetic bubbles in ultra-thin films with disorder and Dzyaloshinskii-Moriya interaction, revealing ripple-like shapes and variable interaction fields through simulations and modeling.

Contribution

It introduces an extended collective coordinate model for magnetic bubbles and uncovers the origin of ripple-like shapes and variable Dzyaloshinskii-Moriya fields in simulations.

Findings

Ripple-like bubble shapes cause kink features in velocity curves.

Vertical Bloch lines nucleate and interact, affecting bubble morphology.

Dzyaloshinskii-Moriya interaction field varies with in-plane field.

Abstract

We study bubble domain wall dynamics using micromagnetic simulations in perpendicularly magnetized ultra-thin films with disorder and Dzyaloshinskii-Moriya interaction. Disorder is incorporated into the material as grains with randomly distributed sizes and varying exchange constant at the edges. As expected, magnetic bubbles expand asymmetrically along the axis of the in-plane field under the simultaneous application of out-of-plane and in-plane fields. Remarkably, the shape of the bubble has a ripple-like part which causes a kink-like (steep decrease) feature in the velocity versus in-plane field curve. We show that these ripples originate due to the nucleation and interaction of vertical Bloch lines. Furthermore, we show that the Dzyaloshinskii-Moriya interaction field is not constant but rather depends on the in-plane field. We also extend the collective coordinate model for domain wall motion to a magnetic bubble and compare it with the results of micromagnetic simulations.