Max Hirschberger
Recently, we have explored a variety of metallic materials where non-coplanar magnetic order occurs on characteristic length scales λ comparable to the size of a single crystallographic unit cell. In this limit, the standard (real-space) model of the ‘topological’ Hall effect, the key transport signature of Berry curvature due to canted magnetism, is expected to fail. In metallic magnets where the carrier mean free path exceeds λ, a momentum-space picture of the THE is expected to be more appropriate for an adequate description.
We aim to approach the momentum space regime using four model compounds, listed here in order of decreasing λ: (1) In rare-earth magnets with inversion center such as Gd2PdSi3 and Gd3Ru4Al12, we observed nanometer-sized skyrmion textures in highly symmetric lattices and in absence of Dzyaloshinskii-Moriya interactions (λ~2-3 nm). (2) The (breathing) Kagome system Dy3Ru4Al12 realizes a peculiar arrangement of antiferromagnetically stacked canted spin-trimers (λ~1-2 nm). (3) The metallic pyrochlore oxide Nd2Mo2O7 is a canted ferromagnet where non-coplanarity occurs within a single unit cell (λ~1 nm).
The topological Hall and Nernst effects of these materials were studied while tuning a variety of ‘external knobs’. We changed the Fermi energy via substitutional doping and also modified the lattice spacing via hydrostatic pressure. Thus, we aim to develop new phenomenology of transport signatures characteristic in the limit of entangled real-space canted magnetism and momentum space Berry curvature.