Microwave Characteristics of Fine-Grain High-Power Garnets and Spinels

Abstract

One approach in materials engineering to increase the nonlinear power absorption threshold of ferrimagnetic materials is that of reducing the grain size. A program is described wherein this has been successfully carried out. The use of hot pressing techniques provides dense small‐grain materials suitable for device construction and evaluation. The method has proven equally successful for both garnet and spinels. An order of magnitude increase in threshold is readily achievable with no increase in low‐power insertion loss. Measurement of linewidth (ΔH), gyromagnetic ratio (γ), dielectric constant (ε′), loss tangent (tan δ), saturation magnetization (4πM_s), coercive force (H_c), spin‐wave linewidth (ΔH_k), and high‐power threshold values are given. The predominant effect of reduced grain size is to increase the spin‐wave linewidth (ΔH_k), which explains the measured increase in threshold. Case histories of application of fine‐grain materials in production devices are given as well as laboratory studies of both device performance and ΔH_k measurements.