Microwave modes of two dimensional electron systems near macroscopic ferromagnets*

We report on microwave measurements of a high mobility two dimensional electron system (2DES) in a homogenous external field B$_{0}$, and with cylindrical ferromagnets of radii r$_{m}$ placed on the surface of the sample with the long axis perpendicular to the 2DES. The magnet materials are Dy and permalloy, and r$_{m}$ varies from 0.5 mm to 0.125 mm. Microwave spectra measured for transmission between two ohmic contacts show resonant absorption at peak frequency, f$_{pk}$, decreasing as B$_{0 }$or r$_{m }$increase. We will interpret the data in terms of plasma excitations similar to edge magnetoplasmons [1] confined under the edges of the magnets by the large magnetic field gradients there. [1] See, for example, V. A. Volkov and S. A. Mikhailov, Sov. Phys.-JETP \textbf{67}, 1639(1988).