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Multiferroic StTiO3/BiFeO3 Superlattice:Theory and Experiment

A. Roy, A. Garg, R. Prasad, S. Auluck
Indian Institute of Technology Kanpur, IN

Keywords: multiferroic, SrTiO3, BiFeO3, superlattice


Materials designing using the concept of artificial layered structures has opened up a new vista in process engineering owing to the possibility of evolving unusual and novel functional properties which are often not found in the respective bulk systems. With this motivation, we performed density functional theory based calculations for structural, electrical and magnetic properties of SrTiO3/ BiFeO3 (STO/BFO) multilayer. Our calculations suggest that the ground state structure comprises of tetragonal P4mm symmetry with G-type antiferromagnetic spin structure having in-plane lattice parameters, a = b = 3.8856 Å. Further, electronic band structure and density of states, calculated based on the ground state structure, showed the material to have a band gap ~ 1.69 eV. Magnetic moment per Fe site was found to be ~ 4.09 Bohr magneton. Spontaneous polarization, calculated using Berry phase method showed large polarization (~ 60 micro C/cm2) in the out of plane direction. Ti and O ions were identified as the chief contributors toward polarization. This was found to be in contrast with the case of multiferroic BiFeO3 where Bi and O contribute most to the spontaneous polarization. In order to validate our calculated results, we grew alternate layers of SrTiO3 and BiFeO3 on (100) oriented 0.1 % Nb doped SrTiO3 substrates using pulsed laser deposition technique. Deposited films were subsequently characterized for structural, ferroelectric and magnetic properties as a function of layer thickness and number of layers. Experimentally determined band gap was found to be larger than that of theoretical prediction but the spontaneous polarization was in reasonable agreement with the theoretical value.
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