Where does the spin angular momentum go in laser induced demagnetisation?

Abstract

The dynamics of ultrafast demagnetisation in 3$d$ magnets is complicated by the presence of both spin $\check{S}$ and orbital $\check{L}$ angular momentum, with the microscopic mechanism by which the magnetic moment is redistributed to the lattice, and at what time scales, yet to be resolved. Employing state-of-the-art time dependent density function theory we disentangle the dynamics of these two momenta. Utilising ultra short (5~fs) pulses that separate spin-orbit (SO) and direct optical excitation time scales, we demonstrate a two-step microscopic mechanism: (i) an initial loss of $\check{L}$ due to laser excitation, followed post pulse by (ii) an increase of $\check{L}$ as $\check{S}$ transfers to $\check{L}$ during subsequent ($>15$~fs) SO induced spin-flip demagnetisation. We also show that to see an unambiguous transfer of $\check{S}$ to $\check{L}$ a short pulse is required.

arXiv comment5 pages 4 figures

References in corpus (8)

• Petahertz Spintronics
• The Ultrafast Einstein-De Haas Effect
• Many-body theory of ultrafast demagnetization and angular momentum transfer in ferromagnetic transition metals
• Role of Spin Flips versus Spin Transport in Non Thermal Electrons Excited by Ultrashort Optical Pulses in Transition Metals
• Dielectric response of laser-excited silicon
• Competing spin transfer and dissipation at Co/Cu(001) interfaces on femtosecond timescales
• Femtosecond x-ray absorption spectroscopy of spin and orbital angular momentum in photoexcited Ni films during ultrafast demagnetization
• X-ray circular dichroism versus orbital magnetization

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• Ultrafast optical generation of antiferromagnetic meron-antimeron pairs with conservation of topological charge
• Electronic origin of x-ray absorption peak shifts
• Strong ultrafast demagnetization due to the intraband transitions
• Ultrafast chiral precession of spin and orbital angular momentum induced by circularly polarized laser pulse
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• Photo-induced modification and relaxation dynamics of Weyl-semimetals
• Ultrafast Spin Injection in Graphene via Dynamical Carrier Filtering at Transition Metal Dichalcogenide Interfaces
• Interplay of electron-magnon scattering and spin-orbit induced electronic spin-flip scattering in a two-band Stoner model
• Femtosecond charge and spin dynamics in CoPt alloys
• Ultrafast magnetic moment transfer and bandgap renormalization in monolayer FeCl${}_2$