Graphene and the large families of 2D materials (2DMs) introduced recently have a wealth of interesting properties to offer. Their use in spintronics is somehow a natural idea as spin devices (such as MRAMs) rely strongly on interfacial properties of ultrathin films, and 2DMs are exactly that: a perfectly crystalline interface with control at the atomic level.
In their recent review, Maëlis Piquemal-Banci and her team at the Unité Mixte de Physique CNRS-Thales in France retrace the last decade of effort to use 2DMs in the prototypical spintronics device, the magnetic tunnel junction.
The main challenge concerns 2DM integration with delicate and oxidation-prone ferromagnets used as spin sources. Up to now, to derive graphene layers on ferromagnets relied on the celebrated scotch tape method introduced in 2004 by Geim and Novoselov. However, in the particular case of spintronics, this approach usually leads to contaminated interfaces. Interestingly, an alternative successful trend emerges as more and more experiments make use of direct chemical vapor deposition (CVD) processes for integration of 2DMs.
By taking advantage of catalysis phenomena, these CVD processes provide a means to directly grow the 2D crystals on ferromagnet surfaces, which results in high quality interfaces. Already, novel properties of 2DM-ferromagnet interfaces have been demonstrated thanks to this approach. Beyond large spin signals, the authors highlight results concerning protection against oxidation/diffusion at ferromagnetic interfaces, the unlocking of low-cost atomic layer deposition (ALD) processes for spintronics, and novel spin filtering effects observed in experiments. But the field of 2D-based magnetic tunnel junctions is just unfolding as many new 2DMs are being isolated, and their large scale growth is just on the verge of being developed. This opens many perspectives for the fabrication of layered spin devices, with foreseeable opportunities for the control of spin flows in tailored hetero-structures of 2D crystals.
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Categories: Journal of Physics D: Applied Physics