Molarity dependent oscillatory structural and magnetic behavior of phase pure BiFeO3 thin films: Sol–gel approach

Abstract

An extensive study of oscillatory response of structural and magnetic behavior of phase pure bismuth iron oxide (BiFeO3) thin films is reported in the present study. Sol-gel method is used to synthesize BiFeO3 sols at room temperature. Molarity, being an important parameter in chemical synthesis, is varied (0.25 M, 0.3 M, 0.35 M, 0.4 M, 0.45 M, 0.5 M, 0.55 M and 0.6 M) and the effect is investigated in detail. Spin coated thin films are structurally studied by X-ray diffraction (XRD) method. Films prepared using 0.35 M and 0.5 M sols confirm the formation of pure hexagonal phase of perovskite structure with R3c (161) space group. Strengthening of BiFeO3 phase is observed after magnetic field annealing (MFA) of samples at 300 °C for 2 hours. Mixed bismuth iron oxide phases (i.e. bismuth rich or deficient) are observed in thin films prepared using rest of the sols. Preferred orientation oscillates between (122) and (315) as a function of the appearance of pure and mixed BiFeO3 phases, respectively. Refined XRD parameters show -ive tilt in bond angle (i.e. ~ -7.148°) in the films with mixed bismuth iron oxide phases. Whereas, +ive tilt (i.e. 2.55° and 4.49°) in bond angles are responsible for the appearance of phase pure bismuth iron oxide phase at 0.35 M and 0.5 M sol concentration. Room temperature ferromagnetic behavior with high value of saturation magnetization is observed for films prepared using 0.35 M (109 emu/cm3) and 0.5 M (135 emu/cm3) sols. Law of approach to saturation magnetization is used to calculate magneto crystalline anisotropy.