Magnetic-Field-Tuned Critical End Point and High-Field Phases in HoMn₆Sn₆

Topological Kagome RMn₆Sn₆ materials exhibit a rich variety of magnetic phases which provide an opportunity to understand how different spin textures affect topological and transport properties through the application of strong magnetic fields. We report experiments on single-crystal HoMn₆Sn_6, made possible by pulsed magnetic fields of up to 60 T, that permit high-field features of the field-temperature phase diagram to be studied in detail using magnetometry. Complementary, sensitive transport experiments over the same field range employ novel focused-ion-beam fabrication of strain-relieved HoMn₆Sn₆ devices. In accordance with mean-field calculations, we find a metamagnetic transition at 45 T with H || c between canted phases that ends in a liquid-gas-like critical end point at about 90 K. As far as we are aware, this is the only critical end-point that occurs within the RMn₆Sn₆ kagome metals, and its temperature and field far exceed those of analogous phenomena in other materials. In the low-temperature metamagnetic region, HoMn₆Sn₆ shows large magnetoresistance, reaching 900 % at 60 T in concert with Shubnikov de Haas oscillations that suggest Fermi-surface contraction above 45 T, whilst non-trivial band topology is maintained. Near the critical end point, we find deviations from Fermi-liquid behavior in the temperature-dependent magnetoresistance. The Hall resistivity above 45 T indicates that the dominant carries are holes. In the metamagnetic region, the anomalous Hall contribution is not proportional to the magnetization, and peaks at about 40 K, suggesting the role of enhanced spin fluctuations near the critical point.