Femtosecond laser-induced relaxation dynamics in ferromagnetic films

Studying the interaction between light and matter is a fundamental and powerful approach for physicists to probe the microcosmic world. Recent advancements in ultrafast optics, particularly the development of femtosecond laser pulses, have enabled the study of these interactions on unprecedented timescales. This has propelled research into ultrafast spin dynamics within magnetic materials, a central focus in modern condensed matter physics with direct implications for the advancement of spintronic technologies. This review provides a comprehensive discussion of ultrafast electron relaxation dynamics in magnetic materials as investigated via femtosecond laser pump-probe spectroscopy. This powerful technique serves as the primary methodological foundation for the discussed research, allowing for direct temporal observation of non-equilibrium states following laser excitation. We synthesize and examine the substantial body of related international and domestic research progress, detailing the characteristic timescales and pathways of energy dissipation following optical excitation. Furthermore, the review critically assesses the various proposed microscopic mechanisms that seek to explain these ultrafast processes, including models involving electron–electron scattering, electron–phonon coupling, and spin–lattice interactions. By consolidating empirical findings with theoretical frameworks, this work aims to clarify the current understanding of the fundamental processes governing ultrafast demagnetization and subsequent relaxation. The critical discussion presented herein not only consolidate the current understanding of ultrafast electron relaxation in laser-excited magnetic materials but also provide valuable insights and guidance for future investigations in this rapidly evolving field, which is of great significance for promoting the practical application of spintronic devices and advancing the frontier of condensed matter physics research.