2D-MTJs: introducing 2D materials in magnetic tunnel junctions

This review focuses on the recent experimental integration of 2D materials, mostly graphene but also h-BN and dichalochogenides, such as MoS2 and WS2, in magnetic tunnel junctions. The main remarkable characteristic of 2D materials is the ability to gain high homogeneous atomic control over their thickness, as this is barely achievable with the usual 3D materials deposited through conventional physical vapour deposition (PVD) growth techniques. This could become a critical asset for spintronics with regard to the fabrication of spin valves, where ultra-thin layers with extreme control are targeted, especially for spin-polarized electron tunnelling. A complete overview of the state of the art is presented, and the different integrative pathways of 2D materials with ferromagnets are addressed, including the exfoliation of 2D flakes from crystals, the wet transfer steps of large scale layers, and direct chemical vapour deposition (CVD) growths catalysed on ferromagnetic electrodes. Interestingly, these recent experiments have already highlighted some novel properties that emanate from 2D-based heterostructures, such as passivation against oxidation diffusion and augmented spin filtering at the interface. Many perspectives are thus being opened up in the exploration of the vast amount of 2D material families and their association in heterostructures, targeting specific spin device properties.