Impedance and modulus spectroscopy studies of cobalt substituted strontium hexaferrite ceramics

A series of strontium ferrites SrCoxFe12−xO19 (SFCO) with the chemical composition x = 0.0, 0.1, 0.2 & 0.3 have been synthesized by sol–gel method. The preliminary structural studies were carried out by X-ray diffraction technique, which shows the formation of polycrystalline sample with M-type structure and hexagonal symmetry of SFCO system. X-ray diffraction patterns confirms that no phase change is observed by the substitution of cobalt in SFCO up to x = 0.3. Using complex impedance spectroscopy technique, the complex impedance (Z*) and modulus (M*) properties of the materials were studied in the frequency range 20 Hz–40 MHz and temperature range 273–573 K. Impedance analysis indicates the presence of bulk resistive (grain) contributions which are found to decrease with increase in temperature showing the negative temperature coefficient of resistance (NTCR) behaviour indicating a typical semiconductor property of the ferrite material. In complex modulus spectrum, the grains have a dominant effect and also support their NTCR type behaviour. Both the complex impedance and complex modulus plots confirm the presence of non-Debye type of relaxation in the materials.