In modern-day research, magnetometry provides valuable information for a wide range of studies. Among all the different forms of magnetometers, the nitrogenvacancy (NV) lattice defect in diamond has emerged as a powerful magnetic field sensor thanks to the combination of sensitivity, spatial resolution and versatile capabilities. High-fidelity microwave control and optical readout of the NV spin over a wide range of conditions has enabled applications in condensed matter physics, chemistry, biology, geoscience and many more. In particular, its capability of visualizing magnetic phenomena with high spatial resolution has proven to be a powerful tool in both fundamental physics and applied sciences. Advances in NV magnetometry in the past decade have led to numerous breakthroughs, especially in revealing the nanoscale physics of condensed matter systems. However, the free-space optics generally used for optical interrogation of the NV spins are challenging to realize in cryogenic, intra-cellular, or other hard-to-reach environments. As such, realizing robust all-fiber-based NV probes with efficient optical readout could enable new measurements in low-temperature (quantum) or biological systems...

Superconductors expel magnetic fields, a phenomenon known as the Meissner effect. This effect makes it notoriously difficult to predict the magnetic field around a superconductor. One successful way of calculating these fields is through conformal mappings; coordinate transformations that preserve Maxwell's equations of magnetic fields in free space. These were first described by Norris and later improved by Brandt. In this bachelor thesis, conformal mappings are introduced and applied to 8 situations of magnetic field screening of an increasingly complex nature. We look at the screening of applied magnetic fields and of magnetic fields due to a bias current running through a wire itself. We later compare these results with experimental observations of the Van der Sar lab in Delft and measurements from other papers.

Spin-waves, the propagation of circular preccession of spins, have been offered as a way to replace electric currents as information carriers. The overwhelming advantage being the lack of moving charges and Ohmic losses. In this context, the search for an efficient method of detection of becomes crucial. Nitrogen vacancy centers in diamond offer a highly sensitive and effective solution. These diamond lattice defects have quan- tum and optical features allowing them to be used to quantify the surrounding magnetic field. This project is composed of a theoretical study of spin waves followed by an experimental section where AC magnetometry is tried out as a detection method. First the computations for the dispersion relation of spin waves in a ferro- magnetic material where done. A simplified version assuming homogeneity in one direction is presented and then an expansion considering a wave mode of the first order in the previously constant direction is attempted. An analysis on the efficiency of spin wave generation outlines the conditions on the wavelength and the po- larisation needed to correctly drive spin waves while being able to measure them using NV centers. Then the experimental setup and steps of AC magnetometry are layed out. The results of a measurement are shown and are in alignment with the theoretical predictions, proving this to be a valid method.

Spin waves are the elementary excitations of magnetic materials. They are interesting because of their rich physics and potential role in low-dissipation information technology. To better understand spin-wave transport and explore new ways to control it, this thesis focuses on developing magnetic-imaging techniques based on the single spin of the nitrogen-vacancy (NV) defect in diamond that detects spin waves via their magnetic stray fields. These fields decay evanescently on the scale of the spin wavelength. By using NV centres embedded in an atomic force microscope probe that provides nanometre NV-sample proximity, we achieve sensitivity to nanoscale spin waves.

Magnons are quanta of spin waves, i.e. modes of collectively precessing spins. Thermally excited magnons in thin magnetic films generate stray fields at the film surface which can be detected using nitrogen-vacancy (NV) centers. NVs are lattice defects in diamond and are able to couple with magnon stray fields. Assuming a thermal occupancy of magnon modes, we study the magnetization dynamics of magnons propagating through thin magnetic insulators using the Landau-Lifshitz-Gilbert equation. We implement a numerical model to predict and understand the response of the NV center to proximal magnons in thin films. We investigate how the NV relaxation rate changes for different NV orientations by extending and generalizing the existing theory on chiral magnetic noise, and simulate an experimental setup for an NV placed just above the surface of a thin magnetic insulator. The simulation includes a static bias field in an arbitrary orientation with respect to the quantization axis of the NV center using the diamond's tetrahedral symmetry. This extended model is in demand due to limitations in present-day measurement techniques to align the bias field with an NV center. We use it to detect magnons that contribute to the relaxation rate of the NV, and determine an NV-to-film distance of 0.28(3) μm, from measured relaxation rates of an NV center placed above an yttrium-iron-garnet film with a thickness of 235(10) nm. Our model is available as an open-source Python module.