The magnetic properties of the U-type ferrite synthesized by a sol-gel process had studied by substituting cobalt with manganese or zinc in cobalt-based U-type ferrite. The substituted U-type ferrite showed a dominant crystal structure at a different substitution ratio of manganese and zinc. The change of the starting temperature of U-type ferrite formation according to substitutional elements was confirmed by TG-DTA analysis. In the case of manganese substitution, the starting temperature of U-type ferrite formation lowered, and on the contrary, when zinc was substituted, it became higher. The magnetic properties of the U-type ferrite substituted with manganese showed a tendency that the saturation magnetization was decreased and the coercivity was increased as the manganese ratio increased. The highest saturation magnetization was 57.9 emu/g in the specific composition (Ba4Co0.5Zn1.5Fe36O60) substituted with zinc.
U-type ferrite typified by Ba4Co2Fe36O60 is used as a RAM (Radar Absorbing Materials) in the X-band (8-12 GHz). Ba4Co2Fe36O60 is known to have a complex crystal structure, which makes it difficult to obtain single phase and have low reproducibility. Previously known U-type ferrites have been fabricated based on a ceramic process that mixing (by a ball mill), calcining, grinding, binder mixing, drying, sieving, pressing and sintering. In contrast, the process of preparing the powder by the sol-gel method and its heat-treating is advantageous in that it can reduce the process steps and the required time. In addition, the precise stoichiometric control by the sol-gel method can effectively evaluate the effect of added or substituted elements. In this study investigates the crystal structure of Ba4Co2Fe36O60 synthesized by the sol-gel method and the morphology of U-type ferrite nano-powders according to various heat treatment conditions. Analysis of the crystal structure is used for XRD. Morphology and size are observed by SEM. In addition, VSM is performed to confirm the change of magnetic properties according to various heat treatment conditions.