High-frequency signal processing using ferromagnetic metals

We present results for tunable microwave band-stop and bandpass filters on a microstrip geometry. These structures, prepared by sputtering on GaAs substrates, are compatible in size and growth process with on-chip high-frequency electronics. For the notch filters, we observed power attenuation up to ∼100 dB/cm and an insertion loss on the order of ∼2-3 dB for both Permalloy- and Fe-based structures. The operational frequency ranges from 5 to 35 GHz for external fields below 5 kOe. We discuss methods to increase operational frequency and reduce device linewidth. Using these techniques we are able, for example, to obtain an operational frequency of 11GHz at zero applied field and to narrow the device linewidth from 3 GHz to 330 MHz. The operational frequency, which can be obtained from the ferromagnetic resonance condition, is set by material properties such as saturation magnetization M_s, anisotropy fields, the gyromagnetic ratio, and the magnitude of an applied field H. Thus, by using different materials and external fields one can create devices which function over a wide range of frequencies.