Analysis of the time-resolved magneto-optical Kerr effect for ultrafast magnetization dynamics in ferromagnetic thin films

TLDR

Laser‑induced ultrafast demagnetization is probed by the time‑resolved magneto‑optical Kerr effect (MOKE). The study demonstrates how to disentangle pump‑induced variations of magnetization and magneto‑optical coefficients in thin Fe films on MgO, and provides a mathematical formalism for retrieving genuine laser‑induced magnetization dynamics applicable to real experiments. The authors investigate thin Fe films on MgO without electronic transport, emphasizing that high temporal resolution and simultaneous measurement of MOKE rotation and ellipticity are essential for accurately assessing sub‑picosecond magnetization dynamics. The developed framework clarifies the time‑resolved MOKE technique and enhances understanding of the interplay between ultrafast laser‑induced optical and magnetic effects.

Abstract

We discuss fundamental aspects of laser-induced ultrafast demagnetization probed by the time-resolved magneto-optical Kerr effect (MOKE). Studying thin Fe films on MgO substrate in the absence of electronic transport, we demonstrate how to disentangle pump-induced variations of magnetization and magneto-optical coefficients. We provide a mathematical formalism for retrieving genuine laser-induced magnetization dynamics and discuss its applicability in real experimental situations. We further stress the importance of temporal resolution achieved in the experiments and argue that measurements of both time-resolved MOKE rotation and ellipticity are needed for the correct assessment of magnetization dynamics on sub-picosecond timescales. The framework developed here sheds light onto the details of the time-resolved MOKE technique and contributes to the understanding of the interplay between ultrafast laser-induced optical and magnetic effects.