Fabrication of the BiFeO$_3$/Sr$_{0.6}$Ba$_{0.4}$Nb$_2$O$_6$/SrRuO$_3$/MgO(001) heterostructure, as well as features of its crystal structure, surface morphology, and physical properties

Studies of the crystal structure, surface nanostructure, and properties of the BiFeO$_3$/Sr$_{0.6}$Ba$_{0.4}$Nb$_2$O$_6$/SrRuO$_3$/MgO(001) heterostructure were carried out. Nanosized SrRuO$_3$(25 nm), Sr$_{0.6}$Ba$_{0.4}$Nb$_2$O$_6$(100 nm), and BiFeO$_3$(100 nm) films were deposited sequentially on a MgO(001) substrate by RF-cathode sputtering in an oxygen atmosphere. It has been established that there are no impurity phases in the fabricated heterostructure, all layers are grown heteroepitaxially, and the deformation of the unit cell in the upper BiFeO$_3$ layer was 0.28%. It has been shown that during the deposition of each subsequent layer in the series of MgO(001) $\to$ SRO $\to$ SBN60 $\to$ BFO, the surface roughness of the upper film increases from 0.292 nm to 2.977 nm, but the maximum lateral crystallite size is observed for SBN60. The revealed regularities and features in the analysis of the magnetic and ferroelectric properties of the heterostructure obtained by magnetic force microscopy and atomic force microscopy are discussed.