On-chip coplanar stripline for micron-scale ferromagnetic resonance and spin pumping devices*

Ferromagnetic resonance (FMR) spin pumping is a rapidly growing field. While previous measurements have focused on large-scale ($\sim$mm) devices, dimensions will need to be reduced to prove useful for applications. On-chip microwave structures offer a solution to this by providing localized microwave fields that can be used to resonate small device geometries while leaving them easily accessible for electrical connections, as opposed to the ``flip-chip'' or resonant cavity methods. Using a shorted coplanar strip (CPS) waveguide, we perform broadband (6-12 GHz) FMR measurements in a permalloy bar of dimensions 20$\mu$m x 1$\mu$m x 20nm--too small to be detected by measuring microwave reflections from a cavity. FMR is detected in the permalloy strip through changes in the anisotropic magnetoresistance [1]. This scheme allows for quantitative characterization of magnetization dynamics and microwave fields. These findings demonstrate that on-chip microwave structures will enable new, smaller device geometries and measurement possibilities for a variety of spin pumping systems.\\[4pt] [1] M. V. Costache, et. al, Appl. Phys. Lett. 89, 232115 (2006).