Synergic effect of additives on the structure and properties of nano strontium hexaferrite synthesized via the gel combustion method

Abstract

Strontium hexaferrite (SrFe12O19) is a ferrimagnetic oxide that is widely used as a permanent magnetic material due to its excellent magnetic properties and low production cost. Modification of chemical composition and nanoscale structural refinement can improve its properties. In the present study, the synthesis process of strontium hexaferrite by the gel combustion method was investigated. SrFe12O19 was synthesized with the iron to strontium ratio of 10-12. The calcination temperature was also optimized by modifying this ratio. The effect of adding cobalt, manganese, zirconium, and zinc cations to the composition of SrFe12-2x(Mn Co Zn)x/3ZrxO19 (x = 0.0–1.0) was investigated. The samples were characterized by X-ray diffraction (XRD), thermal analysis (TGA/DTA), field emission scanning electron microscopy (FE-SEM), vibrating sample magnetometer (VSM), and vector network analyzer (VNA). The results showed that, in the free-additive samples, the pure strontium hexaferrite phase was formed only under the optimal conditions where the iron to strontium ratio and heat-treatment temperature were about 11 and 900 °C, respectively. In this case, clustered particles with the size of 64-145 nm were observed in the structure. In addition, partial substitution of different amounts of manganese, cobalt, zinc, and zirconium cations for Fe3+ in the hexaferrite structure affected its magnetic properties, such as saturation magnetization (Ms), remnant magnetization (Mr), coercivity (Hr), and Mr/Ms ratio. The dielectric constant, reflectance, transmittance, and absorption of electromagnetic waves were also changed. The sample with x = 0.8 showed the maximum reflectance (36.20%) and minimum transmittance (54.10%). The sample with x = 0.4 showed the desired reflectance loss of −9.24 dB at the frequency of 12.15 GHz.