Rhenium substitution effects on the structural, morphological and magnetic properties of bismuth ferrite BiFe_(1-x)Re_xO₃

In order to fully realize room temperature multiferroicity, a release of remnant magnetization in the BiFeO3 (BFO) system is still needed. Herein, we describe novel Re -substituted BiFe1-xRexO3 compounds that were synthesized using an aqueous sol-gel procedure when ethylene glycol was used as a complexing agent. Rhenium substitution was used to disrupt the modulated magnetic structure due to its aliovalent nature and maintain electroneutrality in case of Bi evaporation. Obtained compounds were investigated using X-ray powder diffraction (XRD) analysis coupled with Rietveld refinement, Raman spectroscopy and X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), as well as magnetometry measurements. The obtained data revealed that only tiny amounts of Re (<= 0.75 %) can be introduced instead of Fe ions while maintaining a single-phase structure. Larger inclusions lead to the formation of two impurity phases with Pbam and I2(1)3 space groups. However, the typical R3c bismuth ferrite crystal structure remained dominant. SEM analysis indicated that the inclusion of Re ions into the crystal structure caused an increase in average particle size. XPS analysis confirmed the designed chemical compositions of the samples as well as the small amount of Fe2+, which is formed to compensate for the Re ions in the 6+ and 7+ states. Magnetometry measurements revealed that even sub 1 % of Re substitution led to a presence of non -zero remnant magnetization, which reaches 0.0449 Am(2)kg(-1) at room temperature in the compound with x = 0.0075.