Structural and dielectric properties of doped ferrite nanomaterials suitable for microwave and biomedical applications

The sol-gel auto-combustion method was adopted to synthesize nanomaterials of single-phase X-type hexagonal ferrites with the composition of Sr2-xGdxNi2Fe28-yCdyO46（x=0.00,0.02,0.04,0.06,0.08,0.10 and y = 0,0.1,0.2,0.3,0.4,0.5）.The structural properties were carried out by XRD analysis and the lattice parameters show variation with the doping of Gd-Cd.The average particle size measured by TEM was in the range of 8-10 nm which is beneficial in obtaining suitable signal-to-noise ratio in recording media and biomedical applications.The room temperature resistivity enhanced with the increase of the dopant concentration.The increase in resistivity indicates that the synthesized materials can be considered good for the formation of the multilayer chip inductors（MLCIs） as well as for the reduction of eddy current losses.The dielectric constant decreased with the increase in the frequency which is the general reported trend of the hexagonal ferrites and can be explained on the basis of Koop’s theory and Maxwell-Wagner polarization-model.The abnormal dielectric behavior indicates the formation of small polarons in the material.The maximum value of tangent loss at low frequencies reflects the application of these materials in medium frequency devices（MF）.