Development of a System for Low Temperature Optical Measurement of Three-Dimensional Magnon, Plasmon and Spin Torque Transfer Dynamics

Spin-dependent phenomena in magnetic heterostructures and topological insulators (TIs) have attracted lots of attention from the perspective of both fundamental science and device development. For example, the spin orbital interaction in ferromagnet (FM)/heavy metal (HM) bilayers allows for all-electrical manipulation of magnetization. Moreover, the protected and linear-dispersed surface states of TIs leads to the unique spin-momentum locking. Despite extensive studies of these novel phenomena, there remain important questions about their underlying mechanisms. For example, the dynamics of these phenomena, which are critical for device applications, remain poorly understood. To address these important questions in the field, we have developed an experimental apparatus allowing ultrafast and quasi-DC optical study of magnon, plasmon, and spin orbit torque (SOT) in a wide variety of magnetic systems at low temperature and in the presence of a two-dimensional magnetic field. To benchmark the capability of this instrument, we present data demonstrating time-resolved Magneto-Optical Kerr Effect (TRMOKE) study of the SOT-driven magnetization dynamics in both Py/Pt and CoFeB/Ta bilayers.