Strain-induced structural phase transition, ferromagnetic and optical properties of Bi_1-xTb_xFeO₃ thin films

In this paper, we report on the structural phase transition, surface morphologies, ferromagnetic and optical properties that have been observed in Bi_1-xTb_xFeO₃ (BTFO) thin films with (x = 0, 0.03, 0.06 and 0.09). X-ray diffraction (XRD) indicated that all the films have a single phase with rhombohedral structure and exhibit gradual transition behavior to pseudo-tetragonal structure with the increase of x, the strain values were estimated to be 0.1-0.8, depending on composition. A possible mechanism, strain-induced structural phase transition, is discussed. The micro-Raman spectroscopy analysis was in good agreement with structural phase transition verified by the XRD patterns. Moreover, with an increase in Tb³⁺ ions from x = 0-0.06, the saturation magnetization of the BTFO thin films shows a linear increase, which is mainly due to the Tb³⁺ ions. However, a sharp increase emerges with x from 0.06 to 0.09, the phase transition mainly dominates the higher ferromagnetism in BTFO films. Moreover, BTFO films with x > 0 exhibit a lower band-gap than that with x = 0, originating from local rhombohedral to pseudo-tetragonal structure transition. These results are helpful for a deeper understanding of structural transition, magnetic, and optical properties in perovskite oxides and show the potential roles, which such materials can play in multiferroic applications and solar energy devices.