In the presence of a perpendicular magnetic field, the trajectory of electrons is curved, which leads to a transverse voltage: this is the Hall effect. When electrons travels through certain types of non-collinear spin textures – such as skyrmions – they also experience the equivalent of a magnetic field, which produces a “topological” Hall effect. In magnetic thin films with perpendicular magnetic anisotropy, magnetization may reverse by the formation of bubbles that in some cases possess a spin structure similar to that of skyrmions. In our recent paper just out in Nature Physics, we have measured a large topological Hall effect in thin films of a weakly doped metallic manganite (Ce,Ca)MnO3. Its parent compound – CaMnO3 – is a Mott insulator, i.e. a material showing an insulating character due to strong repulsion effects between electrons (coined strong correlations). Magnetic force microscopy images reveal the presence of magnetic bubbles whose density shows a magnetic field dependence akin to that of the topological Hall effect. Interestingly, the amplitude of the effect strongly increases as Ce doping is reduced and the materials approaches the Mott insulating state, which suggests that the topological Hall effect is enhanced by strong correlations.
This work was performed in collaboration with Rutgers University, Nagoya University, ICMAB Barcelona and the Universidad Complutense de Madrid
Giant topological Hall effect in correlated oxide thin films
L. Vistoli et al, Nature Phys. doi:10.1038/s41567-018-0307-5 (2018)