Imaging weak magnetic fields on the nanometer-scale

The ability to map magnetic field sensitively and on the nanometer-scale – unlike global magnetization or transport measurements – overcomes ensemble or spatial inhomogeneity in systems ranging from arrays of nanometer-scale magnets, to superconducting thin films, to strongly correlated states in van der Waals heterostructures. Local imaging of nanometer-scale magnetization, Meissner currents, or current in edge-states is the key to unraveling the microscopic mechanisms behind a wealth of new and poorly understood condensed matter phenomena. I will discuss efforts in our group aimed at developing and applying high-sensitivity, high-resolution, non-invasive magnetic scanning probes. In particular, we have been developing nanometer-scale superconducting quantum interference devices fabricated at the apex of a scanning probe tip as well as ultra-sensitive magnetic force microscopy based on nanowire probes. I will discuss recent imaging experiments with these tools on few-layer van der Waals magnets, the surface of a bulk chiral magnet, and a ferromagnetic topological insulator, which yield new insights into their underlying magnetism.