Phase-Sensitive Imaging of Ferromagnetic Resonance Using Ultrafast Heat Pulses

Measuring local magnetization dynamics and its spatial variation is essential for advancements in spintronics and relevant applications. Here we demonstrate a phase-sensitive imaging technique for studying patterned magnetic structures based on picosecond laser heating. With the time-resolved anomalous Nernst effect (TRANE) and extensions, we simultaneously image the dynamic magnetization and rf driving current density. The stroboscopic detection implemented in TRANE microscopy provides access to both amplitude and phase information of the ferromagnetic resonance (FMR) and rf current. Using this approach, we measure the spatial variation of the Oersted driving field angle across a uniform channel. In a spatially nonuniform sample with a cross shape, a strong spatial variation for the rf current as well as FMR precession is observed. We find that both the amplitude and the phase of local FMR precession are closely related to those of the rf current.