Microwave losses of nanostructure Li-Ni ferrites in X-band and Ku-band

The molar ratio(x) of Li-Ni ferrites in the formula Li0.5-0.5xNixFe2.5- 0.5xO4 was varied in range 0.1-1.0 by hydrothermal process. The XRD, SEM, and TEM tests were conducted to examine the samples crystalline phase and to characterize the particles shapes and sizes. The high purity spinel structure was obtained at med and high x values. SEM and TEM images showed the existence of different ferrite particles shapes like nanospheres and nanorods. The maximum particle size is around (20nm). These size encourage occurrence of super paramagnetic state. The reflection loss and insertion loss as microwave losses of Li-Ni ferrite-epoxy composite of 1mm thickness and mixing ratio 39.4 wt was investigated. The minimum reflection loss in x-band and in Ku band was about -8dB around 10GHz and lower than -18dB respectively. The insertion loss exceeded -6dB in the two band for some samples

Effect of pH on Structural, Magnetic and FMR Properties of Hydrothermally Prepared Nano Ni Ferrite

Nano nickel ferrite particles were prepared at pH values 1.5, 4, 7, 10, 13 by a hydrothermal method using metal chlorides and NaOH as an oxidant and solution basicity controller. There is a phase transition from hematite to spinel ferrite that begins when the pH reaches 4. The lowest crystallite size (4 nm) was associated with a highest lattice constant (8.345 Å), at pH=4. Whereas maximum crystallite size 64.5 nm corresponds lattice constant of 8.298 Å at pH=10. The highest magnetization (48 emu/g) value was achieved for the sample prepared at pH=7, which at the same time has a lower coercivity. The samples synthesized at pH ≥4 show superparamagnetic behavior owing to its low particle size and to zero field cooling and field cooling measurements. The ferromagnetic resonance (FMR) cavity tests analysis show that the broadened linewidth (770 Oe) and high imaginary permeability or high microwave absorption which is linked to high magnetization and low coercivity of superparamagnetic particles and their aggregation. There was a shift in the resonance field due to internal fields and cation distribution