Selectable Spontaneous Polarization Direction and Magnetic Anisotropy in BiFeO3−CoFe2O4 Epitaxial Nanostructures

We demonstrate that epitaxial strain engineering is an efficient method to manipulate the ferromagnetic and ferroelectric properties in BiFeO3−CoFe2O4 columnar nanocomposites. On one hand, the magnetic anisotropy of CoFe2O4 is totally tunable from parallel to perpendicular controlling the CoFe2O4 strain with proper combinations of substrate and ferroelectric phase. On the other hand, the selection of the used substrate allows the growth of the rhombohedral bulk phase of BiFeO3 or the metastable nearly tetragonal one, which implies a rotation of the ferroelectric polar axis from [111] to close to the [001] direction. Remarkably, epitaxy is preserved and interfaces are semicoherent even when lattice mismatch is above 10%. The broad range of sustainable mismatch suggests new opportunities to assemble epitaxial nanostructures combining highly dissimilar materials with distinct functionalities.