Artificial Ferroic Systems: Magnetic Monopoles, Chirality and Bloch Point Singularities

In artificial ferroic systems [1], novel functionality is engineered through the combination of designed ferroic structures and the control of the interactions between the different components. We probe their behaviour with large-scale facility methods including synchrotron x-rays and low energy muon spectroscopy, which give unparalleled information on microscopic magnetic phenomena.
In hybrid mesoscopic structures incorporating two different ferromagnetic layers, the static and dynamic behaviour result from the mutual imprint of the magnetic domain configurations. Here, vortex core reversal can be induced by displacing the core across a domain boundary with a magnetic field. This reversal occurs via the creation of a pair of Bloch point singularities [2].
In artificial spin ice, consisting of arrays of dipolar-coupled nanomagnets arranged in frustrated geometries, a number of interesting emergent phenomena occur. For example, we have observed the creation and separation of emergent magnetic monopoles in an applied magnetic field [3]. In thermally-active systems with superparamagnetic elements, there is a geometry-dependent evolution of magnetic configurations into the lowest-energy states [4], and this dynamic process can be chiral [5]. We have also demonstrated that these magnetic metamaterials can support thermodynamic phase transitions [6, 7]. Finally, we have developed synchrotron x-ray methods to obtain chemical, structural and magnetic information in 3D, and have directly observed the curling magnetic structure surrounding Bloch points [8].
[1] L.J. Heyderman and R.L. Stamps, JPCM (2013); [2] P. Wohlhuter et al. Nat Commun (2015); [3] E. Mengotti et al. Nature Phys (2011); [4] A. Farhan et al. Nature Phys and PRL (2013); [5] S. Gliga et al. Nat Mater (2017); [6] L. Anghinolfi et al. Nat Commun (2015); [7] N. Leo et al. Nat Commun (2018); [8] C. Donnelly et al. PRL (2015) and Nature (2017)