Defense PhD Thesis

MSc. Sergei Krylov

IEE SAS, June 18, 2024,  1,00 p.m.

Title: Magnetic structures at nanoscale

Abstract:
This thesis focuses on advancements in the domain of magnetic nanostructures, with a dual focus on enhancing the capabilities of magnetic force microscopy (MFM) and optimizing focused ion beam (FIB) technologies. The work aims to address the critical needs of nanoscale magnetic research, spanning applications from data storage to spintronics. This work introduces methodologies to refine the precision and efficacy of these basic analytical tools.
In the first segment of the thesis, we concentrate on MFM, a technique celebrated for its non-destructive imaging capabilities that allow for the direct visualization of magnetic domain structures without necessitating complicated sample preparation. Despite its advantages, conventional MFM has been qualitative. This research advances MFM by adopting and refining a technique initially proposed by our colleagues. It uses a disk from a soft magnetic material featuring a vortex core (VC) in its center to enhance imaging resolution. In the thesis, we address the challenge of VC stability, a significant advancement is achieved by introducing geometric modifications to the disk—namely, a central cavity designed to pin the VC in place. This stabilization directly translates to improved resolution and capabilities in MFM imaging. This advancement is a step towards achieving quantitative MFM.
Another innovation is explored by combining a small cylindric probe with a disk underneath it. The VC within such a disk provides stabilization, offering new avenues for enhancing MFM technology. While experimental validation of such an approach is set as a future objective, the theoretical and initial experimental results we presented suggest a promising direction for achieving high-resolution magnetic imaging.
The second focus of the thesis optimizes FIB technology for precise material structuring at minimized ion dosages, which is essential for preserving the magnetic integrity of materials. By developing a novel algorithm and employing multilayer structures of permalloy-titanium-silicon, this work addresses and overcomes challenges associated with local heating and silicon atom displacement into permalloy layer during FIB processing. These improvements not only enhance the precision of FIB cuts but also ensure the preservation of the material’s magnetic properties. These improvements also facilitate the creation of intricate magnetic structures suitable for advanced applications in magnonics and spintronics.
This thesis contributes to the field of nanoscale magnetic research by providing innovative improvements to MFM and FIB methodologies. The findings and advancements reported herein hold the potential to enhance the development of future magnetic technologies, pushing the boundaries of what is currently achievable in nanoscale magnetic research.