Enhanced gyromagnetic properties and loss reduction of highly-dense NiCuZn ferrite for millimeter-wave applications

Prior studies predominantly utilized solid-state sintering to fabricate Ni-based ferrite ceramics, aiming to enhance magnetic properties. While some researchers have adopted the hot-pressing method for preparing these ceramics, the resultant porosity remained elevated (>2 %), leading to an increased ferromagnetic resonance linewidth (Δ H ). The impact of high temperature and pressure during the forming process on Δ H and gyromagnetic properties in nickel-based ferrite ceramics has been seldom explored using hot pressing. Building on prior research involving solid-state sintering of Ni-based ferrite, this study employed a vacuum hot-pressing sintering technique to further optimize the gyromagnetic properties of the ferrite. A systematic investigation was conducted to understand the influence of porosity, grain size, and microstructure on the magnetic attributes of Ni ferrite ceramics. Under conditions of high pressure (48 MPa) and zero holding time, as the hot-pressing sintering temperature rose from 800°C to 1050°C, the average grain size expanded from 0.4 μm to 3.36μm. Concurrently, the relative density and saturation magnetization initially increased before decreasing. Consequently, a NiCuZn ferrite characterized by uniform, dense grains (GS ave =1.94 μm and D r =99.2 %) and good gyromagnetic properties (4π M s =4703 Gs and Δ H =277 Oe) was achieved through hot-pressure sintering at approximately 950°C.