Topological Hall Effect due to Skyrmions in Magnetic Multilayers

Understanding the relationship between skyrmions and the behaviour of the Hall effect is essential to realise skyrmionic data storage. In this thesis, possible contributions to the Hall effect, anomalous and topological, in [CoB/Ir/Pt]xn multilayers are determined and the temperature and repeat layer, n, dependent behaviour characterised. The excess Hall resistivity remaining after the ordinary and anomalous Hall effects are subtracted from the Hall resistivity is measured in CoB/Ir/Pt multilayers and shown to depend on the temperature and n. The number, and variation in number, of peak and trough-like features in ρxy,excess as the magnetic field is varied is inversely proportional to the temperature and n. Correlation between the temperature dependence of maximum ρxy,excess signal and anomalous contribution, ρA, is observed possibly suggesting shared physical origins between ρxy,excess and ρA. The observations reported suggest that ρxy,excess is, at least partially, topological in nature. This is supported by the dependence of maximum ρxy,excess on n in agreement with previous reports of skyrmion presence in similar multilayer samples with 2 <= n <=10. The temperature dependence of the anomalous Hall effect in [CoB|Ir|Pt]xn is accounted for by the temperature dependence of the saturation magnetisation, MS(T). Extrinsic (skew scattering, α, and side-jump, β) and intrinsic (b) contributions to the anomalous Hall effect are determined by scaling with longitudinal resistivity, ρxx. The AHE is described well in these samples by summing linear and quadratic terms in ρxx0 from impurity scattering, and a quadratic term in ρxx from phonon-lattice interactions. α, β, and b are of similar magnitude to those found in literature for single-layered ferromagnetic materials. Side-jump scattering is found to be the largest contribution to the anomalous Hall resistivity in [CoB|Ir|Pt]×n multilayers suggesting that the large side-jump coefficient observed could be contributing to the temperature dependence of ρxy,excess.