Synthesis behavior and magnetic properties of Mg-Ni co-doped Y-type hexaferrite prepared by sol-gel auto-combustion method

Nano crystalline Y-type hexaferrites with chemical composition of Sr2Co2−xMgx/2Nix/2Fe12O22 (x of 0-0.6) were prepared by sol-gel auto-combustion technique at the temperature ranging from 900 to 1150 °C. The prepared samples were characterized by differential thermal analysis (DTA), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive spectrometer (EDS), and vibrating sample magnetometer (VSM). The results demonstrated that single phase co-doped Y-type hexaferrites with space group of R3/m were prepared at 1000 °C and crystallite size of the samples was calculated in the range of 45-63 nm. Also, below this temperature, some intermediate phases such as hematite, spinel ferrite, and SrO were observed. All of the synthesized hexaferrites showed homogeneous distribution and hexagonal platelet-like shapes which were suitable for microwave absorption. Hysteresis loop measurements revealed that the presence of hematite as a second phase caused a reduction in the saturation magnetization. Moreover, it was observed that, with increasing the calcination temperature to above 1000 °C, saturation magnetization demonstrated no significant changes while coercivity reduced from 950 to 250 Oe, which was due to transition from single to multi domain structures.