Multiferroic Nanostructured Thin Films

多铁性材料具有丰富多样的现象和应用。它们具有电磁、电弹性和电光特性交叉耦合等显著特征，从原子缺陷、畴壁的纳米级结构、外延应力和应变，到它们对宏观性能的数量级影响，都需要进一步的研究。挑战在于将铁磁性与铁电性结合起来，然后将铁磁性与铁电性耦合起来。为了实现这一点，我们需要同时室温铁电性和铁磁性。氧化物钙钛矿是一种非凡的材料家族，可以通过掺杂来提供广泛的功能。从局域电子行为到巡回电子行为以及从铁电态到反铁电态的转变是由原子尺度上相互冲突的不稳定性决定的。问题：一个真正的多铁性材料是一个单一的材料，如铋铁氧体，表现出多铁性行为。问题是，所有真正的多铁性材料都没有足够的现象之间的耦合，无法用于器件。当在单一材料中实现时，关键特性会受到损害。解决方案：在这个方案中，我们将分别制作铁电、铁磁和压电材料的薄膜，但在人工超级单体中距离很近。通过这样做，我们可以优化单个材料的关键性能，但在宏观尺度上确保材料之间的耦合，以获得良好的器件性能。

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.