We report on the coupling between ferroelectric and magnetic order parameters in a nanostructured BaTiO3-CoFe2O4 ferroelectromagnet. This facilitates the interconversion of energies stored in electric and magnetic fields and plays an important role in many devices, including transducers, field sensors, etc. Such nanostructures were deposited on single-crystal SrTiO3 (001) substrates by pulsed laser deposition from a single Ba-Ti-Co-Fe-oxide target. The films are epitaxial in-plane as well as out-of-plane with self-assembled hexagonal arrays of CoFe2O4 nanopillars embedded in a BaTiO3 matrix. The CoFe2O4 nanopillars have uniform size and average spacing of 20 to 30 nanometers. Temperature-dependent magnetic measurements illustrate the coupling between the two order parameters, which is manifested as a change in magnetization at the ferroelectric Curie temperature. Thermodynamic analyses show that the magnetoelectric coupling in such a nanostructure can be understood on the basis of the strong elastic interactions between the two phases.

We present direct evidence for room-temperature magnetization reversal induced by an electric field in epitaxial ferroelectric BiFeO3-ferrimagnetic CoFe2O4 columnar nanostructures. Piezoelectric force microscopy and magnetic force microscopy were used to locally image the coupled piezoelectric-magnetic switching. Quantitative analyses give a perpendicular magnetoelectric susceptibility of approximately 1.0 x 10(-2) G cm/V. The observed effect is due to the strong elastic coupling between the two ferric constituents as the result of the three-dimensional heteroepitaxy.

We have grown BiFeO3 thin films on SrRuO3∕SrTiO3 and SrRuO3∕SrTiO3∕Si using liquid delivery metalorganic chemical vapor deposition. Epitaxial BiFeO3 films were successfully prepared through the systematic control of the chemical reaction and deposition process. We found that the film composition and phase equilibrium are sensitive to the Bi:Fe ratio in the precursor. Fe-rich mixtures show the existence of α-Fe2O3, while Bi-rich mixtures show the presence of β-Bi2O3 as a second phase at the surface. In the optimized films, we were able to obtain an epitaxial single perovskite phase thin film. Electrical measurements using both quasistatic hysteresis and pulsed polarization measurements confirm the existence of ferroelectricity with a switched polarization of 110–120μC∕cm2, ΔP(=P*−P̂). Out-of plane piezoelectric (d33) measurements using an atomic force microscope yield a value of 50–60pm∕V.

Arrays of perpendicular ferromagnetic nanowires have recently attracted considerable interest for their potential use in many areas of advanced nanotechnology. We report a simple approach to create self-assembled nanowires of alpha-Fe through the decomposition of a suitably chosen perovskite. We illustrate the principle behind this approach using the reaction 2La(0.5)Sr(0.5)FeO(3) --> LaSrFeO(4) + Fe + O(2) that occurs during the deposition of La(0.5)Sr(0.5)FeO(3) under reducing conditions. This leads to the spontaneous formation of an array of single-crystalline alpha-Fe nanowires embedded in LaSrFeO(4) matrix, which grow perpendicular to the substrate and span the entire film thickness. The diameter and spacing of the nanowires are controlled directly by deposition temperature. The nanowires show uniaxial anisotropy normal to the film plane and magnetization close to that of bulk alpha-Fe. The high magnetization and sizable coercivity of the nanowires make them desirable for high-density data storage and other magnetic-device applications.