Differences in the structure and magnetic properties of Sr1−xRExFe12O19 (RE: Pr and Dy) ferrites by microwave-assisted synthesis method

Sr1−xRExFe12O19 (RE = Pr, Dy; x = 0, 0.15, 0.25 and 0.5) hexaferrites were synthesized by sol-gel auto-combustion and microwave-assisted calcination route. The thermal decomposition process, structure and magnetic properties of the products were characterized by thermal differential scanning calorimeter (DSC), X-ray diffraction (XRD) and vibrating sample magnetometer (VSM). The coercivity of Pr3+ substituted strontium hexaferrite increases at first and then remarkably decreases to 1985.92 Oe at x = 0.5. The value of saturation magnetization (σs) and residual magnetization (σr) relates to the content of α-Fe2O3 phase. With the increasing of Pr3+ doping, the coercivity is improved by 24.7% at x = 0.25 without any significant deterioration in σs and σr. But the substitution of Dy3+ causes a sharply decrease in σs and σr, and the coercivity decreases from 3282.4 Oe to 1410.8 Oe for x = 0 and x = 0.25, respectively. The maximum coercivity (6717.0 Oe), the minimum σs (28.846 emu/g) and σr (15.215 emu/g) are received at x = 0.5 for Dy3+ doping, which could be attributed to the highest content of α-Fe2O3 phase and the smaller grain size of SrFe12O19 phase caused by the simultaneous formation of DyFeO3 and hexaferrite phases.