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High-TC cuprate superconductors' growth conditions and their incompatibility with some of the most standard nanofabrication approaches make their large-scale integration with 2D materials (such as graphene, transition metal dichalcogenides, and other Van der Waals materials) much more difficult than for conventional, metallic superconductors. Here, we address this challenge and develop an approach based on pulsed laser deposition that allows the growth of the 2D semiconductor MoS2 on the archetypal high-TC superconductor YBa2Cu3O7−x. This yields functional heterostructures in which the individual constituents' properties are preserved and that show superconducting coupling across their interface. The developed approach paves the way for large-scale 2D semiconductor co-integration with high-TC superconductors toward the study and leverage of the superconducting proximity effect in hybrid devices. [ABSTRACT FROM AUTHOR]

2D materials offer the ability to expose their electronic structure to manipulations by a proximity effect. This could be harnessed to craft properties of 2D interfaces and van der Waals heterostructures in devices and quantum materials. We explore the possibility to create an artificial spin polarized electrode from graphene through proximity interaction with a ferromagnetic insulator to be used in a magnetic tunnel junction (MTJ). Ferromagnetic insulator/graphene artificial electrodes were fabricated and integrated in MTJs based on spin analyzers. Evidence of the emergence of spin polarization in proximitized graphene layers was observed through the occurrence of tunnel magnetoresistance. We deduced a spin dependent splitting of graphene's Dirac band structure (∼15 meV) induced by the proximity effect, potentially leading to full spin polarization and opening the way to gating. The extracted spin signals illustrate the potential of 2D quantum materials based on proximity effects to craft spintronics functionalities, from vertical MTJs memory cells to logic circuits.

We present a bias-controlled spin-filtering mechanism in spin-valves including a hybrid organic chain/graphene interface. Wet growth conditions of oligomeric molecular chains would usually lead, during standard CMOS-compatible fabrication processes, to the quenching of spintronics properties of metallic spin sources due to oxidation. We demonstrate by X-ray photoelectron spectroscopy that the use of a protective graphene layer fully preserves the metallic character of the ferromagnetic surface and thus its capability to deliver spin polarized currents. We focus here on a small aromatic chain of controllable lengths, formed by nitrobenzene monomers and derived from the commercial 4-nitrobenzene diazonium tetrafluoroborate, covalently attached to the graphene passivated spin sources thanks to electroreduction. A unique bias dependent switch of the spin signal is then observed in complete spin valve devices, from minority to majority spin carriers filtering. First-principles calculations are used to highlight the key role played by the spin-dependent hybridization of electronic states present at the different interfaces. Our work is a first step towards the exploration of spin transport using different functional molecular chains. It opens the perspective of atomic tailoring of magnetic junction devices towards spin and quantum transport control, thanks to the flexibility of ambient electrochemical surface functionalization processes.

A crystallographically heterogeneous interface was fabricated by growing hexagonal graphene (Gr) using chemical vapor deposition (CVD) on a tetragonal FePd epitaxial film grown by magnetron sputtering. FePd was alternately arranged with Fe and Pd in the vertical direction, and the outermost surface atom was identified primarily as Fe rather than Pd. This means that FePd has a high degree of L 1 0 -ordering, and the outermost Fe bonds to the carbon of Gr at the interface. When Gr is grown by CVD, the crystal orientation of hexagonal Gr toward tetragonal L 1 0 -FePd selects an energetically stable structure based on the van der Waals (vdW) force. The atomic relationship of Gr/ L 1 0 -FePd, which is an energetically stable interface, was unveiled theoretically and experimentally. The Gr armchair axis was parallel to FePd [100] L 10 , where Gr was under a small strain by chemical bonding. Focusing on the interatomic distance between the Gr and FePd layers, the distance was theoretically and experimentally determined to be approximately 0.2 nm. This shorter distance (≈0.2 nm) can be explained by the chemisorption-type vdW force of strong orbital hybridization, rather than the longer distance (≈0.38 nm) of the physisorption-type vdW force. Notably, depth-resolved X-ray magnetic circular dichroism analyses revealed that the orbital magnetic moment ( M l ) of Fe in FePd emerged at the Gr/FePd interface (@inner FePd: M l = 0.16 μ B → @Gr/FePd interface: M l = 0.32 μ B ). This interfacially enhanced M l showed obvious anisotropy in the perpendicular direction, which contributed to interfacial perpendicular magnetic anisotropy (IPMA). Moreover, the interfacially enhanced M l -FePd. A micromagnetic simulation assuming both PMA and IPMA predicted that perpendicularly magnetized magnetic tunnel junctions (p-MTJs) using Gr/ M l emerged at the crystallographically heterogeneous Gr/ L 1 0 -FePd p-MTJ is significant for high-density X nm generation magnetic random-access memory (MRAM) applications.L 1 0 -FePd. A micromagnetic simulation assuming both PMA and IPMA predicted that perpendicularly magnetized magnetic tunnel junctions (p-MTJs) using Gr/ L 1 0 -FePd could realize 10-year data retention in a small recording layer with a circular diameter and thickness of 10 and 2 nm, respectively. We unveiled the energetically stable atomic structure in the crystallographically heterogeneous interface, discovered the emergence of the robust IPMA, and predicted that the Gr/ L 1 0 -FePd p-MTJ is significant for high-density X nm generation magnetic random-access memory (MRAM) applications.

Epitaxial clusters of chromium and chromium-vanadium oxides are studied by tunnel magneto-resistivity measurements, x-ray absorption spectrometry and circular magnetic circular dichroism. They turn out to carry a small magnetic moment that follows a super-paramagnetic behavior. The chromium ion contribution to this magnetization is mainly due to an original magnetic Cr 2 O 3 -like phase, whereas usual Cr 2 O 3 is known to be anti-ferromagnetic in the bulk. For mixed clusters, vanadium ions also contribute to the total magnetization and they are coupled to the chromium ion spins. By measuring the dichroic signal at different temperatures, we get insight into the possible spin configurations of vanadium and chromium ions: we propose that the magnetic dipoles observed in the clusters assembly could be related to ionic spins that couple at a very short range, as for instance in short one-dimensional spins chains., (© 2022 IOP Publishing Ltd.)