Researchers from the National University of Singapore, University of Manchester and National Institute for Materials Science have shown that magnetic proximity can be used to electrically control large spin signals in graphene superlattices, achieving spin polarizations approaching 50% and nonlocal spin resistances above 300 Ω near charge neutrality.
By placing graphene in close proximity to a magnetic material, they induce a magnetic proximity effect that spin-splits graphene’s bands via interfacial exchange coupling, without permanently magnetizing the carbon lattice or degrading its intrinsic transport properties. In their devices, cobalt contacts are used to generate this exchange field, while pure spin currents are injected and detected nonlocally, allowing the team to map how spin transport responds as the Fermi level is tuned across different charge density regimes.
Near the charge neutrality point (CNP) in monolayer graphene, where the carrier density is very low, the researchers observe a gate-tunable inversion of the nonlocal spin signal. This inversion arises from asymmetric spin injection into proximity-split conduction and valence bands, and constitutes a direct signature of exchange-induced band reconstruction in graphene.
When monolayer graphene is precisely aligned with hexagonal boron nitride to form a superlattice, additional “satellite” neutrality points appear in the miniband structure, and similar spin-signal inversions are detected at these points as well. The fact that the same behavior is observed at both the primary and satellite neutrality points shows that proximity-induced spin splitting governs spin transport not only in graphene’s original Dirac bands, but also in the reconstructed minibands created by the moiré superlattice. As University of Manchester's Dr. Daniel Burrow notes, "Our measurements show that the same underlying mechanism controls spin transport across all these regimes," emphasizing that the effect is robust rather than device-specific.
The strongest spin signals are obtained in a doubly aligned bilayer graphene superlattice, where an electric-field-induced bandgap allows for strong energy-selective spin filtering. In this configuration, the team measures effective spin polarizations approaching 50% and nonlocal spin resistances exceeding 300 Ω near the relevant neutrality point, values that are nearly two orders of magnitude larger than those found away from charge neutrality in the same platform. This enhancement arises from the combination of low carrier density, proximity-induced spin splitting, and a tunable bandgap that preferentially transmits one spin species over a narrow energy window. Because the bandgap in bilayer graphene can be controlled electrostatically, the degree of spin filtering and the magnitude of the spin signal can be tuned purely with gate voltages, without altering the magnetic contacts or device geometry.
Across the monolayer, aligned monolayer, and doubly aligned bilayer devices, the experiments establish pure spin transport as a sensitive probe of magnetic band reconstruction in graphene-based heterostructures. The observed spin-signal inversions at primary and satellite neutrality points, together with the large spin polarization and nonlocal spin resistance in gapped bilayer superlattices, all point to a single underlying mechanism: magnetic proximity-induced spin splitting of graphene’s bands.
These signatures persist up to room temperature, indicating that the proximity-induced spin texture is robust enough for realistic device operation. As University of Manchester's Dr. Jesus Toscano Figueroa puts it, "This research shows that we can engineer graphene systems where spin signals become both large and electrically tunable," highlighting the potential of such proximitized graphene superlattices for future low-power spintronic technologies that process information using spin rather than charge.