Effects of Dy and Co co-substitution on the magnetic properties and TC of BiFeO3 ceramics

Multiferroic Bi0.95Dy0.05Fe1-xCoxO3 (x=0, 0.05, 0.1, 0.15) ceramics were prepared by rapid liquid phase sintering method. We studied the effect of (Dy+Co) doping on the structure, electrical and ferromagnetism properties of BiFeO3 ceramics. The structure and morphology of BiFeO3 ceramics were characterized by X-ray diffraction (XRD) and scanning electron microscopey (SEM). The results showed that all the peaks for Bi0.95Dy0.05Fe1-xCoxO3 samples can be indexed based on the crystal structure of pure BiFeO3. And XRD analysis revealed a phase transition in (Dy+Co) co-doped BiFeO3 when x was larger than 0.1 and grain sizes changed from 1 to 5 μm. Magnetic hysteresis loops were clearly observed in co-substituted specimens and magnetization was greatly improved. Magnetic measurements showed that all samples possess strong ferromagnetism at room temperature expect BiFeO3 and Bi0.95Dy0.05FeO3, which are weakly ferromagnetic. The M'rs, of Bi0.95Dy0.05Fe1-xCoxO3 with x=0.05, 0.01 and 0.15 are 0.43, 0.489, 0.973 emu/g and the M'rs of them are 0.77, 1.65, 3.08 emu/g, respectively. The magnetic moment of BiFeO3 and B0.95Dy0.05Fe1-xCoxO3 ceramics varies with temperature from 300 to 900 K at an applied field of 5 kOe. It shows that the TN of BiFeO3 from 644 to 648 K with different content of Dy3+ can be changed by crystal structures and exchanges between Dy3+-Fe3+. The phase transition temperature of Bi0.95Dy0.05Fe1-xCoxO3 shifted to lower temperatures from 870 K to 780 K demonstrate that Co3+ doping causes a drop of TC as compared with BiFeO3. The change of TC of Bi0.95Dy0.05Fe1-xCoxO3 depends mainly on the Fe-O-Fe super-exchange strength and the relative stability of magnetic structure.