Nanoscale magnetization and microwave current imaging using scanning-probe magneto-thermal microscopy*

High resolution, time-resolved magnetic microscopy is crucial for understanding novel magnetic phenomenon such as skyrmions, spinwaves, and domain walls. Currently, achieving 10-100 nanometer spatial resolution with 10-100 picosecond temporal resolution is beyond the reach of most table-top techniques. We have developed a near-field magnetic microscope based on the time-resolved anomalous Nernst effect. Our technique involves scanning a sharp gold tip within a near-field optical excitation. The resulting tip-sample interaction creates a nanoscale thermal gradient for magneto-thermal microscopy and its extension to imaging an applied current density. We study the characteristics of near-field thermal excitation with a picosecond laser and demonstrate magnetic imaging of a multi-domain state. We present below 100 nm spatial resolution from imaging current density around a nano-constriction, and picosecond temporal resolution enabling phase-sensitive dynamics studies. Our results suggest a new approach to nanoscale spatiotemporal magnetic microscopy in an accessible, table-top form to aid in the development of high-speed magnetic devices.