Enhanced bending-tuned magnetic properties in epitaxial cobalt ferrite nanopillar arrays on flexible substrates

Abstract

Herein, large-scale epitaxial (111) CoFe₂O₄ nanopillar arrays with an average nanopillar diameter of ∼40–60 nm and thicknesses of 26–700 nm have been obtained on flexible fluorophlogopite substrates by chemically etching the vertically aligned self-assembled CoFe₂O₄:MgO nanocomposite thin films. The chemical etching process has not affected the crystalline quality of the CoFe₂O₄ phase, but results in volume shrinkage through the removal of the surrounding MgO phase. Compared with the planar CoFe₂O₄ films, the nanopillar arrays show sharply declined coercivity and enhanced saturation magnetization. Even the thinnest nanoisland-shaped arrays (∼26 nm) retain a relatively high saturation magnetization (∼90 emu cc⁻¹), nonzero coercivity (∼250 Oe), and remanence (∼30 emu cc⁻¹), which are promising for the requirements of weak ferromagnetism in flexible devices. With an increase in the bending radius, a strong and monotonous increase in saturation/remanent magnetization has been found in the nanopillar arrays. This reveals that the bending-induced shape anisotropy as well as the intrinsic magnetocrystalline anisotropy mainly dominate the tunable magnetic properties in the CoFe₂O₄ nanopillar arrays. With strong bending, the increment of remanent magnetization in the nanopillar arrays can be as high as 98%, exhibiting the huge potential of these nanopillar arrays in future applications such as in bending sensors and related devices.