Regensburg 2019 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 2: Ultrafast magnetization effects and magnetization dynamics

MA 2.14: Vortrag

Montag, 1. April 2019, 13:00–13:15, H37

Effect of ultrashort laser pulse on the magnetic and chemical state of individual Co nanoparticles probed by X-PEEM — •Tatiana M. Savchenko, Michele Buzzi, Jaianth Vijayakumar, Martin Timm, Ludovic Howald, David Bracher, Carlos A. F. Vaz, Frithjof Nolting, and Armin Kleibert — Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen, Switzerland

The discovery of all-optical switching (AOS) in ferrimagnetic alloys such as FeGdCo using ultrashort laser pulses has stimulated immense activities in the field of magnetism. More recently, AOS was also observed in 3d transition metal thin film systems. In this work, we combine X-ray photoemission electron microscopy (X-PEEM) with X-ray magnetic circular dichroism (XMCD) and X-ray absorption spectroscopy (XAS) to observe the response of the magnetization and the chemical state of individual and well separated Co nanoparticles with sizes between 8 and 25 nm deposited on silicon wafers upon excitation with single 50 fs laser pulses with a wavelength of 800 nm. We find that the laser pulses with fluences up to about 7 mJ/cm2 have no noticeable effect on the magnetic state of the particles, irrespective of the laser polarization. At higher fluences, we find that the nanoparticles undergo a chemical reaction with the Si substrate and lose magnetic contrast. Calculations indicate that Rayleigh scattering significantly reduces the number of absorbed photons in a nanoparticle due to the large wavelength relative to its diameter. Thus, much higher laser fluences as compared to thin films together with laser transparent substrates are required to achieve all-optical switching in individual nanoparticles.

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