Time Resolved Imaging of Multifunctional Materials in Three Dimensions (TRIMM3D)

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Multifunctional ferroic materials are materials that simultaneously exhibit more than one ferroic property including ferromagnetism, ferroelectricity, ferroelasticity or ferrotoroidicity. Ferroic materials that exhibit more than one property are of great interest because the different properties may work together in different ways and lead to exciting new potential applications, if we could understand this better. For example, the coupling between magnetic and ferroelectric ordering can be utilised to develop low power magnetoelectronic devices (such as non-volatile magnetic computer memory) where the spin polarised transport of electrons can be used to flip magnetic memory bits. As a result there is a vibrant effort to understand the underlying mechanisms at work in bulk and thin film materials. Many of the multiferroic materials that I am interested in have a certain structure called a perovskite crystal structure. Before multiferroic perovskite materials can find significant utility in a device setting, a clear understanding of the materials behaviour at the nanoscale is needed. Often the role of crystal defects and other topological structures remains unclear as (to date) no reliable means exists to image in three-dimensions and observe such effects in real-time. Moreover, if the crystal isn't grown carefully, it can easily grow in a different structure that doesn't display the properties that we want to investigate.To better understand these materials I will use a technique called Bragg coherent X-ray diffractive imaging (BCXDI) without lenses. This is a form of x-ray microscopy that can permit high resolution imaging where the use of conventional optics is not feasible. The ability that BCXDI has to directly image time varying structural properties of materials in three-dimensions at the surface and in the bulk can greatly increase our understanding of how novel phases emerge and influence the material properties. The application of BCXDI to the study of multifunctional materials will enable a wide range of next generation technologies that otherwise are inaccessible due to an incomplete understanding of their properties. A prominent example prototypical system is bismuth ferrite which exhibits a large reversible crystal deformation (up to 0.5%) in response to optical excitation. It remains unclear exactly how optically generated electron-hole pairs in bismuth ferrite can cause a large lattice deformation which appears to propagate faster than the speed of sound in the material. Moreover the exact role of electron-hole pairs and the propagation vector of the distortion remains unclear. Utilising time-resolved BCXDI will enable direct visualisation of the lattice distortion in three-dimensions from which the atomic displacements can be inferred and contrasted with model predictions. This project will focus on imaging time-varying structural phenomena in a wide range of ordered multifunctional matrials by employing a novel deterministic form of BCXDI to obtain three-dimensional images. The application of deterministic BCXDI to the study of dynamic structural phenomena will provide a novel and robust means to directly image in three-dimensions non-equilibrium dynamics of the material undergoing a symmetry breaking structural transformation. Knowledge of the atomic displacements from equilibrium is obtained with sub-angstrom sensitivity and will greatly aid our understanding of the kinetics of dynamic phenomena that are central to the development of next generation materials and devices. This research proposal will be carried out in collaboration with Prof. Steve Collins, Diamond Light Source, Oxfordshire and Prof. Hans Fangohr, European Xray Free Electron Laser (E-XFEL) Facility in Hamburg.