MAGNETIC-FIELD TUNING OF PARAMAGNETIC FREQUENCY-TEMPERATURE COMPENSATION IN CRYOGENIC SAPPHIRE DIELECTRIC MICROWAVE RESONATORS

Paramagnetic impurities present in sapphire dielectric microwave reson ators can provide frequency-temperature compensation at liquid-helium temperatures. We demonstrate a method for 'tuning' this frequency-temp erature compensation by applying a uniform magnetic field parallel to the resonator axis, which induces Zeeman splitting of the electron par amagnetic resonances. This was shown for a mode at 11.84 GHz, which li es between the Cr3+ and Fe3+ electron paramagnetic resonances present in a resonator cut from Union Carbide sapphire. However, the apparent frequency dependence of the Ca3+:alpha-Al2O3 and Fe3+:alpha-Al2O3 para magnetic susceptibilities in this dilute paramagnetic system did not o bey the expected theory.