Hexagonal Ferrites for Use at X- to V-Band Frequencies

Abstract

A series of uniaxial materials has been prepared and studied in which the effective anisotropy field can be controlled and varied over the range of 0 to 12 700 oe. The materials are solid solutions of the NiW and CoW compounds and have the chemical formula BaO·2[Ni1−xCoxO]·7.8Fe2O3 with x varying from zero, where the anisotropy field is 12 700 oe, to 0.5 where the anisotropy field is vanishingly small. The temperature dependence of the net resultant anisotropy field, linewidth, and g factor of these materials is discussed. By using oriented polycrystalline samples of these materials, the effective internal anisotropy field can be used to augument external applied fields. Different materials of this series have been used to construct resonance isolators at V- and K-band frequencies with bandwidths of the order of 20% and peak isolation ratios of greater than 30 to 1.