Observation of magnetic vortex pairs at room temperature in a planar α-Fe ₂ O ₃/Co heterostructure

Chmiel, Francis P., Waterfield Price, Noah, Johnson, Roger D., Lamirand, Anne D., Schad, Jon, van der Laan, Gerrit, Harris, David T., Irwin, Julian, Rzchowski, Mark S., Eom, Chang-Beom and Radaelli, Paolo G. (2018) Observation of magnetic vortex pairs at room temperature in a planar α-Fe ₂ O ₃/Co heterostructure. Nature Materials, 17 (7), 581-585. (doi:10.1038/s41563-018-0101-x).

Abstract

Vortices, occurring whenever a flow field ‘whirls’ around a one-dimensional core, are among the simplest topological structures, ubiquitous to many branches of physics. In the crystalline state, vortex formation is rare, since it is generally hampered by long-range interactions: in ferroic materials (ferromagnetic and ferroelectric), vortices are observed only when the effects of the dipole–dipole interaction are modified by confinement at the nanoscale1,2,3, or when the parameter associated with the vorticity does not couple directly with strain4. Here, we observe an unprecedented form of vortices in antiferromagnetic haematite (α-Fe2O3) epitaxial films, in which the primary whirling parameter is the staggered magnetization. Remarkably, ferromagnetic topological objects with the same vorticity and winding number as the α-Fe2O3 vortices are imprinted onto an ultra-thin Co ferromagnetic over-layer by interfacial exchange. Our data suggest that the ferromagnetic vortices may be merons (half-skyrmions, carrying an out-of plane core magnetization), and indicate that the vortex/meron pairs can be manipulated by the application of an in-plane magnetic field, giving rise to large-scale vortex–antivortex annihilation.

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