Laser-induced ultrafast demagnetization in the presence of a nanoscale magnetic domain network

Abstract

Femtosecond magnetization phenomena have been challenging our understanding for over a decade. most experiments have relied on infrared femtosecond lasers, limiting the spatial resolution to a few micrometres. With the advent of femtosecond X-ray sources, nanometric resolution can now be reached, which matches key length scales in femtomagnetism such as the travelling length of excited 'hot' electrons on a femtosecond timescale. Here we study laser-induced ultrafast demagnetization in [Co/Pd] 30 multilayer films, which, for the first time, achieves a spatial resolution better than 100 nm by using femtosecond soft X-ray pulses. This allows us to follow the femtosecond demagnetization process in a magnetic system consisting of alternating nanometric domains of opposite magnetization. no modification of the magnetic structure is observed, but, in comparison with uniformly magnetized systems of similar composition, we find a significantly faster demagnetization time. We argue that this may be caused by direct transfer of spin angular momentum between neighbouring domains.

Testing spin-flip scattering as a possible mechanism of ultrafast demagnetization in ordered magnetic alloys

“…Element specific probes [13][14][15] as well as systematic studies using more conventional time resolved techniques [16] on ultrashort time scales have had a tremendous share in the advancement of knowledge in this particular field. For example, for ferrimagnetic 3d-transition metal / 4f-rare earth alloys (3d-4f) such as CoFeGd used for all-optical switching, that a transient ferromagnetic state exists in the process of ultrafast magnetization reversal [17].…”

Generation of circularly polarized radiation from a compact plasma-based extreme ultraviolet light source for tabletop X-ray magnetic circular dichroism studies

“…25,26 The latter property renders Co/Pt multilayer films an ideal model system for studies of laser heating effects on the ferromagnetic domain structure employing high harmonics 27 as well as for studies of femtosecond magnetization dynamics of nanometer scale domains with a freeelectron laser. 28,29 The magnetization curve of the Co/Pt multilayer sample measured with polar magneto-optical Kerr effect (P-MOKE) is shown in the inset of Fig. 7.…”

Imaging instantaneous electron flow with ultrafast resonant x-ray scattering

“…Resonant conditions are also essential for magnetic scattering, since magnetic interactions with light are very weak [24]. Time-resolved diffraction by resonant x-ray pulses has been used to reveal various ultrafast phenomena, such as melting of orbital and spin orders in strongly correlated materials [25,26], laser-induced spin reversal [27], and demagnetization [28]. Applications to coherent electron dynamics have not yet been reported.…”