Abstract
When exciting a ferromagnetic film with a femtosecond optical laser pulse, then there is a partial demagnetization within a few hundred fs. This means that the angular momentum of the electronic system is transferred to the lattice. This transfer is calculated by describing the lattice degrees of freedom as spin-phonon eigenmodes which have a sharp angular momentum. Possible other lattice degrees of freedom are mentioned but not considered explicitly. For Ni and Fe the calculated amount of transfer of angular momentum to the spin-phonon eigenmodes is rather small.
Highlights
When a ferromagnetic film is excited by a laser pulse of length of 30–100 fs, the sample is partially demagnetized within a few hundred fs with a following remagnetization on a longer time scale [1, 2]
We cannot expect a perfect agreement between our theoretical values and the experimental values because we considered from the various contributions to ultrafast demagnetization just the contributions of spin-flip scatterings of electrons at spin-phonons
We have calculated for Ni and Fe the transfer of angular momentum from the spin system to the lattice after excitation of the system with a fs optical laser pulse
Summary
When a ferromagnetic film is excited by a laser pulse of length of 30–100 fs, the sample is partially demagnetized within a few hundred fs with a following remagnetization on a longer time scale [1, 2] It has been discussed both theoretically [3, 4] and experimentally [5]. In isotropic systems like amorphous materials, the degeneracy is given for arbitrary q, and it is possible to generate stationary phonon states with well-defined angular momentum [15] This does not help to describe the angular momentum transfer during demagnetization experiments which are mainly performed for crystalline ferromagnetic films. Within the framework of an electron-spin-phonon scattering Hamiltonian, we calculate for the first time explicitly the transfer of angular momentum from the electronic system to the lattice during ultrafast demagnetization
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