Magnon-assisted tunnelling in van der Waals heterostructures based on CrBr3

The growing family of two-dimensional (2D) materials that are now available can be used to assemble van der Waals heterostructures with a wide range of properties. Of particular interest are tunnelling heterostructures, which have been used to study the electronic states both in the tunnelling barrier and in the emitter and collector contacts. Recently, 2D ferromagnets have been studied theoretically and experimentally. Here we investigate electron tunnelling through a thin (2-6 layers) ferromagnetic CrBr3 barrier. For devices with non-magnetic barriers, conservation of momentum can be relaxed by phonon-assisted tunnelling or by tunnelling through localised states. In the case of our ferromagnetic barrier the dominant tunnelling mechanisms are the emission of magnons at low temperatures or scattering of electrons on localised magnetic excitations above the Curie temperature. Tunnelling with magnon emission offers the possibility of injecting spin into the collector electrode.