| Summary: | 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 BaZn<sub>n2-x</sub>Co<sub>x</sub>Fe<sub>16</sub>O<sub>27</sub> 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
M<sub>r</sub>/M<sub>s</sub>=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 (4πM<sub>s</sub>) 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 (M<sub>r</sub>/M<sub>s</sub>= 92%) out of the film plane. Furthermore, the highly self-biased ferrite films exhibited low FMR linewidth of ~200 Oe.
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