Origin of enhanced magnetization in (La,Co) codoped BiFeO3 at the morphotropic phase boundary

In this work, we studied the effect of Co doping on the crystal structure and magnetic properties of Bi0.84La0.36FeO3 polycrystalline ceramics. The analysis of X-ray diffraction patterns (XRD) demonstrates the coexistence of the R3c rhombohedral and Imma orthorhombic structures, along with small Bi25FeO40 and CoFe2O4 parasitic impurities in the samples. The study of phonon vibration with different excitation wavelengths identifies an individual contribution of two structures on the Raman spectra. Scanning electron micrographs identify small and large grains in the Imma and R3c phases, respectively. The magnetic impurity strongly impacted the magnetic properties of the compounds, while La and Co substitution for BiFeO3 at the polymorphs induces the phase boundary ferromagnetism. The enhancement of magnetization mainly originates from magnetic impurity and phase boundary ferromagnetism. The variation in magnetization confirms a formation of phase boundary spins, and distinguishes the individual contributions of the coexisting phases and CoFe2O4 on the magnetic properties of the compounds.