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

Abstract

Topological Kagome RMn6Sn6 materials, where R is a rare-earth, 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 magnetic field H. In this work, we report experiments on single-crystal HoMn6Sn6, 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 focused-ion-beam fabrication of novel strain-relieved HoMn6Sn6 devices. In agreement with meanfield calculations, we find a metamagnetic transition at 45 T with H||c between canted phases that ends in a critical end point at about 90 K. As far as we are aware, this is the only critical endpoint that is observed 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 a slight Fermi-surface contraction as the metamagnetic transition is crossed. A phase analysis of the oscillations suggests non-trivial band topology, although a firmer attribution must await detailed bandstructure calculations. Near the critical end point, we find deviations from Fermi-liquid behavior in the temperature-dependent magnetoresistance. In the metamagnetic region, the anomalous Hall contribution is not proportional to magnetization, and peaks at about 40 K, suggesting the role of enhanced spin fluctuations near the critical point. At higher temperatures, the anomalous Hall effect reappears at low fields, showing that the magnetization provided by the Ho and Mn sublattices independently affect the conductivity.