Hexagonal SrFe12O19 ferrites: Hydrothermal synthesis and their sintering properties

► SrM ferrites are hydrothermally synthesized under a pressure less than 1 MPa. ► SrCO3 forms inevitably in the hydrothermal process. ► Perovskite SrFeO3−x forms in specimens after sintering at 1100 °C. ► Pure SrM ferrite forms after sintering at 1200 °C. ► The magnetic properties are enhanced after sintering at high temperatures.