Multiple helimagnetic phases and topological Hall effect in epitaxial thin films of pristine and Co-doped SrFeO3

We report magnetotransport properties for epitaxial thin films of SrFeO${}_{3}$ and SrFe${}_{0.99}$Co${}_{0.01}$O${}_{3}$ with possible skyrmion-related spin textures. Resonant soft x-ray diffraction measurements revealed formation of helical spin structures for both samples ($Q//\ensuremath{\langle}111\ensuremath{\rangle}$). From magnetotransport measurements we found several distinct helimagnetic phases with multiple/single $Q$ vectors. A steep suppression of Hall resistivity is observed above the critical field to reach the high-field conical state, indicating the presence of skyrmionlike topological spin textures at lower fields responsible for the topological Hall effect.