Lowered ferromagnetic resonance linewidth and enhanced spin wave linewidth of nickel-based ferrite ceramics using hot-pressing method.

Previous investigations commonly employed solid-state sintering to fabricate Ni-based ferrite ceramics to improve magnetic performance. A few researchers used the hot-pressing method to prepare Ni-based ferrites, but their porosity remained relatively high values (>2%), resulting in high ferromagnetic resonance line widths (Δ H). To date, the influence of high-temperature and high-pressure forming processes on Δ H and spin wave line width (Δ H k) in Ni-based ferrite ceramics has been rarely reported using hot pressing. This study utilized a uniaxial hot-pressing method and systematically investigated the effect of porosity, grain size and grain uniformity on the magnetic properties of Ni-based ferrite ceramics. Porosity played a crucial role in determining Δ H at different sintering temperatures. As the sintering temperature increased, the reduced porosity resulted in a decrease in Δ H. Under varying sintering pressures, the grain uniformity primarily affected Δ H. Increasing pressures led to more uniform grains, causing a decrease in Δ H. The Δ H k was directly associated with the grain sizes. With the increase of sintering temperatures, the grain sizes increased, leading to a decrease in Δ H k. Conversely, as the pressure increased, the decreased grain sizes brought the increased Δ H k. Compared to other hot-pressing results on the Ni-based ferrite ceramics, the optimized high-temperature and high-pressure processing with annealing significantly reduced the porosity of Ni-based ferrite ceramics (0.11%). In comparison with the solid-state sintering without pressures, the optimized hot-pressed Ni-based ferrite ceramics exhibited a 7% increase in saturation magnetization, a 63% reduction in Δ H and a 6.5% increase in Δ H k. The striking reduction of Δ H suggests that microwave devices assembled from Ni-based ferrite ceramics could withstand high power levels while minimizing lower electromagnetic losses, predicting promising applications for Ni-based ferrite materials in high-power microwave ferrite devices. [ABSTRACT FROM AUTHOR]