Elasticity of ferroic and multiferroic materials: a new UK facility for Resonant Ultrasound Spectroscopy with applied magnetic field up to 14 Teslas

This project falls in the field of materials physics and contains two parts. In the initial phase, a new instrument will be built to measure the elastic stiffness of small samples, down to ~1mm^3. The instrument will be based on the principle of Resonant Ultrasound Spectroscopy (RUS) in which a single crystal or polycrystalline sample is caused to vibrate at frequencies close to 1 MHz. In exactly the same manner as a tuning fork or a bell, the vibration frequencies depend on the elastic stiffness of the material and the shape of the object. If the object contains a defect, analogous say to a crack in a bell, some of the vibration energy is dissipated and the resonances are broadened. Resonances of the sample can be measured at low temperatures and at high temperatures so that the elastic properties of an object of known shape can be determined simultaneously with any energy dissipation which occurs within it. These properties are particularly sensitive to changes in crystal structure which might be associated with the development of electric or magnetic dipoles. The new instrument will have the special addition of a strong magnet so that the properties of materials belonging to the topical classes of "ferroic" and "multiferroic" phases can be investigated as functions of both temperature and magnetic field strength. As such it will provide a unique and medium/long term contribution to the science infrastructure of the UK.The second part of the project involves implementation of the new RUS instrument in a series of collaborative studies of materials which develop properties that are potentially important for application in commercial devices involving, for example, superconductors, spintronics and magnetoelectric memories. The principles underpinning the development of these properties are (a) that they arise from subtle changes in crystal structure and/or electronic structure, (b) that they are strongly dependent on temperature and magnetic field strength, (c) that they are associated with changes in strain state and, hence, with large changes in the elastic constants, (d) that they are almost invariably associated with the development of specific types of defects, such as transformation twin walls, which cause the materials to become heterogeneous on a submicroscopic length scale and (e) that such defects have their own structural, electric and magnetic properties. Particular advantage will be taken of the fact that the RUS method provides a highly sensitive method for measuring the extent to which transformation-related defects are mobile in response to an externally applied field. In addition, the new instrument will allow non-destructive testing of mm-sized electronic devices which depend on components that are sensitive to magnetic fields, and the possibility of measuring elastic properties of nanomaterials.

Research into the unusual and highly variable elastic and magnetic properties associated with structural, ferroelectric, magnetic and electronic phase transitions in minerals and technological materials is a specialized field. The specific experimental techniques to be developed and employed in the proposed research are not available in industry and the new RUS instrument will be a unique addition to UK infrastructure for high level research in materials physics. Its application will be to scientific problems that are of immediate relevance to scientists currently working on colossal magnetoresistance materials, multiferroic phases with phase transitions, multiferroic relaxors, pnictide superconductors and quantum ferroelectrics. Outputs from the work will firstly be in the standard form of timely publications in leading scientific journals and presentations at international meetings. An additional feature of the project, however, is that it involves close collaboration with separate research groups in the UK, Spain and Australia. Such collaboration inevitably generates added value because of the transfer of ideas and skills which necessarily accompanies interactions between scientists with quite different backgrounds and operating in different fields (in this case, Earth Sciences, Materials Science, Physics and Chemistry). A broader common theme is the pervasive influence of phase transitions on potential device materials more generally. This theme carries over, also, to real device applications. A specific impact activity of the proposed project is to organize one day meetings in Cambridge amongst all local scientists whose interests fall within this broader theme, so allowing immediate transfer from fundamental science to potential applications. The first meeting of this type in 2010 involved 65 participants and immediately led to some of the collaborative ventures set out here. Two further such meetings are proposed, with emphasis on getting research students and post-docs in 5 different departments (including Engineering) to present their work, and with the explicit intention of giving them well structured opportunities for networking between themselves and with senior academics in different fields.The PI has a background in basic science, but some of the collaborators also have close contacts with industry. It is certain that some of the materials to be investigated or, at least, the properties that they display, will be used in applications such as spintronics and multiferroic memories. For example, J.F.Scott has a well established record of transferring the science of ferroelectrics into the multi-million dollar field of non-volatile random access memory. His participation in projects on pure and doped BiFeO3 and on multiferroic relaxors will ensure that the new insights into strain coupling mechanisms which RUS can provide are transferred into the domain of device development. The timescale over which this will occur is not clear but the intense activity around the world in this field is a clear indicator that commercial applications are expected to be in the short/medium term. The existing and new RUS facilities will also be made available for collaborative projects in other areas. Notably, this has already led to a joint project with members of the University Technology Centre funded by Rolls Royce in Materials Science which has been set up to develop new high temperature Ni-based superalloys. The PDRA employed to undertake this project will have a unique experience of applying specialized techniques to a range of materials where there is both scientific and commercial interest. He/she will also benefit from the wide interactions which will necessarily accrue due to the collaborative nature of the work, and will be well placed to continue a career in academia or industry.