Using Picosecond Heat Pulses To Measure Magnetization

Abstract

Recent advances in nanoscale magnetism have demonstrated the potential for spin-based technology. Future engineering advances and new scientific discoveries will require research tools capable of examining local magnetization dynamics at length and time scales fundamental to magnetic systems, which is typically 10-200 nm and 5-50 ps. A key problem is that current table-top magnetic microscopy cannot access both of these scales simultaneously. In this thesis, we introduce a spatiotemporal magnetic microscopy technique which uses magneto-thermoelectric interactions to measure local magnetization via the time-resolved anomalous Nernst effect (TRANE). By generating a shortlived, local temperature gradient, the magnetic moment is transduced into an electrical signal. Experimentally, we show that TRANE microscopy has time resolution below 30 ps and spatial resolution limited by the thermal excitation area. Furthermore, we present numerical simulations to show that the thermal spot size sets the limits of the spatial resolution down to 50 nm. The thermal effects used for TRANE microscopy have no fundamental limit on their spatial resolution, therefore a future TRANE microscope employing a scanning plasmon antenna could enable measurements of nanoscale magnetic dynamics.