Laser-induced ultrafast transport and demagnetization at the earliest time: First-principles and real-time investigation

Abstract

Here we carry out a first-principles time-dependent calculation to investigate how fast electrons actually move under laser excitation and how large the electron transport affects demagnetization on the shortest time scale. To take into account the transport effect, we implement the intraband transition in our theory. In the bulk fcc Ni, we find the effect of the spin transport on the demagnetization is extremely small, no more than 1\%. The collective electron velocity in Ni is 0.4 $\mathring{\mathrm{A}}/fs$, much smaller than the Fermi velocity, and the collective displacement is no more than 0.1 $\mathring{\mathrm{A}}$. But this does not mean that electrons do not travel fast; instead we find that electron velocities at two opposite crystal momenta cancel each other. We follow the $\Gamma$-X line and find a huge dispersion in the velocities in the crystal momentum space. In the Fe/W(110) thin film, the overall demagnetization is larger than Ni, and the Fermi velocity is higher than Ni. However, the effect of the spin transport is still small in the Fe/W(110) thin film. Based on our numerical results and existing experimental findings, we propose a different mechanism that can explain two latest experimental results. Our finding sheds new light on the effect of ballistic transport on demagnetization.

arXiv comment32 pages, 6 figures, (accepted for publication in Journal of Physics: Condensed Matter (2018))

References in corpus (12)

• Super-Diffusive Spin-Transport as a Mechanism of Ultrafast Demagnetization
• Ultrafast transport of laser-excited spin polarized carriers in Au/Fe/MgO(001)
• High harmonic generation in undoped graphene: Interplay of inter- and intraband dynamics
• Terahertz spectroscopy for all-optical spintronic characterization of the spin-Hall-effect metals Pt, W and Cu${}_{80}$Ir${}_{20}$
• Electron-phonon-scattering dynamics in ferromagnetic metals and its influence on ultrafast demagnetization processes
• Role of Spin Flips versus Spin Transport in Non Thermal Electrons Excited by Ultrashort Optical Pulses in Transition Metals
• Competing spin transfer and dissipation at Co/Cu(001) interfaces on femtosecond timescales
• Ultrafast demagnetization in bulk vs thin films: an ab-initio study
• Laser induced THz emission from femtosecond photocurrents in Co/ZnO/Pt and Co/Cu/Pt multilayers
• Resolving photon-shortage mystery in femtosecond magnetism
• Magnetization dynamics and damping due to electron-phonon scattering in a ferrimagnetic exchange model
• Ultrafast hot-electron induced quenching of Tb4f magnetic order

Cited by in corpus (6)

• Probing optical spin-currents using THz spin-waves in noncollinear magnetic bilayers
• Laser-induced ultrafast demagnetization and perpendicular magnetic anisotropy reduction in a Co${}_{88}$Tb${}_{12}$ thin film with stripe domains
• Strain-induced Shape Anisotropy in Antiferromagnetic Structures
• Simultaneous two-color snapshot view on ultrafast charge and spin dynamics in a Fe-Cu-Ni tri-layer
• Spin-orbit torque-mediated spin-wave excitation as an alternative paradigm for femtomagnetism
• Spin Berry points as crucial for ultrafast demagnetization