Exploring unconventional magnets with nanoscale coherent X-ray imaging

In recent years there has been a surge of interest in nanoscale magnetic configurations with non-trivial topologies, that not only represent a platform for topology, but offer opportunities for energy efficient technological devices. Key to understanding – and harnessing! – such materials and their configurations is the ability to visualise them on the nanoscale. Indeed, their nanoscale ordering and phenomena determine their macroscopic properties.

To that end, we aim to use X-ray coherent diffractive imaging (see figure 1), a lensless technique that offers ultra-high spatial resolution of nanoscale phenomena. So far, this has been combined with imaging of ferromagnets – in both two [1] and three dimensions [2, 3] – offering key insights into the formation of textures such as singularities of the magnetisation [2] (see figure 2). However, the study of nanoscale phenomena in more complex, unconventional magnets, from compensated antiferromagnets to spin spiral-hosting materials and the recently discovered altermagnets [4], remains challenging.

In this PhD project, we aim to combine coherent diffractive imaging with advanced X-ray spectroscopy to map, and understand, unconventional magnets at the nanoscale. The PhD project will involve working with international collaborators, both on the growth of materials, and the development of spectroscopic coherent imaging at synchrotron X-ray facilities. By performing advanced analysis of our spectroscopic coherent imaging data, we aim to obtain key insights into the physics of these magnetic systems.

[1] J. Neethirajan, B.J. Daurer, M. Di Pietro Martínez, A. Hrabec, L. Turnbull, R. Yamamoto, M. Raboni Ferreira, A. Štefančič, D.A. Mayoh, G. Balakrishnan, Y. Pei, P. Xue, L. Chang, E. Ringe, R. Harrison, S. Valencia, M. Kazemian, B. Kaulich, and C. Donnelly
Soft X-Ray Phase Nanomicroscopy of Micrometer-Thick Magnets
Phys. Rev. X 14, 031028 (2024)
[2] C. Donnelly, M. Guizar-Sicairos, V. Scagnoli, S. Gliga, M. Holler, J. Raabe, and L.J. Heyderman 
Three-dimensional magnetization structures revealed with X-ray vector nanotomography
Nature 547, 328–331 (2017)
[3] A. Apseros, V. Scagnoli, M. Holler, M. Guizar-Sicairos, Z. Gao, C. Appel, L.J. Heyderman, C. Donnelly, J. Ihli
X-ray Linear Dichroic Tomography of Crystallographic and Topological Defects
arXiv:2402.10647, accepted for publication in Nature (2024)
[4] Altermagnetism imaged and controlled down to the nanoscale
O. J. Amin, A. Dal Din, E. Golias, Y. Niu, A. Zakharov, S. C. Fromage, C. J. B. Fields, S. L. Heywood, R. B. Cousins, J. Krempasky, J. H. Dil, D. Kriegner, B. Kiraly, R. P. Campion, A. W. Rushforth, K. W. Edmonds, S. S. Dhesi, L. Šmejkal, T. Jungwirth, P. Wadley
arXiv:2405.02409

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