Multiferroic Nanostructured Thin Films

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Multiferroic materials span a rich diversity of phenomena and applications. They have striking features such as cross-coupling of electro-magnetic, electro-elasto and electro-optic properties and there is a tremendous need for further research bridging all the way from atom defects, nanoscale structure of domain walls, epitaxial stress and strain, to their order of magnitude impact on macroscale properties.The challenge is to combine ferromagnetism with ferroelectricity and then to couple ferromagnetism with ferroelectricity. In order to achieve this we need simultaneous room temperature ferroelectricity and ferromagnetism. Oxide perovskites are a remarkable family of materials that can be doped in order to provide a huge range of functions. Transitions from localised to itinerant electronic behaviour and from ferroelectric to anti FE states are determined by conflicting instabilities on an atomic scale. The Problem: A true multiferroic material is one where a single material, such as bismuth ferrite, exhibits multiferroic behaviour. The problem is that all true multiferroic materials possess insufficient coupling between phenomena to be useful for devices. The key properties are compromised when realised in a single material.The Solution: In this proposal we will make films of e.g. ferroelectric, ferromagnetic and piezoelectric material separately, but in close proximity in an artificial supercell. By doing this we can optimise the key properties of the single material but on a macroscopic scale ensure coupling between the materials to obtain good device performance.