Soft chemical routes to novel magnetoelectric materials

Lead Research Organisation: University of Oxford
Department Name: OxICFM CDT

Abstract

More and more, we are seeing that combining useful and fascinating phenomena into a single, multifunctional material is driving the development of new advanced materials. Most interesting are properties that interact mutually to result in cooperative effects. Magnetoelectric multiferroic materials are simultaneously ferromagnetic (containing lined up magnetic dipoles of north and south poles) and ferroelectric (containing lined up electric dipoles made of positive and negative charges), meaning that they display a spontaneous magnetisation that can be reoriented by an applied magnetic field, and a spontaneous electric polarisation that can be reoriented by an applied electric field, within a single phase.
Besides scientific interest in their fundamental physical properties, novel multiferroic materials not only offer all the potential applications of ferromagnetic and ferroelectric materials, but also open the door to a range of other multifunctional applications. The most exciting of these is the ability to control the magnetic properties of a phase with an electric field, making technology which relies of magnetism more energy efficient. However, these materials have proven to be extremely challenging to synthesise, since the presence of one constituent ferroic property often precludes the onset of the other. As such, research has focussed on developing new approaches that can be used to design these materials.
The perovskite phase is an ideal system within which to study these properties, as the structure is flexible and can accommodate a range of elements. The cubic perovskite has the general formula ABX3, where the A-site ion occupies the corners of the lattice and the B-site ion occupies the centre of an octahedron, whilst six X-ions are positioned on the vertices. Recently, considerable effort has been made to exploit the cooperative rotations and tilts of the BX6 octahedra since they are ubiquitous in the perovskite structure and can be controlled through careful chemical substitution. Most importantly, the octahedral rotations couple strongly to the magnetic and electronic properties of the material. A novel mechanism, coined the 'trilinear coupling mechanism', which takes advantage of the rotation patterns of layered perovskites, has been investigated as a strategy to induce ferroelectricity in such materials.
The overarching aim of this project is to synthesise novel magnetoelectric multiferroic perovskite materials, exploiting the trilinear coupling mechanism to induce ferroelectricity and soft synthetic routes to obtain phases that would not be accessible using traditional ceramic solid-state methods, such as extremely high temperatures. More specifically, a series of distorted layered fluoride-perovskite phases will be synthesised. Existing literature on layered fluoride phases is scarce, since their oxide analogues tend to be more stable and as such, easier to synthesise. Because of this, novel solution-based synthetic methods will be employed in combination with solid-state techniques to obtain new phases. These materials will be studied using very high intensity x-rays and neutrons, which are necessary as the octahedral rotations and tilts being studied are small compared to the rest of the material.
This project falls within the EPSRC Physical sciences research area, and is co-supervised by Professor Stephen Blundell from the Department of Physics, Oxford University.

Publications

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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/S023828/1 01/04/2019 30/09/2027
2329318 Studentship EP/S023828/1 01/10/2019 30/09/2023 Rachel Conway