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Cambridge NERC Doctoral Training Partnerships

Graduate Research Opportunities

Lead Supervisor: Richard Harrison, Earth Sciences

Co-Supervisor: Emilie Ringe, Earth Sciences and Charan Kuppili, Canadian Light Source

Brief summary: 
Be a part of the next revolution in magnetic imaging as we develop the first 3D nanomagnetic microscopy method for Fe-bearing samples.
Importance of the area of research concerned: 
The field of nanopaleomagnetism is concerned with the properties, behaviour and applications of natural magnetic nano-structures. This field has been revolutionised over the past decade by the ability to image the magnetic structure of natural samples with nanoscale resolution using methods such as electron holography and X-ray photoemission electron microscopy. However these methods are inherently two-dimensional in nature, whereas natural magnetic nanostructures are inherently three-dimensional. Micromagnetic simulations have revealed the importance of complex 3D states in controlling natural paleomagnetic remanence, yet there is presently no experimental method capable of imaging such states and testing the veracity of our simulations. Donnelly et al. (2017) have demonstrated that it is possible to perform 3D nanomagnetic imaging of Gd using the method of X-ray dichroic ptychotomography. However, natural magnetic materials are generally Fe-based, and therefore there is a pressing need to adapt this method for application to Fe-bearing samples. If successful, this will usher in a new revolution in nanomagnetic imaging of natural materials.
Project summary : 
Ptychography is a synchrotron X-ray imaging technique that reconstructs an image from X-ray diffraction patterns obtained at well known, pre-defined scan points across a sample. Spatial resolutions as high as 5 nm and 17 nm are reported in the soft (energy < 2 keV) and hard (energy > 6.5 keV) X-ray regimes, respectively. Dichroic ptychography combines conventional ptychography with X-ray magnetic circular dichroism (XMCD) to achieve magnetic contrast. Dichroic ptychotomography combines dichroic ptychography with conventional tomography in order to obtain a 3D vectorial magnetisation field. Although this method is well established for hard X-rays tuned to the Gd K-edge, this project will be the first to attempt the method using soft X-ray at the Fe L-edge. If successful, this will open the door to imaging natural magnetic materials in 3D at the nanoscale for the first time.
What will the student do?: 
The student will perform a series of synchrotron X-ray experiments at the Canadian Light Source using a range of natural and synthetic Fe-bearing samples. Samples will be prepared using focussed ion beam milling to create 200 nm needles that are thin enough to transmit soft X-rays at the Fe L-edge. Further characterisation of the samples using existing techniques, such as transmission electron microscopy, electron holography and atom probe tomography will be performed. The student will learn how perform, process and analyse the data, and interpret the results using micromagnetic simulations. The results will be used to inform rock and paleomagnetic theories of samples that go beyond the conventional single domain threshold, i.e. those containing vortex and multi-vortex states.
References - references should provide further reading about the project: 
Donnelly, C., Guizar-Sicairos, M., Scagnoli, V., Gliga, S., Holler, M., Raabe, J., & Heyderman, L. J. (2017). Three-dimensional magnetization structures revealed with X-ray vector nanotomography. Nature, 547(7663), 328–331.
Fernández-Pacheco, A., Streubel, R., Fruchart, O., Hertel, R., Fischer, P., & Cowburn, R. P. (2017). Three-dimensional nanomagnetism. Nature Communications, 8, 15756.
Lewis, G. R., Loudon, J. C., Tovey, R., Chen, Y.-H., Roberts, A. P., Harrison, R. J., Midgley, P. A., & Ringe, E. (2020). Magnetic Vortex States in Toroidal Iron Oxide Nanoparticles: Combining Micromagnetics with Tomography. Nano Letters, 20(10), 7405–7412.
You can find out about applying for this project on the Department of Earth Sciences page.
Prof Richard Harrison
Department of Earth Sciences Graduate Administrator