Demonstration of on-chip all-optical switching of magnetization in integrated photonics

TL;DR

This paper demonstrates on-chip all-optical magnetization switching in a silicon nitride photonic circuit, achieving high contrast and deterministic control using femtosecond laser pulses, advancing integrated spintronic-photonic technologies.

Contribution

It introduces the first demonstration of single-pulse all-optical magnetization switching within a photonic integrated circuit, highlighting the importance of device scaling for robustness.

Findings

Achieved up to 90% switching contrast in 500 nm-wide devices.

Switching becomes stochastic in larger Hall crosses due to non-uniform absorption.

Finite-element simulations confirm the role of optical absorption and domain wall dynamics.

Abstract

Ultrafast all-optical magnetization switching (AOS) holds great promise for nextgeneration spintronic memory and hybrid spintronic-photonic systems. However, most implementations to date rely on bulky free-space optical setups, limiting scalability and practical integration. As a critical step toward integrated applications, we demonstrate single-pulse AOS within a silicon nitride (Si3N4) photonic integrated circuit. Using trains of femtosecond laser pulses guided through on-chip waveguides, we achieve deterministic toggle switching in a sub-micron out-of-plane Co/Gd Hall cross patterned directly atop the photonic waveguide. Electrical readout via the anomalous Hall effect reveals a switching contrast of up to 90% for 500 nm-wide devices. In larger Hall crosses, the contrast decreases and switching becomes stochastic, consistent with spatially non-uniform optical absorption as confirmed by finite-element simulations. This behavior is hypothetically attributed to domain wall relaxation and thermally assisted (de)pinning processes within partially switched regions. Our results highlight the critical role of device scaling in achieving robust on-chip AOS and establish a foundation for ultrafast, energy-efficient, and fully integrated spintronic-photonic platforms.