Investigation of nickel and manganese substitutions on the microwave absorption and magnetic properties of hexaferrite strontium nanoparticles prepared by sol–gel auto-combustion method

In this study, M-type hexaferrite strontium nanoparticles with a chemical formula of SrFe_12-x(ZrCo_0.5M_0.5)_0.5XO₁₉ were successfully synthesized by sol–gel auto-combustion method. This material is potentially used in microwave absorber devices, such as antenna, wearable health monitoring systems, and flexible displays. The substitution effects of Fe³⁺ by Ni²⁺, and Mn²⁺ ions with varying contents (x = 0.4, 0.8, 1.2) on the structural features, bond situation, particles morphology, and magnetic properties of nanoparticles were investigated. To analyze these changes, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Field emission scanning electron microscopy (FE-SEM), and vibrating sample magnetometer (VSM) analysis were used, respectively. The result of XRD showed the formation of hexaferrite strontium phase. The average particle size for the samples determined by Field emission scanning electron microscopy (FE-SEM) was less than 100 nm. The optimal level of saturation magnetization (M_s) and coercivity (H_c) for the sample doped with Mn was found to be 70.02 emu/g and 4875 Oe, respectively (for X = 0.4). However, for the sample doped with Ni, these parameters were found to be 73.40 emu/g and 3770 Oe, respectively (for X = 0.8). Finally, the synthesized nanoparticles were coated with poly(o-toluidine) (POT) in order to study reflection loss (RL) by vector network analyzer (VNA). The results showed a considerable microwave absorption for Mn and Ni nanocomposites by X = 1.2.