Ba and Sr ferrites are prepared by sol-gel technique with different Fe/Ba(Sr) ratios in the starting materials. Magnetization, coercive, and anisotropy field strength are determined depending on the heat treatment of the gel and the iron/barium(strontium) ratio in the starting material. A two-step heat treatment is used to prepare single-domain powders with high magnetization. These powders prepared by sol-gel technique show single-domain behavior with specific magnetization σS=649 A cm2/g and coercive field strength HcM=402 kA/m in the case of Ba ferrite and σS=695 A cm2/g and HcM=416 kA/m for Sr the ferrite. Al-substituted ferrites with high anisotropy field strengths are prepared additionally. Ferromagnetic resonance absorption is used to determine the anisotropy field strength and to investigate the formation process of the hexaferrite phase during the heat treatment. The beginning of hexaferrite formation occurs at annealing temperatures below 700 °C.

No abstract

No abstract

No abstract

Barium hexaferrite particles prepared by sol-gel technique yield best magnetic characteristics if a large barium surplus is used. Therefore, the powder sample has to be etched after the annealing process in order to get samples without intermediate phases. The used temperatures below 900°C and times shorter than 1h cause nanocrystalline hexaferrite particles with a specific saturation magnetization above 700 Acm2/g and a coercivity up to 470 kA/m