Ultrafast Demagnetization through Femtosecond Generation of Non-thermal Magnons

Abstract

Ultrafast laser excitation of ferromagnetic metals gives rise to correlated, highly non-equilibrium dynamics of electrons, spins and lattice, which are, however, poorly described by the widely-used three-temperature model (3TM). Here, we develop a fully ab-initio parameterized out-of-equilibrium theory based on a quantum kinetic approach--termed (N+2) temperature model--that describes magnon occupation dynamics due to electron-magnon scattering. We apply this model to perform quantitative simulations on the ultrafast, laser-induced generation of magnons in iron and demonstrate that on these timescales the magnon distribution is non-thermal: predominantly high-energy magnons are created, while the magnon occupation close to the center of the Brillouin zone even decreases, due to a repopulation towards higher energy states via a so-far-overlooked scattering term. We demonstrate that the simple relation between magnetization and temperature computed at equilibrium does not hold in the ultrafast regime and that the 3TM greatly overestimates the demagnetization. The ensuing Gilbert damping becomes strongly magnon wavevector dependent and requires a description beyond the conventional Landau-Lifshitz-Gilbert spin dynamics. Our ab-initio-parameterized calculations show that ultrafast generation of non-thermal magnons provides a sizable demagnetization within 200fs in excellent comparison with experimentally observed laser-induced demagnetizations. Our investigation emphasizes the importance of non-thermal magnon excitations for the ultrafast demagnetization process.

References in corpus (18)

• Super-Diffusive Spin-Transport as a Mechanism of Ultrafast Demagnetization
• Identification of the dominant precession damping mechanism in Fe, Co, and Ni by first-principles calculations
• Polarized phonons carry the missing angular momentum in femtosecond demagnetization
• Theory of Out-of-Equilibrium Ultrafast Relaxation Dynamics in Metals
• Low relaxation rate in a low-Z alloy of iron
• Interatomic exchange coupling of BCC iron
• Reinventing atomistic magnetic simulations with spin-orbit coupling
• Spin-lattice couplings in two-dimensional CrI${}_3$ from first-principles study
• Lattice dynamics and ultrafast energy flow between electrons, spins, and phonons in a 3d ferromagnet
• $s$-$d$ model for local and nonlocal spin dynamics in laser-excited magnetic heterostructures
• Modeling coupled spin and lattice dynamics
• Modeling ultrafast demagnetization and spin transport: the interplay of spin-polarized electrons and thermal magnons
• Intrinsic energy flow in laser-excited 3$d$ ferromagnets
• Influence of non-local damping on magnon properties of ferromagnets
• Ultrafast magnetization reversal in ferromagnetic spin-valves: an s-d model perspective
• Electron-phonon mediated spin-flip as driving mechanism for ultrafast magnetization dynamics in 3$d$ ferromagnets
• Rotationally invariant formulation of spin-lattice coupling in multi-scale modeling
• Nonequilibrium magnons from hot electrons in antiferromagnetic systems

Cited by in corpus (7)

• Ultrafast demagnetization in ferromagnetic materials: Origins and progress
• Origins of electromagnetic radiation from spintronic terahertz emitters: A time-dependent density functional theory plus Jefimenko equations approach
• Charge and spin current pumping by ultrafast demagnetization dynamics
• Ultrafast electron dynamics in altermagnetic materials
• Generation of Phonons with Angular Momentum During Ultrafast Demagnetization
• Non-thermal electrons open the non-equilibrium pathway of the phase transition in FeRh
• Interplay of electron-magnon scattering and spin-orbit induced electronic spin-flip scattering in a two-band Stoner model