Hexagonal Ferrites at Millimeter Wavelengths

Hexagonal ferrites may show a renaissance as candidates for various microwave devices in the millimeter wavelength range if perfect and low-loss materials, either bulk crystals or epitaxial layers, can be grown. Use is made of the large anisotropy fields of compounds with uniaxial magnetic anisotropy. These intrinsic anisotropy fields together with the applied external field provide the condition for FMR at these high frequencies. A survey is given of the current state of the technology. Since the feasibility of growing large and perfect hexagonal substrate crystals has been demonstrated increased effort in the deposition technology is justified, since not only microwave but also bubble applications can be envisaged.