Imaging Nanoscale Spin Textures with Scanning Diamond Quantum Microscopy

Abstract

Magnetic materials play a key role in the advancement of modern technology, from data storage mediums and giant magnetoresistance read heads for information processing, to medical applications like drug delivery and magnetic resonance imaging. Their research and development have progressed towards ever-reducing spatial and magnetic footprints, largely motivated by promising novel properties emerging at reduced dimensions and the miniaturization of technology. Sustained research progress will therefore require the timely development of scalable probing techniques with enhanced sensitivities. State-of-the-art material research requirements of non-perturbative measurements, with resolutions of at least a hundred nanometers, and sensitivities down to single magnetic atomic layers, are becoming increasingly inaccessible by conventional spatial imaging techniques. In this respect, quantum sensing via nitrogen-vacancy centres in diamond promises to address contemporary and prospective imaging needs. Employed on a scanning probe platform, the scanning diamond quantum microscope is capable of nanoscale imaging with an unprecedented magnetic sensitivity down to the nano-Tesla regime and minimal magnetic back-action on the target. Scanning diamond quantum microscopy has been recently used to image a number of novel magnetic systems, however a large subset of materials, including various antiferromagnets and two-dimensional magnets, remains unexplored. Moreover, the technique is capable of secondary sensing modalities that are relatively underdeveloped and require systematic studies to understand their potentials and limitations. This thesis describes the work I have undertaken towards implementing a scanning diamond quantum microscope operational in cryogenic and ambient environments. I utilise this setup to develop imaging capabilities to study nanoscale non-trivial spin textures in topological (anti)ferromagnetic materials. The capabilities developed and physical insights revealed in this work establish the diamond quantum microscope as a powerful investigative tool for accelerating functional materials research towards future technologies.