Using scanning plasmonic heating for nanoscale imaging of magnetization

Advanced magnetic microscopies are key to advancing our understanding and application of novel magnetic phenomenon such as skyrmions, spinwaves, and domain walls. However, due to the diffraction-limit of light, achieving the 10-100 nanometer spatial resolution and 10 – 100 picosecond temporal resolution required to image these phenomenon is beyond the reach of table-top techniques. To break free of the far-field diffraction limit, we have been developing a near-field magnetic microscopy based on magneto-thermo interactions: the time-resolved anomalous Nernst effect and the time-resolved longitudinal spin Seebeck effect. This technique uses picosecond pulsed excitation of surface plasmon polaritons which are nanofocused to the apex of a scanning tip. The resulting near-field tip-sample interaction excites a nanoscale thermal gradient for magneto-thermal microscopy. We present sub-optical diffraction spatial resolution and picosecond temporal resolution in proof-of-concept experiments. 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.