Spin-orbit torque-mediated spin-wave excitation as an alternative paradigm for femtomagnetism

TL;DR

This paper introduces a novel paradigm for femtomagnetism based on laser-induced spin-orbit torque, which efficiently explains ultrafast demagnetization by generating extensive spin waves within 20 femtoseconds.

Contribution

It demonstrates that augmenting traditional spin-wave theory with laser-induced spin-orbit torque explains rapid demagnetization, offering an alternative to existing mechanisms.

Findings

Massive spin waves generated across hundreds of lattice sites.

Collapse of long-range spin-spin correlation within 20 fs.

Provides explanation for recent experimental observations.

Abstract

Laser-induced femtosecond demagnetization, femtomagnetism, offers a potential route to develop faster magnetic storage devices. It is generally believed that the traditional spin-wave theory, which is developed for thermally driven slow demagnetization, can not explain this rapid demagnetization by design. Here we show that this traditional spin-wave theory, once augmented by laser-induced spin-orbit torque, provides a highly efficient paradigm for demagnetization, by capturing low-energy spin-wave excitation that is absent in existing mechanisms. Our paradigm is different from existing ones, but does not exclude them. Microscopically, we find that optical spin-orbit torque generates massive spin waves across several hundred lattice sites, collapsing the long-range spin-spin correlation within 20 fs. Our finding does not only explain new experiments, but also establishes an alternative paradigm for femtomagnetism. It is expected to have far-reaching impacts on future research.