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Séminaire Magnétisme et Physique du spin de l’INSP

Role of electron motion in ultrafast demagnetization - B. Vodungbo - Mardi 10 novembre 2015 à 11 h

INSP - 4 place Jussieu - 75252 PARIS Cedex 05 - Barre 22-32 - 2e étage, salle 201

B. Vodungbo - LCPMR - Sorbonne universités - UPMC

Abstract

Ultrafast demagnetization refers to a rapid loss of magnetization ( 100 fs) upon excitation of a ferromagnetic thin film by an intense femtosecond laser pulse. Although several theoretical models have been proposed to explain this phenomenon, the available experimental data do not allow deciding among them. In particular, the intriguing prediction that superdiffusive spin transport could account for part or even all of the demagnetization observed has to be studied carefully in the light of recent contradictory results.

Using the key strengths of soft X-ray FEL sources (brightness, short wavelengths, femtosecond pulse duration, element selectivity), we have studied ultrafast demagnetization in Co based multilayers exhibiting a nanometric magnetic domain structure. Our FLASH experiment [1] gave evidence that ultrafast spin transport may alter the domain wall region. Using a refined experimental design at LCLS (march 2014) allowed us to confirm that superdiffusive spin transport between metallic and magnetic layers and between neighboring domains plays a role in ultrafast demagnetization, although purely local ultrafast quenching of magnetization can in some cases be observed, too.

In this presentation we will also compare these results with those that we have obtained with a table-top HHG source [2] and discuss the complementarity and advantages of both sources.

[1] Pfau B. et al. Nat. Commun. 3 1100 (2012).
[2] Vodungbo B. et al. Nat. Commun. 3 999 (2012).