Effects of Zr-Zn Doping on the Properties of Strontium Hexaferrite (SrZrxZnxFe12-2xO19) Synthesized by a Co-Precipitation Method

Sammanfattning

Radar absorbing materials (RAMs) are used in multiple military applications to avoid detection by radar systems. A promising material for radar absorption is the ferrimagnetic material strontium hexaferrite (SrFe12O19). The ferromagnetic resonance frequency of strontium hexaferrite is around 50 GHz and should preferably be around 8-12 GHz (in the X-band) for aviation applications. To overcome these issues, the structure can be doped with non-magnetic ions such as Zr4+ and Zn2+ to lower the absorption frequency. This master’s thesis investigates the co-precipitation synthesis of Zr-Zn doped strontium hexaferrite to evaluate the microwave absorbing properties in the 8-12 GHz frequency range. An optimized Fe3+/Sr2+ molar ratio of 11.7 was required in the synthesis to give phase pure strontium hexaferrite. Three doping concentrations were evaluated with x = 0.8, 1.0 and 1.2, where x represents the amount of Zr4+ and Zn2+ substituting Fe3+ in the chemical formula SrZrxZnxFe12-2xO19. Sample plates were made with the doped strontium hexaferrite together with a cement matrix which were analyzed with a Naval Research Laboratory (NRL) arch. The sample with doping concentration x = 1.0 showed the highest reflection loss (RL) value and it occurred in the X-band at 10.83 GHz. The absorption of the x = 1.2 sample was similar but slightly lower and the x = 0.8 sample had its peak absorption in the Ku-band but still covering parts of the X-band. This study shows that strontium hexaferrite with a Zr-Zn doping concentration of around x = 1.0 is promising as a RAM for X-band absorption. Although, a higher concentration of ferrite powder in the sample plates would be needed for effective microwave absorption.