| Hexaferrites have been widely used in microwave and millimeter wave devices as permanent magnets and as gyromagnetic materials, e.g., in circulators, filters, isolators, inductors, and phase shifters. As a critical component in radar and modern wireless communication systems, it is the microwave circulator that has drawn much attention. Many efforts have been made to design light and miniature circulators with self-biased ferrite materials. We report the magnetic and structural properties of a series of W-type barium hexaferrites of composition BaZn2-xCoxFe16O27 where x=0.15, 0.20, and 0.25. The anisotropy field of these BaW ferrites decreased with the substitution of divalent Co ions, while, they maintained crystallographic c-axis texture. The measured anisotropy field was ~10 kOe, and a hysteresis loop squareness Mr/Ms=79% was obtained due to well-controlled grain size within the range of single domain scale. U-type barium hexaferrite thin films were deposited on (0001) sapphire substrates by pulsed laser deposition. The results indicate a measured anisotropy field of ~8 kOe, and the saturation magnetization (4piMs) of 3.6 kG. More interestingly, an optimal post-deposition annealing of the films results in a strong (0, 0, n) crystallographic texture and a high squareness (Mr/Ms= 92%) out of the film plane. Furthermore, the highly self-biased ferrite films exhibited low FMR linewidth of ~200 Oe.;Improved performance and miniaturization are needed to meet the ever-increasing demands of devices used in ultra-high frequency (UHF), L-band, and S-band, which are of particular interest in a variety of commercial and defense related applications. Utilizing materials possessing high permeability and permittivity with low magnetic losses is a promising solution. As a critical component in radar and modern wireless communication systems, antenna elements with compact size are constantly sought. Ferrite composites of the nominal composition Ba3Co2+xIrxFe24-2xO41 were studied in order to achieve low magnetic and dielectric losses and equivalent permittivity and permeability over a frequency range of 0.3-1 GHz. Crystallographic structure was characterized by X-ray diffraction, which revealed a Z-type phase accompanied by increasing amounts of Y-type phase as the iridium amount was increased. The measured microwave dielectric and magnetic properties showed that the loss tandeltaepsilon and loss tandeltamicro were decreased by 80% and 90% at 0.8 GHz with the addition of iridium having x =0.12 and 0.15, respectively. An effective medium approximation was adopted to analyze the composite ferrites having mixed phase structures. Moreover, adding Bi2O3 resulted in equivalent values of real permittivity and real permeability over the studied frequency range. The resultant data gives rise to low loss factors (i.e., tandeltaepsilon/epsilon' = 0.008 and tandelta micro/micro'=0.037 at 0.8 GHz) while characteristic impedance was the same as that of free space impedance. |
