Robust Vertical Exchange Bias Modulates Spin Decoherence in 0D Core-Shell Nanoparticles.

Abstract

While recent advancements in spin manipulation have utilized topological insulators and non-collinear antiferromagnets confined to two-dimensional films, dimensional limitations have hindered the realization of truly freestanding spin-dependent quantum nanodevices (nm³). Here, we exploit a robust vertical exchange bias confined within core-shell FePt@MnO nanoparticles (<i>D</i> ∼ 9 nm) to control the spin decoherence time of Fe and Mn magnetic atoms. The magnitude (approximately 17% of interfacial spins are fully pinned) and robustness (the pinned spins remain stable even under a negative field of -5 T) of this anomalous exchange bias arise from a coherent interface where strain-induced lattice distortion displaces Mn cations by ångström-scale distances from their equilibrium positions, aligning them with Fe cations. This interfacial coherence enhances interfacial spin-spin exchange coupling─manifested as the anomalous exchange-bias effect─which directly modulates spin decoherence dynamics: τ₂ for Mn²⁺ spins shortens by 9.8% (108.3 ps → 98.5 ps), while Fe spins exhibit a concomitant τ₂ enhancement. This work establishes a direct link between spin decoherence time and the exchange-bias effect, offering a pathway for the coherent engineering of quantum nanomaterials.