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 degrees 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 degrees 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 degrees 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. (C) 2016 Elsevier B.V. All rights reserved.