Intrinsic non-Markovian magnetisation dynamics

arXiv:2512.07378v2 Announce Type: replace Abstract: Memory effects are widespread in complex systems while evidence of non-Markovian dynamics in fundamental physical systems has been limited to specifically engineered cases. Here we report on the experimental observation of non-Markovian magnetisation dynamics in crystalline cobalt. Intense terahertz electromagnetic driving brings the system into a non-equilibrium state, and allows us to follow its magnetisation dynamics in real time at low temperatures. The response reveals a striking multi-peaked frequency spectrum that defies conventional descriptions. Using open quantum system theory we evidence that a non-Markovian memory kernel, arising from spin-phonon bath coupling, naturally explains both the spectral structure and its temperature dependence. Theoretical prediction of the spectrum is accomplished by simulating the non-Markovian Landau-Lifshitz-Gilbert equation, while analytics quantitatively determines the frequencies of three spectral peaks. The results demonstrate that intrinsic memory effects can emerge in a simple ferromagnet, opening new opportunities to explore and control non-Markovian dynamics in condensed-matter systems.