Ferromagnetism in nitrogen and fluorine substituted BaTiO3
Polycrystalline BaTiO3, BaTi(O,F)3, BaTi(N,O)3, and BaTi(N,O,F)3 powders were synthesized by a solid-state reaction and thermal ammonolysis. By powder X-ray diffraction (XRD) a tetragonal perovskite-type structure with space group P4mm was identified for all samples. Thermogravimetric analysis (TGA) revealed a gradual mass increase for the oxynitride BaTi(N,O)3 and the oxyfluoronitride BaTi(N,O,F)3 due to the nitrogen-oxygen exchange process. UV-visible diffuse reflectance spectra indicated the nitrogen incorporation into the perovskite lattice, and presumably the presence of large amounts of reduced titanium ions in BaTi(N,O,F)3. XANES spectra showed distinctive peak features for BaTi(O,F)3 and BaTi(N,O,F)3. Detailed magnetic property measurements revealed diamagnetism for BaTiO3, but weak ferromagnetism for BaTi(N,O)3 and a ferromagnetic behavior for BaTi(O,F)3 and BaTi(N,O,F)3. Enhanced magnetization of BaTi(N,O,F)3 is attributed to the synergetic effect of increased concentration of both surface/lattice defects and Ti3+.