title: Damped precession of the magnetization vector of superparamagnetic nanoparticles excited by femtosecond optical pulses.
abstract: The ultrafast magnetization and electron dynamics of superparamagnetic cobalt nanoparticles, embedded in a dielectric matrix, have been investigated using femtosecond optical pulses. Our experimental approach allows us to bypass the superparamagnetic thermal fluctuations and to observe the trajectory of the magnetization vector which exhibits a strongly damped precession motion. The magnetization precession is damped faster in the superparamagnetic particles than in cobalt films or when the particle size decreases, suggesting that the damping is enhanced at the metal dielectric interface. Our observations question the gyroscopic nature of the magnetization pathway when superparamagnetic fluctuations take place as we discuss in the context of Brown's model.
authors.affiliation: Institut de Physique et Chimie des Matériaux de Strasbourg, (UMR 7504 CNRS-ULP), Strasbourg 67034, France.
authors.forename: L H F
authors.initials: LH
authors.lastname: Andrade
authors.forename: A
authors.initials: A
authors.lastname: Laraoui
authors.forename: M
authors.initials: M
authors.lastname: Vomir
authors.forename: D
authors.initials: D
authors.lastname: Muller
authors.forename: J-P
authors.initials: JP
authors.lastname: Stoquert
authors.forename: C
authors.initials: C
authors.lastname: Estournès
authors.forename: E
authors.initials: E
authors.lastname: Beaurepaire
authors.forename: J-Y
authors.initials: JY
authors.lastname: Bigot