Measurements of susceptibility due to paramagnetic impurities in sapphire using whispering gallery modes

The microwave susceptibility due to paramagnetic impurities in monocrystalline sapphire has been evaluated based on measurements of the resonant frequency shifts of several whispering gallery modes (WGM) from the normal to the saturated spin state. Spin saturation was achieved by employing a microwave source at a frequency close to the frequency of electron spin resonance for the specific paramagnetic ions. The microwave susceptibility due to the presence of Cr/sup +3/ ions was measured and it proved to be highly anisotropic having the dominant component in the plane perpendicular to the anisotropy axis (C-axis) of sapphire crystal.