Evolution of chiral magnetic textures and their topological Hall signature in Ir/Fe/Co/Pt multilayer films

We establish a direct correspondence between skyrmions and their topological Hall signature in multilayer films by combining transport and magnetic force microscopy measurements over a wide range of temperature and applied magnetic field (H). First, we demonstrate the relationship between the areal density of isolated skyrmions and the magnitude of THE over a 200 K temperature range for fixed fields near saturation. Second, as H is swept towards zero, we find that skyrmions aggregate to form worm-like magnetic textures, which carry a large topological charge, and manifest as peaks in the measured THE. Quantitative modelling of these worm textures allows us to explain the field and temperature evolution of THE. Notably, we identify a much larger topological Hall resistivity than prevailing theory predicts for the observed skyrmion density. We suggest that band structure plays an important role in the skyrmion–current coupling, with implications for the impact of the Berry-phase of skyrmions on charge carriers.