Improving of ferroelectric and magnetic properties of Bi5Ti3FeO15 multiferroic materials with Y3+ and Co2+ partial substitution

Abstract

The search for multiferroic materials combining electric and magnetic properties in a single phase has attracted a lot of attention in the perspective of future magnetoelectronic devices. A handful of single phase multiferroics have been discovered so far, and most of them are not suitable for practical applications at present, either because the room temperature polarization/magnetization is too small or their mutual coupling is too weak. One of the most important single-phase multiferroic material with Aurivillius structure is Bi5Ti3FeO15 (BFT) which generally yields a magnetoelectric coupling above room temperature. The main lack of this material is high electrical conductivity and hence the lower ferro-electromagnetic properties. Since BFT has the capability to host ions of different size, multiferroic properties could be improved by using dopants or ionic substitutions on different A and B-sites of the structure. To this respect, Co2+ and Y3+ doped BFT were prepared by the solid state reaction method according to formulas: Bi1-xYxTi3FeO15 (x=0.1, 0.2, 0.3) and BiTi3Fe1-yCoyO15(y=0.1, 0.3, 0.5). Slightly improve of ferroelectric properties was noticed with 0.3 mol% of Co while replacement of Bi3+ with Y3+ causes a reduction in orbital hybridization between Bi 6sand O 2s/2porbitals leading to a decrease in electric polarization as a vector sum of all dipole moments. Magnetic measurements confirm the antiferromagnetic nature of pure and Y doped ceramics while Co-doped samples exhibit a typical ferromagnetic loop reveals the existence of FM interactions in these samples. The largest Mr value appears in samples doped with 3 mol% of Co (Mr of 0.084 emu/g and Hc of 287 Oe). Raman spectroscopy confirmed that Y prefer to replace Bi ions in the pseudo-perovkite layers while Co ions enter into the lattice and occupy the Fe site inside of oxygen octahedral.