Abstract
BiFeO3 (BFO) films on highly oriented pyrolytic graphite (HOPG) substrate were obtained by the atomic layer deposition (ALD) method. The oxidation of HOPG leads to the formation of bubble regions creating defective regions with active centers. Chemisorption occurs at these active sites in ALD. Additionally, carbon interacts with ozone and releases carbon oxides (CO, CO2). Further annealing during the in situ XPS process up to a temperature of 923 K showed a redox reaction and the formation of oxygen vacancies (Vo) in the BFO crystal lattice. Bubble delamination creates flakes of BiFeO3-x/rGO heterostructures. Magnetic measurements (M–H) showed ferromagnetism (FM) at room temperature Ms ~ 120 emu/cm3. The contribution to magnetization is influenced by the factor of charge redistribution on Vo causing the distortion of the lattice as well as by the superstructure formed at the boundary of two phases, which causes strong hybridization due to the superexchange interaction of the BFO film with the FM sublattice of the interface region. The development of a method for obtaining multiferroic structures with high FM values (at room temperature) is promising for magnetically controlled applications.
Highlights
The demand for the use of multiferroics in various fields and products of nanoelectronics has been growing steadily
BiFeO3 (BFO) films on highly oriented pyrolytic graphite (HOPG) substrate were obtained by the atomic layer deposition (ALD) method
We found that heat treatment in high vacuum promotes the formation of a BFO/rGO heterostructure and delaminates the near-surface HOPG layers creating local defects with the release of carbon oxides (CO, CO2)
Summary
The demand for the use of multiferroics in various fields and products of nanoelectronics has been growing steadily. Hyun Wook Shin and Jong Yeog Son [19] presented the Graphene/BFO/HOPG capacitor structure obtained by pulsed laser deposition and showed multiferroic properties, namely, ferroelectricity and ferromagnetism. To enhance the magnetic properties, BFO is doped with Ho and Mn atoms, such films were obtained by the traditional sol–gel method, where the maximum magnetization reached values Ms ~ 60 emu/cm3 [36] This enhancement was explained by lattice distortions caused by the difference in ion sizes between the doping agent and the matrix, the emergence of new exchange interactions, and the inhibition of the antiferromagnetic spiral modulated spin structure. We found that heat treatment in high vacuum promotes the formation of a BFO/rGO heterostructure and delaminates the near-surface HOPG layers creating local defects with the release of carbon oxides (CO, CO2). An additional contribution of the superstructure at the film–substrate interface to the FM of the resulting BFO multiferroic is discussed
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