Ultrafast Measurements of the Longitudinal Spin Seebeck Effect in Au/TmIG and Au/YIG

Spin transport between a magnetic insulator and a normal metal is an area of active research within the spin physics community to further the realization of spintronic devices. We investigate picosecond spin-currents across Au/TmIG and Au/YIG interfaces in response to ultrafast laser heating of the Au metal. In the picoseconds after heating, large interfacial spin currents occur due to a temperature imbalance between electrons and phonons in the metal, and magnons and phonons in the magnetic insulator. We utilize four different optical probes to develop a complete picture of the heat and spin transport in Au/TmIG and Au/YIG. Magneto-optic Kerr effect measurements of Au at a wavelength of 800 nm detects the spin accumulation in the normal metal that results from interfacial spin-currents. Magneto-optic Kerr effect measurements of the YIG/ TmIG at 400 nm monitor the ultrafast decrease in the magnetic moment of TmIG/YIG due to heating from Au electrons. Finally, thermoreflectance measurements at 450 and 950 nm monitor the temperature evolution of the Au electrons and phonons, respectively. Together, these measurements allow us to estimate the magnitude of the transport coefficients responsible for the longitudinal spin-Seebeck effect in these systems.