The Influence of Annealing Temperature on the Structure and Magnetic Properties of Nanocrystalline BiFeO3 Prepared by Sol–Gel Method

In this work, BiFeO3 powders were synthesized by a sol–gel method. The influence of annealing temperature on the structure and magnetic properties of the samples has been discussed. X-ray diffraction studies showed that the purest phase was formed in the temperature range of 400 °C to 550 °C and the samples annealed at a temperature below 550 °C were of nanocrystalline character. Mössbauer spectroscopy and magnetization measurements were used as complementary methods to investigate the magnetic state of the samples. In particular, the appearance of weak ferromagnetic properties, significant growth of magnetization, and spin-glass-like behavior were observed along with the drop of average grain size. Mössbauer spectra were fitted by the model assuming cycloidal modulation of spins arrangement and properties of the spin cycloid were determined and analyzed. Most importantly, it was proved that the spin cycloid does not disappear even in the case of the samples with a particle size well below the cycloid modulation period λ = 62 nm. Furthermore, the cycloid becomes more anharmonic as the grain size decreases. The possible origination of weak ferromagnetism of the nanocrystalline samples has also been discussed.

Microstructure, XRD and Mössbauer spectroscopy study of Gd doped BiFeO3

The results of fabrication process and characterization of Bi1-xGdxFeO3 (x = 0.05, 0.07, 0.10) ceramics are reported in the paper. The samples were prepared by standard solid state reaction method from the mixture of oxides: Bi2O3, Fe2O3 and Gd2O3. The influence of Gd substitution on the microstructure and density of Bi1-xGdxFeO3 was studied. Phase composition and structure of the obtained samples were investigated by Xray diffraction. It turns out that the Bi1-xGdxFeO3 solid solutions with x = 0.05 and 0.07 crystallize in trigonal structure characteristic of BiFeO3 compound. For the sample with x = 0.1, beside the major trigonal phase, 6% of orthorhombic phase typical for GdFeO3 was detected. Hyperfine interaction parameters were studied by M?ssbauer spectroscopy. M?ssbauer results proved that the spin cycloid characteristic of BiFeO3 compound gradually disappears when substituting Gd3+ ions at the Bi3+ sites.