Preparation, Magnetic And Microwave Absorbing Properties Of CoFe₂O₄ And SrFe₁₂O₁₉ Composites

More and more attention was paid to ferrite materials in the field of absorbing materials due to their low price, high absorption rate and thin coating. However, high density and narrow absorbing bandwidth markedly limits their application in absorbing field. Thus, the modified ferrites became a hot field of scientific research. The current research mainly focused on ferrites doped with rare-earth elements and ferrites composite with other materials. In this paper, some studies were done as follows.Cobalt ferrite powders were prepared via hydrothermal method and the effects of preparation conditions on the structures, morphologies and magnetic properties were studied. SEM results showed that the as-prepared samples under different reaction conditions had some agglomeration and they can be alleviated by improving reaction temperature and reaction time. VSM results showed that reaction temperature had greater influence on magnetic properties of cobalt ferrite. Saturation magnetization, coercivity and residual magnetization significantly increased with the increase of reaction temperature. With the increase of reaction time, saturation magnetization and residual magnetization increased firstly and then decreased, while coercivity decreased firstly and then increased.La³⁺and Y³⁺ were doped in cobalt ferrite powders respectively, and the influence of doping contents on structures, morphologies and magnetic properties was studied. XRD results showed that solubility of La³⁺ and Y³⁺ was x=0.10 and x=0.20 respectively, and impurity phase La?OH?3 and Y?OH?3 appeared when exceeded solubility. Cobalt ferrite doped with La³⁺ and Y³⁺ in the range of its solubility can refine grain and out of it can cause grain size increased. FT-IR spectra results indicated that Fe3+ of cobalt ferrite was substituted by La3 + and Y3 + in B sites. VSM results revealed that cobalt ferrite doped with La³⁺ and Y³⁺ can reduce saturation magnetization, while coercive decreased within the range of solubility and increased beyond the range of solubility.CoFe₂O₄/PANI composites were synthesized via in-situ polymerization method successfully, and the influence of cobalt ferrites' contents on structures, morphologies and magnetic properties was studied. XRD results showed that grain size of cobalt ferrites became smaller after coated with polyaniline. VSM results showed that saturation magnetization, remanent magnetization and coercive increased with the increase of cobalt ferrites' contents in the composites. Vector network analyzer results showed that when the mass ratio of Co Fe2O4 versus C6H5NH2 was 1:4, microwave absorbing properties were best, and the maximum of refection loss can reach-4.0 d B at the thickness of 3 mm and moved to lower frequency.SrFe₁₂O₁₉/PANI composites were prepared via in-situ polymerization method successfully, and the influence of strontium ferrites' contents on structure, morphology and magnetic properties was studied. XRD results showed that strontium ferrites' diffraction peak intensity increased with the increase of strontium ferrites' contents in the composites. VSM results showed that saturation magnetization, remanent magnetization increased with the increase of strontium ferrites' contents in the composites. Vector network analyzer results showed that the maximum of reflection loss was improved from-11.5 d B to-13.9 d B and the bandwidth over than-5 d B was increased from 2.0 GHz to 2.5 GHz at the thickness of 3 mm, when the mass ratio of Sr Fe12O19 versus C6H5NH2 was =1:4.