Low-loss barium ferrite quasi-single-crystals for microwave application

Barium hexaferrites (BaFe12O19) are especially useful for microwave/millimeter devices. Due to large ferromagnetic resonance (FMR) loss (linewidths > 2 kOe), traditional compacts of polycrystalline Ba ferrites indeed hinder the utilization of the materials for practical devices. The present experiment demonstrates that the quasi-single-crystal Ba ferrite disks can be fabricated by a single solid-state reaction technique without liquid phase participation, combining with a processing of alignment for the ferrite seed crystals. The ferrite bulks show a pure hexagonal Ba ferrite phase, an expected 4 pi M-s of 4.48 kG, and coercivity of 10 similar to 20 Oe along the c axis, similar to the results of a typical single crystal. The FMR measurement indicates that the sample yields an anisotropy field of 16.0 kOe and a linewidth of about 300 Oe at U-band frequencies. Although the linewidth is broader than ideal Ba ferrite single crystals (Delta H < 100 Oe), it may be possible to reduce to 100 Oe by eliminating pores, cracks, local grain boundary, and nonuniformity. In terms of material preparation, we believe that it is cost effective in the production of future microwave devices. (c) 2007 American Institute of Physics.