Three-dimensional magnetic systems: the future is bright!

Claire Donnelly, University of Cambridge

Three dimensional magnetic systems promise significant opportunities for applications, for example providing higher density devices and new functionalities associated with complex topology and greater degrees of freedom [1,2]. With recent advances in both characterization and nanofabrication techniques, the experimental investigation of these complex systems is now possible, opening the door to the elucidation of new properties and rich physics.
For the characterization of 3D nanomagnetic systems, we have developed techniques to map both the three-dimensional magnetic structure, and its response to external excitations. In a first demonstration of X-ray magnetic nanotomography [3,4], we determined the complex magnetic structure within the bulk of a μm-sized soft magnetic pillar. The magnetic configuration contained vortices and antivortices, as well as Bloch point singularities [3]. With these new datasets comes a new challenge concerning the identification of such nanoscale topological objects within complex reconstructed magnetic configurations. To address this, we have recently implemented calculations of the magnetic vorticity [5,6], that make possible the location and identification of 3D magnetic solitons, leading to the first observation of nanoscale magnetic vortex rings [6].
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 [7,8], it is now possible to determine the magnetisation dynamics of a three-dimensional magnetic system [7].
Finally, recent advances in nanofabrication make possible the fabrication of complex 3D magnetic nanostructures [9], leading to the realisation of artificial chiral structures [10] and 3D spintronic devices [11]. These new experimental capabilities for 3D magnetic systems open the door to complex three-dimensional magnetic structures, and their dynamic behaviour.

PDF file of the talk available here

[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., “Tomographic reconstruction of a three-dimensional magnetization vector field” New Journal of Physics 20, 083009 (2018).
[5] Cooper, “Propagating magnetic vortex rings in ferromagnets.” PRL. 82, 1554 (1999).
[6] Donnelly et al., “Experimental observation of vortex rings in a bulk magnet” Nat. Phys. (2020)
[7] Donnelly et al., “Time-resolved imaging of three-dimensional nanoscale magnetization dynamics”, Nature Nanotechnology 15, 356 (2020).
[8] Witte, et al., “From 2D STXM to 3D Imaging: Soft X-ray Laminography of Thin Specimens”, Nano Lett. 20, 1305 (2020).
[9] Skoric et al., “Layer-by-Layer Growth of Complex-Shaped Three-Dimensional Nanostructures with Focused Electron Beams” Nano Lett. 20, 184 (2020).
[10] Sanz-Hernández et al., “Artificial Double-Helix for Geometrical Control of Magnetic Chirality” ACS Nano 14, 8084 (2020).
[11] Meng et al., “Non-planar geometrical effects on the magnetoelectrical signal in a three-dimensional nanomagnetic circuit” In preparation.