Magnon-assisted tunnelling in van der Waals heterostructures based on CrBr 3
The growing family of two-dimensional (2D) materials1-3 can be used to assemble van der Waals heterostructures with a wide range of properties4-6 . Of particular interest are tunnelling heterostructures7-9 , which have been used to study the electronic states both in the tunnelling barrier and in the emitter and collector contacts10,11. Recently, 2D ferromagnets have been studied theoretically12-15 and experimentally16-18 . 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 tunnelling8,19-21 or by tunnelling through localised states8,21,22 . In the case of our ferromagnetic barrier the dominant tunnelling mechanisms are the emission of magnons18 at low temperatures or scattering of electrons on localised magnetic excitations above the Curie temperature. Magnetoresistance in the graphene electrodes further suggests induced spin-orbit coupling and proximity exchange via the ferromagnetic barrier. Tunnelling with magnon emission offers the possibility of spin-injection, as has been previously demonstrated with other ferromagnetic barriers23,24 .