Multiferroic Nanostructured Thin Films

Lead Research Organisation: Imperial College London
Department Name: Materials

Abstract

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.

Publications

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Description Multi-functional materials can respond to more than one external stimulus. Here we studied a multiferroic system which couples two or more switchable states such as polarization and magnetisation. Multiferroic materials span a rich diversity of phenomena and applications. They have striking unique features such as cross-coupling of electro-magnetic, electro-elasto and electro-optic properties.

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 made 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.

There is a tremendous need for further research bridging all the way from atomic defects, nanoscale structure of domain walls, epitaxial stress and strain, to their order of magnitude impact on macroscale properties.



The ultimate aim of this proposal was to develop

(i) lead-free piezoelectric thin films and

(ii) periodically nanostructured multiferroic thin-films with switchable magnetic domains



In the course of this development several other goals were achieved:

- understanding the relation between the crystal chemistry and piezo and dielectric properties of Ag(Nb,Ta)O3

- understanding of the influence of the strain and quantum-size effect on the magnetic properties of CoFe2O4 thin films

- development of a PLD technique for the production of the thin-film with an artificial crystallographic superstructure

- use of the active substrate concept for elimination of the clamping effect between the substrate and the thin film
Exploitation Route The potential uses for effective multiferroic materials are substantial and particularly in the area of information technmology No exploitation routes currently identified
Sectors Aerospace/ Defence and Marine

Digital/Communication/Information Technologies (including Software)

Electronics

Energy