Role of Oxygen Coordination on the Ultrafast Demagnetization in Ferrite Nanoparticles
E. Terrier, Y. Liu, S. Begin, B. Pichon, J.-Y. Bigot and V. Halte
Institut de Physique et de Chimie des Matériaux de Strasbourg, UMR7504, CNRS et Université de Strasbourg, 23 rue du Loess, 67034 Strasbourg, France
Full Text PDF
In this work, we have studied the ultrafast dynamics of charges and spins in assemblies of magnetite (Fe3O4) and maghemite (γ -Fe2O3) nanoparticles. We demonstrate that using time-resolved magneto-optics one is able to disentangle those very similar iron oxide structures. The Fe3O4 nanoparticles are elaborated by hydrothermal decomposition and deposited by drop on a glass substrate. γ -Fe2O3 nanoparticles assemblies have been obtained by annealing the Fe3O4 nanoparticles. Comparing time resolved transmission and Faraday rotation, our measurements show that in case of Fe3O4 the demagnetization occurs after the thermalization of the charges, as expected from previous works on ultrafast quenching of magnetization in ferromagnetic nanostructures. On the contrary, in the case of maghemite nanoparticles, an acceleration of the demagnetizing occurs, leading to a simultaneous charges and spins dynamics. We attribute this behavior to the rearrangement of vacancies and annealing of crystal defects in maghemite.

DOI: 10.12693/APhysPolA.127.345
PACS numbers: 78.47.J-, 78.20.Ls, 75.30.Et, 75.75.Fk