UC San Diego

In this dissertation, we investigate the stabilization and dynamics of chiral domain walls and skyrmions in several ferromagnet/heavy metal thin-film multilayers. In each material system, the ferromagnet/heavy metal interfaces were engineered to give rise to an interfacial Dzyaloshinskii-Moriya interaction (iDMI) – a spin-orbit coupling mediated effect known to promote the formation of chiral magnetic textures. Throughout several comprehensive studies (presented herein as separate chapters), we explore the stabilization and dynamics of skyrmions in three distinct types of material systems: Thin-films close to experiencing a spin-reorientation transition, ultrathin films with low ferromagnetic exchange and high perpendicular magnetic anisotropy, and thick multilayers with large perpendicular magnetic anisotropy. Through experimental and theoretical studies, we explore the processes by which skyrmions can be created and moved in response to both quasi-static and transient electrical currents, magnetic fields, and temperature changes. In all cases, the systematic variation of material properties and experimental conditions to better understand and control the mechanisms by which skyrmions are stabilized is a key underlying theme.

In another thrust, we have studied the field-driven dynamics of chiral domain walls and have characterized a new effect in which magnetic stripe domains with chiral domain walls unidirectionally expand in response to applied magnetic fields, with growth symmetries that cannot be understood from the static energy frameworks typically employed to understand the impact of the interfacial Dzyaloshinskii-Moriya interaction in thin-film systems. Using analytical models, we have found that the in-plane torques generated by perpendicular magnetic fields stabilize steady-state domain wall magnetization profiles that are highly asymmetric in elastic energy, resulting in abnormal growth behaviors that are in line with the experimental findings. Building on this understanding of the field-driven dynamics of stripe domains, we expand this understanding to the growth directionalities observed when stripe domain motion is induced by spin-orbit torque.