Investigation of Ultrafast Demagnetization and Gilbert Damping and their Correlation in Different Ferromagnetic Thin Films Grown Under Identical Conditions

TL;DR

This study compares ultrafast demagnetization and damping in cobalt, nickel, and permalloy thin films using models and experiments, revealing how material properties influence magnetization dynamics under laser excitation.

Contribution

It provides a comparative analysis of demagnetization in different ferromagnetic films using 3TM and M3TM models, highlighting the role of material properties and fluence dependence.

Findings

Demagnetization time correlates with the Curie temperature to magnetic moment ratio.

Damping factors and demagnetization times are sensitive to the density of states at the Fermi level.

Numerical simulations estimate spin flip scattering probabilities and reservoir coupling parameters.

Abstract

Following the demonstration of laser-induced ultrafast demagnetization in ferromagnetic nickel, several theoretical and phenomenological propositions have sought to uncover its underlying physics. In this work we revisit the three temperature model (3TM) and the microscopic three temperature model (M3TM) to perform a comparative analysis of ultrafast demagnetization in 20-nm-thick cobalt, nickel and permalloy thin films measured using an all-optical pump-probe technique. In addition to the ultrafast dynamics at the femtosecond timescales, the nanosecond magnetization precession and damping are recorded at various pump excitation fluences revealing a fluence-dependent enhancement in both the demagnetization times and the damping factors. We confirm that the Curie temperature to magnetic moment ratio of a given system acts as a figure of merit for the demagnetization time, while the demagnetization times and damping factors show an apparent sensitivity to the density of states at the Fermi level for a given system. Further, from numerical simulations of the ultrafast demagnetization based on both the 3TM and the M3TM, we extract the reservoir coupling parameters that best reproduce the experimental data and estimate the value of the spin flip scattering probability for each system. We discuss how the fluence-dependence of inter-reservoir coupling parameters so extracted may reflect a role played by nonthermal electrons in the magnetization dynamics at low laser fluences.