Abstract

Three dimensional magnetic systems promise significant opportunities for applications, for example providing higher density devices and new functionality associated with complex topology and greater degrees of freedom [1,2]. For the experimental realisation of these new properties, appropriate characterisation techniques are required to determine both the three-dimensional magnetic structure, and its response to external excitations. In this talk, I will describe how we have made use of coherent X-rays to characterize the three-dimensional structure of magnetic systems at the nanoscale.

In particular, we have developed X-ray magnetic nanotomography [3] to access the three-dimensional magnetic configuration at the nanoscale. In a first demonstration, we have determined the complex three-dimensional magnetic structure within the bulk of a micrometre-sized soft magnetic pillar and observed a magnetic configuration that consists of vortices and antivortices, as well as Bloch point singularities [3].

In addition to the static magnetic structure, the dynamic response of the 3D magnetic configuration to excitations is key to our understanding of both fundamental physics, and applications. With our recent development of X-ray magnetic laminography [4,5], it is now possible to determine the magnetisation dynamics of a three-dimensional magnetic system [5] with spatial and temporal resolutions of 50 nm and 70 ps, respectively.

A final challenge concerns the identification of nanoscale topological objects within the complex reconstructed magnetic configurations. To address this, we have recently implemented calculations of the magnetic vorticity [6,7], that make possible the location and identification of 3D magnetic solitons, leading to the first observation of magnetic vortex rings [7].

These new experimental capabilities of X-ray magnetic imaging open the door to the elucidation of complex three-dimensional magnetic structures, and their dynamic behaviour. In the coming years, 3D magnetic imaging will benefit significantly from advances in synchrotron radiation, with associated increases in coherent flux leading to higher spatial resolutions, as well as higher throughput for in situ measurements. 

[1] Fernández-Pacheco et al., “Three-dimensional nanomagnetism” Nat. Comm. 8, 15756 (2017)
[2] Donnelly and V. Scagnoli, “Imaging three-dimensional magnetic systems with X-rays” J. Phys. D: Cond. Matt. (2019).
[3] Donnelly et al., “Three-dimensional magnetization structures revealed with X-ray vector nanotomography” Nature 547, 328 (2017).
[4] Donnelly et al., “Time-resolved imaging of three-dimensional nanoscale magnetization dynamics”, Nature Nanotechnology 15, 356 (2020).
[5] Witte, et al., “From 2D STXM to 3D Imaging: Soft X-ray Laminography of Thin Specimens”, Nano Lett. 20, 1305 (2020). 
[6] Cooper, “Propagating magnetic vortex rings in ferromagnets.” PRL. 82, 1554 (1999).
[7] Donnelly et al., “Experimental observation of vortex rings in a bulk magnet” Nat. Phys. (2020)

Biography

Claire Donnelly is currently a Leverhulme Early Career Research Fellow in the Cavendish Laboratory, University of Cambridge. Following her Masters at the University of Oxford, she went on to receive her PhD in 2017 from the ETH Zurich for her work on hard X-ray tomography of three-dimensional magnetic structures based at the Paul Scherrer Institute. Following a postdoc at the ETH Zurich, she moved to the University of Cambridge and the Cavendish in January 2019, where she is focusing on the dynamics of three-dimensional magnetic nanostructures. Her work has been recognised with a number of prizes, most recently with the European Magnetism Association Young Scientist Award.