Experimental Evaluation of the Interfacial Dzyaloshinskii-Moriya Interaction in Co/Ni Magnetic Multilayers

2018-10-22T20:59:45Z (GMT) by Derek Lau
In this thesis work, different approaches to engineer spin-orbit coupling phenomena has been explored experimentally because of their importance in next generation spintronic devices. The studies are focused primarily on tuning the Dzyaloshinskii-Moriya Interaction for more efficient current-induced domain wall motion in thin films composed of Co/Ni repeating magnetic layers.<br> The Dzyaloshinskii-Moriya Interaction (DMI) is initially characterized for the Pt/[Co/Ni]_2.5/Ta system to develop a suitable experimental methodology for future material systems. We performed preliminary studies on the system in order to obtain the necessary texture, perpendicular anisotropy, coercivity, and film morphology. In order to characterize the interfacial DMI, we measure field-driven, asymmetric domain wall growth through the use of a Magneto-Optical Kerr Effect Microscope (MOKE). Using this technique, we are able to determine the effective field (H_DMI) generated by the interfacial DMI. This experimental characterization was significant in the development of a comprehensive model for describing domain wall behavior, used to guide the analysis of subsequent studies. Despite the ubiquitous role of alloying in developing magnetic materials, there have been few studies of its impact on DMI in heavy metal seedlayers. We used combinatorial techniques to examine a range of heavy metal alloy seedlayers. A [Co/Ni]_2.5/Ta multilayer is deposited on top of a seedlayer solid solution with a composition gradient. We have characterized the Pt−Ir system to find that the DMI changes magnitude as one moves across the composition range. A similar trend has been characterized in the Pt−Au alloyed seedlayer systems. We have demonstrated that other factors (namely chiral damping effects) not related to DMI may be contributing to domain wall motion. In addition, we have also been able to characterize the effect of seedlayer alloying on the efficiency of current-induced domain wall motion (CIDWM), which is ultimately the metric that matters for future domain wall devices. We show a correlation between DMI and device performance to demonstrate the viability of tuning device performance through seedlayer composition. Finally, we discuss preliminary results for a study to characterize the effects of capping layer interfaces on the effective DMI induced in a magnetic multilayer. There are relative magnitude differences between different heavy metal/ferromagnet (and vice versa) inter-faces, which have implications for tuning DMI by designing the magnetic multilayer structure. Continuing this study through computational and experimental work shows potential for engineering of DMI in superlattice structures or magnetic multilayers for spintronics applications.<br>