# Magnetic Force Microscopy with High Resolution and High Sensitivity: Quantitative Approach and Applications to Thin Film Multilayer Systems Supporting Skyrmions

Feng, Yaoxuan. Magnetic Force Microscopy with High Resolution and High Sensitivity: Quantitative Approach and Applications to Thin Film Multilayer Systems Supporting Skyrmions. 2022, Doctoral Thesis, University of Basel, Faculty of Science.

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Official URL: https://edoc.unibas.ch/90084/

In this dissertation, the high-resolution (HR-) MFM instrument used for the measurements in this dissertation shall be briefly introduced in Chapter 1, and the potential of improving its sensitivity is explored from the aspect of the probes that are being used. More precisely, the influence of (magnetic) coating on the MFM cantilevers is investigated and discussed in Chapter 3. Then, the MFM sensitivity is explained in detail in Chapter 4, making emphasis on the high-quality data that one can obtain with an advanced MFM instrument and improved probes, which are consistently employed for the MFM data acquisition in this dissertation. The quantitative approach for extracting sample magnetization from raw MFM data via the transfer function method is explained thoroughly in Chapter 5; the subtleties of data handling and the limitations of the method are also addressed. Ultimately, with the HR-MFM instrument and the improved cantilever tips, various magnetic thin film multilayer systems which support skyrmions are investigated. In Chapter 6, a ferro-/ferri-/ferromagnetic trilayer system which hosts two distinct skyrmion states is studied; by varying the Fe-sublayer thickness in the ferromagnetic layer, we show that the coexistence of the two skyrmion states can be continuously tuned. In Chapter 7, a hybrid ferro-/ferrimagnetic multilayer system and an antiferromagnetically-coupled skyrmion system are studied. In the first system, by substituting the Co-sublayer with Co-rich ferrimagnetic material, dense, close-to $M=0$ skyrmions can be obtained. In the second system, by combining the well-studied skyrmion layers with a bias layer, room-temperature zero-field skyrmions could be achieved. The newly observed skyrmion states in the two latter chapters will potentially offer solutions to some of the problems that still remain for implementing magnetic skyrmions for technical applications.