Tunnel-Barrier-Engineered Ultrafast Demagnetization and Spin Transport in Graphene-Based Heterostructures

TL;DR

This study demonstrates how ultrathin insulating barriers in graphene/ferromagnet heterostructures can be used to control ultrafast spin dynamics and magnetization processes, improving spin transport and detection.

Contribution

It introduces barrier engineering with TiOx layers to modulate interfacial spin conductance and disentangle spin pumping from magnetic proximity effects in graphene-based heterostructures.

Findings

Ultrathin TiOx barriers enable tunable ultrafast magnetic parameters.

Barrier layers reduce interfacial spin transparency and eliminate magnetic proximity effects.

Enhanced control over spin angular momentum dissipation in graphene/ferromagnet interfaces.

Abstract

Heterostructures combining graphene with 3d transition metal ferromagnets (FMs) enable various spin-based phenomena at ultrafast timescales. However, challenges such as the interfacial impedance mismatch, FM deposition-induced defect generation, and interface modification by interfacial coupling or hybridization can impede their functionalization for spin-orbitronics. In this work, we utilize insulating TiOx barrier layers (BLs) to modify the interfacial spin conductance structurally, disentangle spin pumping and magnetic proximity effects (MPE), and establish external control over ultrafast magnetization dynamics in single-layer graphene/TiOx/Co systems. All-optical time-resolved magneto-optical Kerr effect measurements of femtosecond to nanosecond spin dynamics reveal systematic tunability of ultrafast magnetic parameters via barrier engineering. The thickness-dependent damping modulation in Co indicates strong spin pumping, with interfacial spin transparency close to half its physical limit in the presence of an ultrathin BL, where MPE is eliminated. Our results show that appropriately chosen ultrathin BLs can prevent interfacial alterations from ferromagnetic metals, facilitating efficient spin detection in graphene and enhancing control over spin angular momentum dissipation in graphene/FM interfaces.