We developed a surface roughness model for magnetic systems, by taking into account the space-dependent uniaxial anisotropy and Dzyaloshinskii-Moriya interaction (DMI). The spacial variation is determined by the surface topography of multilayer structure, which is characterised by atomic force microscopy. By using micromagnetic technique, we found that the DMI is required for the stabilisation of meron-like spin textures in an in-plane magnetised [Pt/Co/Ta] trilayer structure. Furthermore, with the presence of surface roughness, much larger textures can be stabilised with lateral dimensions from 0.2 to 2 μm, in agreement with experimental observations. Please find more out in our published paper!
(Abstract) Interfacing magnetic materials with non-magnetic heavy metals with a large spin-orbit coupling, such as Pt, results in an asymmetric exchange interaction at the interface due to the Dzyaloshinskii-Moriya interaction (DMI), which in turn leads to the formation of skyrmions and topological spin structures in perpendicularly magnetised multilayers. Here we show that out of plane spin structures with lateral dimensions from 200 nm to 2μm are stabilised in in-plane magnetised Ta/Co/Pt trilayer structures. We show that these spin textures are largely insensitive to the direction of the in-plane magnetisation switched by either magnetic fields or electric fields applied across a Si3N4 gate dielectric. The results of micromagnetic simulations indicate that DMI is required for the stabilisation of such out of plane domains and that the presence of surface roughness helps to stabilise larger structures, in agreement with experimental results. We identify these spin structures as meron-like topological textures, characterized by a perpendicular spin texture in an uniformly in-plane magnetised system.
J. Vijayakumar, Y. Li, D. Bracher, C. W. Barton, M. Horisberger, T. Thomson, J. Miles, C. Moutafis, F. Nolting, and C.A.F. Vaz*
Physical Review Applied 14, 054031 (2020).