Shahab Torkian - Materials Engineering Department, Malek Ashtar University of Technology, Shahin Shahr, Iran Ph.D. of Materials Science and Engineering.
Ali Ghasemi - Materials Engineering Department, Malek Ashtar University of Technology, ShahinShahr, Iran Associate Professor of Materials Science and Engineering.
Reza Shoja Razavi - Materials Engineering Department, Malek Ashtar University of Technology, ShahinShahr, Iran Associate Professor of Materials Science and Engineering.
Majid Tavoosi - Materials Engineering Department, Malek Ashtar University of Technology, ShahinShahr, Iran Assistant Pofessor of Materials Science and Engineering.

CoxNi۱-xFe۲O۴ ferrites (x=۰, ۰.۲, ۰.۴, ۰.۴, ۰.۶, ۰.۸ and ۱) were prepared by a sol-gelauto-combustion method. The samples were structurally characterized by X-raydiffractometry (XRD), field emission scanning electron microscopy (FE-SEM),energy dispersive X-ray analysis (EDX), and Fourier transform infrared spectroscopy(FTIR). The XRD patterns confirmed single phase formation of spinel structure.Cation distribution estimated from XRD data suggested the mixed spinel structure offerrite. The EDX analysis was in good agreement with the nominal composition. Theresults of FTIR analysis indicated that the functional groups of Co-Ni spinel ferritewere formed during the combustion process. According to FE-SEM micrographs, byaddition of cobalt ion the average particle size of substituted nickel ferrite wasgradually became smaller from ۴۵۰ nm to ۲۸۰ nm. Magnetic measurement usingvibrating sample magnetometer (VSM) showed an increase in saturationmagnetization and coercivity by Co۲+ substitution in nickel ferrite. ForCo۰.۸Ni۰.۲Fe۲O۴ sample, Ms and Hc reaches as high as ۹۳ emu/g and ۴۲۰ Oe,respectively. The reflection loss properties of the nanocomposites were investigatedin the frequency range of ۸ GHz to ۱۲ GHz, using vector network analyzer (VNA).Cobalt substitution could enhance reflection loss of NiFe۲O۴ ferrite. The maximumreflection loss value of the Co۲+ substituted Ni ferrite was ~ –۲۶ dB (i.e. over ۹۹%absorption) at ۹.۷ GHz with bandwidth of ۴ GHz (RL< – ۱۰dB) through the entirefrequency range of X-band.

Spinel ferrite, Cation distribution, Magnetic properties, Microwaveabsorption.