Self-assembled multiferroic perovskite–spinel nanocomposite thin films: epitaxial growth, templating and integration on silicon

Abstract

This review describes recent progress in the growth and properties of self-assembled multiferroic perovskite–spinel nanocomposite thin films, in particular, BiFeO₃–CoFe₂O₄, and their integration on silicon or pre-patterned substrates. Vertically aligned nanocomposite thin films, in which ferromagnetic spinel CoFe₂O₄ nanopillars grow in a ferroelectric perovskite BiFeO₃ matrix, have been investigated for applications such as next generation memory devices. The strain transfer between the two oxide phases at the vertical interface enables cross-coupling of the properties, i.e. a magnetic (electric) field can modify the polarization (magnetization) state, making the nanocomposite a two-phase magnetoelectric multiferroic. The ability to grow high quality thin film nanocomposites and the control of their properties through epitaxial strain transfer are prerequisites for their incorporation into practical devices. Most work has been carried out on perovskite substrates using pulsed laser deposition, and integration on semiconductor-compatible substrates using scalable deposition processes presents a challenge. This review focuses on the epitaxial integration of BiFeO₃–CoFe₂O₄ nanocomposite thin films using sputter deposition on silicon substrates, and discusses recent work on the formation of highly ordered nanocomposites using various template patterning methods. This robust, scalable route for large-area fabrication of multifunctional oxide nanocomposites using sputtering brings the exciting prospects offered by these materials closer towards technological realization.