Two types of all-optical magnetization switching mechanisms using femtosecond laser pulses

TLDR

Magnetization can be switched in thin films by ultrashort polarized laser pulses, with both helicity‑dependent and helicity‑independent mechanisms observed in GdFeCo and other ferrimagnetic, ferromagnetic, and granular materials, challenging the uniqueness of the underlying microscopic origin. The study aims to distinguish two all‑optical switching mechanisms—a single‑pulse process and a cumulative process—and to investigate their microscopic origins. We probe the switching in ferrimagnetic and ferromagnetic Hall crosses using time‑resolved anomalous Hall effect measurements, enabling an all‑electrical, time‑dependent investigation of the processes on different timescales. The cumulative switching is a two‑step mechanism consisting of heat‑driven demagnetization followed by helicity‑dependent remagnetization.

Abstract

Magnetization manipulation in the absence of an external magnetic field is a topic of great interest, since many novel physical phenomena need to be understood and promising new applications can be imagined. Cutting-edge experiments have shown the capability to switch the magnetization of magnetic thin films using ultrashort polarized laser pulses. In 2007, it was first observed that the magnetization switching for GdFeCo alloy thin films was helicity-dependent and later helicity-independent switching was also demonstrated on the same material. Recently, all-optical switching has also been discovered for a much larger variety of magnetic materials (ferrimagnetic, ferromagnetic films and granular nanostructures), where the theoretical models explaining the switching in GdFeCo films do not appear to apply, thus questioning the uniqueness of the microscopic origin of all-optical switching. Here, we show that two different all-optical switching mechanisms can be distinguished; a "single pulse" switching and a "cumulative" switching process whose rich microscopic origin is discussed. We demonstrate that the latter is a two-step mechanism; a heat-driven demagnetization followed by a helicity-dependent remagnetization. This is achieved by an all-electrical and time-dependent investigation of the all-optical switching in ferrimagnetic and ferromagnetic Hall crosses via the anomalous Hall effect, enabling to probe the all-optical switching on different timescales.