Data-Driven Engineering of Spin Injection in Magnetic Tunnel Junctions Based on van der Waals Materials

Demonstration of magnetism in two-dimensional materials (2DMs) has enabled the production of magnetic tunnel junctions (MTJ) in van der Waals heterostructures. Since then, the search for MTJs with improved properties (e.g. enhanced tunnel magneto-resistance and spin injection) has spawned considerable efforts. However, unlike bulk magnetic tunnel junctions, the absence of epitaxial restrictions within the growing family of 2DMs yields an extremely large number of possible heterostructures and pose a daunting challenge for both experimental and computational efforts. Hence, guiding principles for the creation and optimization of the properties of these layered heterostructures is highly desirable.<br/>Here we show that optimal spin injection in these systems can be realized through band engineering. First, we demonstrate that quantum transport calculations within the Landauer’s formalism quantitatively describe spin injection in these heterostructures, as exemplified in graphite/CrI₃ junctions [1]. More importantly, we find that, owing to the weak van der Waals interactions between layers, the emerging properties of the MTJs formed with 2DMs can be rationalized in terms of the bulk properties of its constituents [2]. This feature enables spin injection control using descriptors obtained from first principles that include complex band structure, band alignment, density of states, circumventing computationally demanding quantum transport calculations. Through this approach, we demonstrate that the choice of electrodes within the family of transition metal dichalcogenides may increase the spin injection in CrI₃ junctions by various orders of magnitude and improve tunneling magnetoresistance. We also apply the methodology to magnetic heterostructures combining transition metal dichalcogenides and halides and find other suitable MTJ candidate heterostructures. By screening possible 2DM constituents based on their bulk properties, our work may prove useful to the accelerated rational design of magnetic heterostructures based on van der Waals materials.<br/>The authors gratefully acknowledge the support from the National Science Foundation (NSF) through Grant No. NSF-1848344. A.M.P. is thankful for the support from the Alabama EPSCoR GRSP.<br/>[1] Heath et al., "Role of quantum confinement and interlayer coupling in CrI₃-graphene magnetic tunnel junctions", Physical Review B <b>101</b>, 195439 (2020).<br/>[2] Heath and Kuroda, "Spin-Injection Enhancements in van der Waals Magnetic Tunnel Junctions through Barrier Engineering", Phys. Rev. Applied <b>16</b>, L041001 (2021).