Generation of spin currents by the orbital Hall effect in Cu and Al and their measurement by a Ferris-wheel ferromagnetic resonance technique at the wafer level

We present a ferromagnetic resonance (FMR) method that we term the ``Ferris'' FMR. It is wideband, has at least an order of magnitude higher sensitivity as compared to conventional FMR systems, and measures the absorption line rather than its derivative. It is based on large-amplitude modulation of the externally applied magnetic field that effectively magnifies signatures of the spin-transfer torque making its measurement possible even at the wafer level. Using the Ferris FMR, we report the generation of spin currents from the orbital Hall effect taking place in pure Cu and Al. To this end, we use the spin-orbit coupling of a thin Pt layer introduced at the interface that converts the orbital current to a measurable spin current. While Cu reveals a large effective spin Hall angle exceeding that of Pt, Al possesses an orbital Hall effect of opposite polarity in agreement with the theoretical predictions. Our results demonstrate additional spin- and orbit functionality for two important metals in the semiconductor industry beyond their primary use as interconnects with all the advantages in power, scaling, and cost.