Effect of structural phase transition on magnetic and optical properties of co-substituted bismuth ferrite

Beside the disappearance of characteristics superlattice reflections for R3c space group as (1 1 3) at 2θ=37.8°, the typical reflections of Pbnm space group as (1 1 1) at 2θ=25.42° as well as their new superlattice reflections such as (0 2 1), (0 2 3) and (2 2 1) at 2θ=34.14°, 47.69° and 47.82° which are characteristic of the antiparallel cation displacements has appeared for 7.5% of co-substitution (Eu in Bi site and Mn in Fe site) in BiFeO3. Morphological phase boundary has been observed around 7.5% of co-substitution which have enhanced remnant magnetization about 20 times that of pure one and it could be due to the suppression of cycloid spin structure and spin canting at the surface of nanocrystallites. Further increase in co-substitution percentage (>7.5%) leads to the reduction of remnant magnetization due to the appearance of collinear antiferromagnetic ordering in the Pbnm space group which becomes significant for higher co-substitution percentage. The analysis of diffuse reflectance spectra which shows the point group symmetry breaking from Oh to C3v supports the modification in local FeO6 environment and structural transition.