Magneto thermal conductivity and thermal Hall conductivity of single crystal MnBi through the spin-reorientation temperature range

The search for an experimental signature in transport properties of magnetic topological materials is a major thrust in materials research. MnBi, a hard hexagonal ferromagnet with a high Curie temperature and strong spin-orbit interactions, is a great candidate to investigate this due to two properties.  First, it has a unique spin reorientation (SR) behavior: under about 90 K the spins align in the ab-plane, above about 140 K the spins align along the c-axis, and in between 90 and 140 K the spins have some degree of freedom between these two extremes.¹ Second, it has an extremely large anomalous Nernst conductivity that is not simply explained by the band structure.² Here, we explore the magneto thermal conductivity and thermal Hall conductivity of MnBi and study the structure and topology of the domains using Lorentz Transmission Electron Microscopy to identify the correlation between thermal transport properties and the topological properties of the domains in the SR regime. We show that the domain growth in an applied magnetic field causes a large decrease in magneto thermal conductivity and interesting trends in thermal Hall conductivity; however, this process is complex in the SR temperature regime.

[1] McGuire et al.  PRB 90, 174425 (2014)

[2] He et al., Joule 5 1-11 (2021)