Probing magnetism in atomically thin van der Waals insulators using electron tunneling

Layered magnetic insulators that can be exfoliated are highly desirable, as we can potentially create topological states (e.g. quantum anomalous Hall effect) by incorporating them in van der Waals heterostructures. Such materials were finally realized in 2017 with the isolation of monolayer CrI₃ and bilayer CrGeTe₃. However, this field is in its infancy and few layer films seem to have complex properties different from bulk, such as the ferromagnetic to antiferromagnetic transition in CrI₃. In this talk, I will discuss the use of electron tunneling through ultrathin magnetic insulators as a probe of their magnetic ground state and excitations [1]. We report giant magnetoresistance effects when tunneling through CrI₃ and CrCl₃ barriers with graphite electrodes, resulting from polarization of their antiferromagnetic ground states under an applied magnetic field. In CrI₃ we also find inelastic electron tunneling suggesting the observation of Dirac magnon excitations. Finally, we note a large enhancement of the interlayer exchange in thin CrCl₃ compared to bulk, and discuss its origins.

1. D. R. Klein, D. MacNeill, J. L. Lado, D. Soriano, E. Navarro-Moratalla, K. Watanabe, T. Taniguchi, S. Manni, P. Canfield, J. Fernández-Rossier, P. Jarillo-Herrero, Science 360, 1218 (2018).