Spin Transfer Torques in Cobalt / Platinum Based Chiral Magnets
Grab, Jennifer L
Skyrmions are topologically protected quasiparticles in the form of stable spin textures in a magnetic material. Because skyrmions can be smaller than the domain size in a ferromagnet, they are promising candidates for high density information storage. Finding an efficient way to create and annihilate individual skyrmions under ambient conditions is an important first step toward realizing skyrmion-based technologies. In this dissertation, I will discuss two experiments where we attempt to create a static or dynamic skyrmion in cobalt / platinum bilayers using a spin valve like device geometry. I will also cover in detail the growth and characterization of the perpendicularly magnetized Co/Pt films necessary for this work. The first project involves a hard Co/Pt bilayer with a strong Dzyaloshinskii Moriya Interaction, in addition to strong perpendicular anisotropy. Micromagnetic simulations have predicted that it should be possible to excite skyrmion dynamics in such systems using a spin polarized current. Although our experimental results are inconclusive, we have developed a fabrication process and measurement techniques that will be useful for future investigation of dynamics in similar materials. The second project is related, but instead uses very soft Co/Pt bilayers, which show chiral stripe domains at zero field. We are able to separate out the behavior of the film beneath the nanopillar from the bulk film and show that the two switch independently of each other. This indicates that there is some sort of domain, potentially a skyrmion, that we are able to control separately from the rest of the film. This project is a good first step toward controlling and creating room temperature skyrmions using spin transfer torque.
Applied physics; Spintronics; Materials Science; Condensed matter physics; chiral magnets; magnetic materials; skyrmions; spin transfer torque; Nanoscience
Ralph, Daniel C.
Parpia, Jeevak M.; Kim, Eun-Ah
Ph. D., Physics
Doctor of Philosophy
dissertation or thesis