Fractional Topology in Hybrid Magnetic Skyrmions

Parker, William S

Magnetic materials were first used to record information over a century ago when Valdemar Poulsen used a magnetic wire recorder to record and play back audio in 1900. From that first device to the magnetic hard drives ubiquitous in big data centers today, there have been seemingly endless schemes for how to use magnetism to store and manipulate information. In that time, semiconductor information storage has gained dominance in consumer devices, but the relatively low cost and long lifespan of hard drives makes them the preferred choice in big data and commercial applications. However, hard drives have their own drawbacks, most notably their energy consumption - a 2016 study estimated that in 2014, U.S. data centers consumed 1.8% of total U.S. power consumption. A more recent study from the Electric Power Research Institute puts that figure at 4% of total U.S. power consumption in 2023, with generative artificial intelligence models pushing that number higher in years to come. The need for low-cost, low-energy, long-lifespan non-volatile computer memory is high and increasing. With this need comes a new candidate information carrier, the magnetic skyrmion. Magnetic skyrmions are topologically protected particle-like magnetic configurations that can be driven through a material at low current densities, making them promising for use in magnetic logic and memory devices. However, their integration into real world devices requires a better understanding of their structure and behavior, and the measurement techniques to achieve that. In this work, I lay out a theoretical framework to capture the novel topology of skyrmions in one of the most promising host systems, Fe/Gd multilayer thin films, and show how it explains their stability. I then describe novel magnetic imaging techniques, and apply them to this host system to gain a full understanding of the skyrmions within it.

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