Imaging nanoscale magnetization 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 table-top techniques. To break free of the far-field diffraction limit, we have developed a near-field magnetic microscope based on magneto-thermo interactions: the time-resolved anomalous Nernst effect and the time-resolved longitudinal spin Seebeck 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 sub-100 nm spatial resolution from imaging current density around a nano-constriction. 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.