The development and current status of microwave ferrite technology is reviewed in this paper. An introduction to the physics and fundamentals of key ferrite devices is provided, followed by a historical account of the development of ferrimagnetic spinel and garnet (YIG) materials. Key ferrite components, i.e., circulators and isolators, phase shifters, tunable filters, and nonlinear devices are also discussed separately.

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The magnetic and structural properties of Fe films deposited by ion-beam sputtering (IBS) on (100)-oriented GaAs substrates are described. The films are between 30 and 600 nm thick and are characterized by a coercive field of approximately 3–6 Oe. The saturation magnetization and anisotropy field, inferred from vibrating sample magnetometer measurements agree substantially with the values expected for bulk Fe. Films deposited on the (100) substrate show the expected fourfold (or ‘‘biaxial’’) symmetry with no indication of a uniaxial anisotropy component. These properties make the films ideally suitable for the intended application in a hybrid semiconductor-magnetic memory, in which two magnetic remanent states with mutually orthogonal magnetization directions interact with an electronic flip-flop circuit.

The requirements for circulators for use in combination with microwave and millimeter-wave integrated circuits are reviewed, with special emphasis on modules for phased-array antennas. Recent advances in broadbanding and in miniaturization are summarized. Novel types of circulators that are fabricated by attaching a ferrite disc and a suitable coupling structure to the surface of a dielectric or semiconductor substrate ("quasi-monolithic" integration) are described. Methods for achieving complete monolithic integration are also discussed.

Highly anisotropic SmCo based films with the TbCu7-type structure have been sputter deposited directly onto YIG substrates. The SmCo crystallites have the c axes approximately randomly splayed about the substrate plane such that the easy direction of magnetization of the SmCo film is in the film plane. The in-plane static energy product of the SmCo film layers was about 16 MG Oe. In-plane vibrating sample magnetometer hysteresis loops of the SmCo film and YIG substrate exhibit a composite form with the YIG field reversal shifted into the first quadrant by the looping field from the SmCo film layer. Approximately 4×4 mm2 pieces of YIG substrate have been measured to determine the YIG bias field and field required for reverse saturation of the YIG as a function of the SmCo based film layer thickness to YIG substrate thickness. It is observed that for SmCo to YIG thickness ratios greater than 0.22, the looping field from the SmCo film layer is sufficient to saturate the YIG magnetization in the reverse direction. SmCo film thicknesses in the range from 80 to 120 μm have been used in these studies. Special boundary layers have been used to promote thick film adhesion to the YIG substrates.