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.