2D Van der Waals Layers for Spintronics

Van der Waals layers for spintronic phenomena are highly interesting. We discuss all-antiferromagnetic tunnel junctions that are formed from bilayers of the van der Waals antiferromagnetic CrSBr that are twisted at angles ranging between 0 and 90 degrees. Each CrSBr layer is ferromagnetic with a strong in-plane magnetic anisotropy that results from its low symmetry. In the bulk the interlayer coupling between the CrSBr ferromagnetic layers is antiferromagnetic (AF) but twisting diminishes this interaction considerably so that we show that a device formed from two AF bilayers exhibits two non-volatile states in zero magnetic field with a giant tunnelling magnetoresistance exceeding ~700%. Nevertheless, each bilayer thus has no net magnetization, a necessity for applications where stray magnetic fields otherwise result in interactions within and between nanoscopic magnets. We show from theoretical modelling that the origin of the tunnelling magnetoresistance is via the accumulated k-dependent transmission through the individual semiconducting CrSrBr layers which depends on the twist angle[1].<br/><br/>We also discuss superconducting proximity effects in non-superconducting van der Waals layers from adjacent superconducting van der Waals layers [2]. We show that vertical Josephson junctions formed from WTe₂show a Josephson Diode effect with a large non-reciprocity in the critical supercurrent when a small magnetic field is applied perpendicular to the supercurrent within the plane of the WTe₂ flake. The diode effect strongly depends on the orientation of the magnetic field within the plane of the WTe₂ with respect to the crystal structure of the WTe₂. These results clearly indicate that the Josephson diode effect has an intrinsic origin. Such an effect could have important applications as a novel magnetic field detector at cryogenic temperatures, for example, to “read” magnetic domain walls in a cryogenic racetrack memory^*.<br/><br/><b>^*</b>Funded through an European Research Council Advanced Grant “SUPERMINT” (2022-2027).<br/> <br/><br/>[1] Y. Chen<i> et al.</i>, "Twist-assisted all-antiferromagnetic tunnel junction in the atomic limit," <i>Nature, </i>vol. 632, pp. 1045-1051, 2024.<br/>[2] J.-K. Kim<i> et al.</i>, "Intrinsic supercurrent non-reciprocity coupled to the crystal structure of a van der Waals Josephson barrier," <i>Nat. Commun., </i>vol. 15, p. 1120, 2024.