Crystallographically Textured and Magnetic LaCu-Substituted Ba-Hexaferrite with Excellent Gyromagnetic Properties

Excellent gyromagnetic properties of textured, bulk Ba-hexaferrite samples are required for low-loss, self-biased applications for microwave and millimeter-wave (MMW) devices. However, conventionally processed bulk Ba-hexaferrite ceramics typically demonstrate low remanent magnetization values, 4πM(r), of 2.0~3.0 kG, and relatively large ferromagnetic resonance (FMR) linewidths, ΔH(FMR), of 0.8~2 kOe. These properties lead to the development of high-performance, practical devices. Herein, crystallographically textured Ba-hexaferrite samples, of the composition Ba(0.8)La(0.2)Fe(11.8)Cu(0.2)O(19), having excellent functional properties, are proposed. These materials exhibit strong anisotropy fields, H(a), of ~14.6 kOe, high remanent magnetization, 4πM(r), of 3.96 kGs, and a low ΔH(FMR) of 401 Oe at zero-bias field at the Q-band. Concomitantly, the broadband millimeter-wave transmittance was utilized to determine the complex permeability, μ*, and permittivity, ε*, of textured hexaferrites. Based on Schlöemann’s theory of complex permeability, μ*, the remanent magnetization, 4πM(r), anisotropy field, H(a), and effective linewidth, ΔH(eff), were estimated; these values agree well with measured values.