Ferromagnetic resonance phase imaging in spin Hall multilayers

We experimentally image the magnetic precession phase of patterned spin Hall multilayer samples to study the rf driving field vector using time-resolved anomalous Nernst effect microscopy. Our ferromagnetic resonance (FMR) measurements quantify the phase and amplitude for both the magnetic precession and the electric current, which allows us to establish the total driving field orientation and the strength of the spin Hall effect. In a channel of uniform width, we observe a large spatial variation of the FMR phase laterally across the channel. We interpret our findings in the context of electrical measurement using the spin transfer torque ferromagnetic resonance technique and show that observed phase variation introduces a systematic correction into the spin Hall efficiency if spatial phase and amplitude variations are not taken into account.