Time‐resolved K err‐effect and Spin Dynamics in Itinerant Ferromagnets

Abstract

The availability of femtosecond pulsed‐laser sources in combination with the development of time‐resolved and sensitive magneto‐optical schemes, have paved the way toward the exploration of the dynamics of spin systems at ultimate time scales. This chapter focuses on the exploration of subpicosecond processes in itinerant ferromagnet systems, which after a decade of research has now become an exciting and mature field of research. Both the potential and limitations of the experimental techniques, mostly concentrating on all‐optical approaches, and the subtle relation with processes being probed are being explained. The main part, though, is devoted to a review of experimental efforts and the physical insight that has emerged for the complementary spin‐dependent processes being investigated: populational dynamics (including state‐filling effects such as dichroic bleaching and direct transfer of angular momentum from the laser field), loss of magnetic order after laser heating, laser‐induced modification of anisotropy (including dynamics of exchange‐coupled systems)–triggering precessional phenomena, and the very recently discovered possibility to generate magnetic order at ultrafast timescales by driving metamagnetic phase transitions.

Nonlocal ultrafast demagnetization dynamics of Co/Pt multilayers by optical field enhancement

“…H(t) is the Heaviside function, and the time resolution of the experiment is taken into account by performing a convolution with a Gaussian G(t) with an FWHM of 180 fs. In passing we like to note that care has to taken when comparing extracted absolute de-and remagnetization time constants reported in the literature, as they will not only evidently depend on the phenomenological model used to describe the data [14], but also on the time range taken into account for fitting. In particular, slower remagnetization processes associated with heat diffusion can have a considerable influence on both τ re and τ , de in spite of being dominated by extrinsic properties like sample geometries and substrates.…”

Extension of Yafet's theory of spin relaxation to ferromagnets

“…At the moment the ultimately short timescale is achieved by driving the system to a strongly nonequilibrium regime with a strong femtosecond (fs) laser pulse, which induces a nearly complete loss of spin magnetic order in a hundred or a few hundred fs [1][2][3][4][5]. The mechanism of transfer of angular momentum from the spin system to other degrees of freedom on such a short timescale is still a matter of vivid discussions (see, e.g., the most recent publication [5]).…”

A non-linear dissipative model of magnetism

“…This discrepancy would deserve a deeper discussion, nevertheless we can assert that our approach brings a new theoretical scheme to investigate the dynamics of magnetic processes. Equation ( 5), which can be extended to several dissipative channels, should help to justify and parametrize the phenomenological models [20]. The model presented above opens also the way for more fundamental studies concerning the theoretical status and the formulation of irreversible thermodynamics, which is still an unachieved science.…”