100-nm-sized magnetic domain reversal by the magneto-electric effect in self-assembled BiFeO(3)/CoFe(2)O(4) bilayer films

A (001)-epitaxial-BiFeO(3)/CoFe(2)O(4) bilayer was grown by self-assembly on SrTiO(3) (100) substrates by just coating a mixture precursor solution. The thickness ratio of the bilayer could be controlled by adjusting the composition ratio. For example, a BiFeO(x):CoFe(2)O(x) = 4:1 (namely Bi(4)CoFe(6)O(x)) mixture solution could make a total thickness of 110nm divided into 85-nm-thick BiFeO(3) and 25-nm-thick CoFe(2)O(4). Self-assembly of the bilayer occurred because the perovskite BiFeO(3) better matched the lattice constant (misfit approximately 1%) and crystal symmetry of the perovskite SrTiO(3) than the spinel CoFe(2)O(4) (misfit approximately 7%). The magnetic domains of the hard magnet CoFe(2)O(4) were switched by the polarization change of BiFeO(3) due to an applied vertical voltage, and the switched magnetic domain size was approximately 100nm in diameter. These results suggest that self-assembled BiFeO(3)/CoFe(2)O(4) bilayers are interesting in voltage driven nonvolatile memory with a low manufacturing cost.