LAUSR

We report the critical role of La doping in the topological Hall effect observed in LaxEu1-xO thin films (~ 50 nm) grown by molecular beam epitaxy. When the La doping exceeds 0.036, topological Hall effect emerges, which we attribute to the formation of magnetic skyrmions. Besides, the La doping is found to play a critical role in determining the phases, densities, and sizes of the skyrmions in the LaxEu1-xO thin films. The maximum region of the skyrmion phase diagram is observed on the La0.1Eu0.9O thin film. As the La doping increases, the skyrmion density increases while the skyrmion size decreases. Our findings demonstrate the important role of La doping for the skyrmions in EuO films, which could be important for future studies of magnetic skyrmions in Heisenberg ferromagnets.