Coherent magnetization rotation induced by optical modulation in ferromagnetic/antiferromagnetic exchange-coupled bilayers

TLDR

The study investigates magnetization switching dynamics in NiFe/NiO bilayers, examining how exchange bias amplitude influences coherent rotation. Femtosecond laser pulses transiently modulate the exchange bias field, providing the impulsive force that drives coherent magnetization dynamics. The dynamics agree with a Landau‑Lifshitz‑Gilbert model, and the damping constant shows a strong dependence on exchange bias. Published in Phys.

Abstract

We have demonstrated recently that ultrafast (\ensuremath{\sim}100 ps) coherent magnetization rotation can be induced by optical modulation of the exchange coupling in an exchange coupled bilayer (NiFe/NiO) with short laser pulses [Phys. Rev. Lett. 82, 3705 (1999)]. In this paper, we acquire further support of the coherent magnetization model by studying the details of magnetization switching dynamics, including the dependence on the amplitude of exchange bias field. The exchange bias field is subject to large transient modulation by femtosecond pulsed laser excitation, providing the impulsive force for subsequent magnetization dynamics. Good agreement is obtained with a simple model of coherent magnetization processes based on the Landau-Lifshitz-Gilbert equations of motion. We have also measured a strong dependence of the phenomenological damping constant (\ensuremath{\alpha}) on the exchange bias in the coupled ferromagnetic/antiferromagnetic spin system.