Preparation, Characterization, and Microwave Absorption Properties of Cobalt-Doped SrFe12O19 Nanoparticles

Ferrite is the major absorbing components of conventional radar absorbing materials (RAM). However, conventional RAM made of the single-absorbing components cannot meet the comprehensive requirements of “thin, wide, light, and strong.” To overcome this limitation, a composite compound of cobalt-doped SrFe 12 O 19 nanoparticles is currently exploited to improve absorbing ability. SrFe 12− x Co x O 19 (x = 0, 0.05, 0.1, 0.15, 0.20, 0.25) composite ferrites were prepared using the sol-gel method. Results show that the powders obtained are pure lead-magnetite ferrite, and the properties of the samples are improved evidently after Co substitution. At room temperature, the samples substituted using Co exhibit typical permanent magnetism. When x = 0.2, the maximum saturation magnetization and coercivity of the powders are 55.8 A· 2 /kg and 302.4 kA/m, respectively. The real complex permittivity part of SrFe 12− x Co x O 19 first increases and then decreases with the increase in x and has a maximum value of x = 0.2. The complex imaginary permittivity part fluctuates with the increase in x; it first decreases, then increases, and finally decreases. With the increase in x, the complex permeability real part of the sample does not change much between 2 GHz to 16 GHz but first increases and then decreases in the range of 16-18 GHz. The imaginary part of the complex permeability first increases and then decreases, reaching its maximum at x = 0.2. The attenuation constants and absorbing properties of the samples before and after substitution were analyzed. The matching thickness of strontium ferrite (SrFe 12 O 19 ) is 5.2 mm, the matching thickness of SrFe 11,8 Co 0.2 O 19 (x = 0.2) is reduced to 2.4 mm, the minimum reflectivity is −24.7 dB (13.8 GHz), and the microwave absorption bandwidth lower than −10 dB is 4.7 GHz (11.6-16.3 GHz). These results indicate that an appropriate amount of Co substitution could greatly improve the absorbing performance of SrFe 12 O 19 . This study provides a simple method for the preparation of Co doped strontium ferrite. The microwave absorbing properties of the composite powders are excellent and have potential engineering application value.