Electron spin resonance studies and improved magnetic properties of Gd substituted BiFeO3 ceramics

Polycrystalline Bi1−xGdxFeO3 (x=0.00–0.15) ceramics were prepared by solid-state reaction method. The samples preserve rhombohedral symmetry for x≤0.10 and coexistence of rhombohedral R3c and orthorhombic Pn21a symmetries for x>0.10. A significant change in the phonon frequencies of A1 modes and line widths in Raman spectra also confirms the structural transition from rhombohedral to orthorhombic for x=0.12 and 0.15. The improved magnetic behaviour indicates weak ferromagnetism in the samples with remnant magnetization (2 Mr) of 0.145 emu/g for x=0.15. An asymmetric shift in the coercive field indicates the presence of exchange bias effect in samples. Electron spin resonance spectra are of the ferromagnetic resonance type at higher dopant concentration and indicate the presence of ferromagnetically coupled clusters in the samples. Optical studies in the spectral range from 1.6–5.2 eV were dominated by one doubly degenerate d–d transition and three charge transfer transitions. The optical band gap decreases from 2.25 to 2.16 eV with increasing Gd substitution due to increased lattice distortion.