Crystal structure and magnetic properties of Ti-doped Bi0.84La0.16FeO3 at morphotropic phase boundary

Highlights: • Crystal structure of (La,Ti)-codoped BiFeO₃ at morphotropic phase boundary. • Magnetic properties are strongly dependent on the phase ratio of two crystal structures. • Magnetic interactions at the phase boundary were explained. • The vertical hysteresis shift (exchange bias) is related to the pinned spin at the phase boundary. We have studied the crystal structure and magnetic properties of Bi_0.84La_0.16Fe_1-xTi_xO₃ (x = 0.02–0.1) at the morphotropic phase boundary of R3c, Imma, and Pbam phases. The results of Rietveld-refined X-ray diffraction patterns reveal the existence of multi-phase structures, including R3c + Imma for x = 0.02–0.06 and Imma + Pbam for x = 0.08–0.1. The studies of Raman scattering spectra indicate a structural transformation through the disappearance of typical R3c modes. This strongly influences the magnetic properties that are dependent on the crystalline phase ratio. In particular, the magnetic coercivity of x = 0.04–0.06 drastically changes when the Imma phase is dominant. A mechanism of magnetic interactions occurring at the phase boundary is proposed to explain the features of magnetic hysteresis loops of the compounds.