Correlation between coercive field and radiation attenuation in Ni and Mg ferrite doped with Mn and Co

• Manganese diffusion occurs in octahedral sites.
• Analysis by SEM and by Rietved shows agreement.
• The structure is the inverse spinel type.
• Low loss leads to obtain low radiation absorption.
• The Co addition gets high reflectivity and coincides with high coercivity.

It was investigated NiMg0.1MxFe2O4 ferrite where M stands for Mn, Co or simultaneously Mn and Co dopants. The concentration of M is 0.1 and it was divided by two in the sample with addition of Mn and Co. It was used the method of citrate precursors with 1100 °C calcination. The materials were characterized by X-ray diffractometer (XRD), scanning electron microscopy (SEM), vibrating sample magnetometer (VSM) and reflectivity measures by waveguide method. The X-ray diffraction measures, with Rietveld refinement, present average crystallite sizes between 0.576 and 0.626 µm. The SEM analysis shows clustered particles smaller than 1 µm at 1100 °C, in agreement with Rietveld refinement. The compositions with Mn reach magnetization between 42.09 and 53.20 Am2/kg, which does not generate high microwave absorption. The 0.1 Co addition reached greater coercivity (2.96×10−2 T), with up to 84% reflectivity at 10.17 GHz frequency. The Co material has high magnetocrystalline anisotropy, which is associated with the increase of coercive field, Hc. The higher coercivity optimizes the reflectivity results.