Origin of the hump anomalies in the Hall resistance loops of ultrathin SrRuO3/SrIrO3 multilayers

The proposal that very small Neel skyrmions can form in SrRuO3/SrIrO3 epitaxial bilayers and that the electric field effect can be used to manipulate these skyrmions in gated devices strongly stimulated the recent research of SrRuO3 heterostructures. A strong interfacial Dzyaloshinskii-Moriya interaction was considered as the driving force for the formation of skyrmions in SrRuO3/SrIrO3 bilayers. Here, we investigated nominally symmetric heterostructures in which an ultrathin ferromagnetic SrRuO3 layer is sandwiched between large spin-orbit coupling SrIrO3 layers, for which the conditions are not favorable for the emergence of a net interfacial Dzyaloshinskii-Moriya interaction. Previously the formation of skyrmions in the asymmetric SrRuO3/SrIrO3 bilayers was inferred from anomalous Hall resistance loops showing humplike features that resembled topological Hall effect contributions. Symmetric SrIrO3/SrRuO3/SrIrO3 trilayers do not show hump anomalies in the Hall loops. However, the anomalous Hall resistance loops of symmetric multilayers, in which the trilayer is stacked several times, do exhibit the humplike structures, similar to the asymmetric SrRuO3/SrIrO3 bilayers. The origin of the Hall effect loop anomalies likely resides in unavoidable differences in the electronic and magnetic properties of the individual SrRuO3 layers rather than in the formation of skyrmions.

Automated summary

Research has shown that very small Neel skyrmions can potentially form in SrRuO3/SrIrO3 epitaxial bilayers, and the electric field effect can be used to manipulate these skyrmions. Meanwhile, symmetric SrIrO3/SrRuO3/SrIrO3 trilayers exhibit anomalous Hall resistance loops similar to those in asymmetric bilayers.