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3.2 Solids and Nanostructures: Electrons, Spins, and Phonons
Project coordinator(s): C. von Korff Schmising, M. Wörner
Topics

T4: Magnetism and transient electronic structure

 

Introduction

We aim to understand how fundamental interactions in magnetism like spin-orbit coupling, exchange interaction and spin dependent electron transport allow the optical manipulation of magnetic order on an ultrafast time scale. Currently we focus on ferromagnetic and ferrimagnetic metallic thin films and multilayers and explore the influence of magnetic and chemical nanoscale inhomogeneities on ultrafast spin dynamics and ultrafast magnetic switching. Furthermore, we design and manufacture plasmonic structures for subwavelength confinement of the optical excitation to achieve control of magnetism on the nanoscale.

In addition to all-optical spectroscopy we use novel light sources like free electron laser and high harmonic sources in the extreme ultraviolet spectral range to probe the transient magnetic state via element-specific magnetic dichroic spectroscopy and small angle scattering. These experimental methods give us detailed information on the distinct dynamics in multicomponent magnetic systems with a femtosecond temporal and nanometre spatial resolution.

Figure 1: Schematic of the experimental setups for magnetic small angle scattering and magnetic dichroism spectroscopy. The extreme ultraviolett probe pules are derived by free-electron laser or high harmonic radiation.

 

Ultrafast Interface Magnetism of Co/Pt Heterostructures

Interface effects have very recently been identified to play a decisive role in ultrafast spin dynamics and all-optical magnetic switching. Currently discussed mechanism include interface exchange interaction, enhanced spin-orbit coupling, spin-polarized electron transport across an interface and more generally phenomena arising from symmetry breaking at the boundary.

However, progress in understanding and, hence, in the successful design of layered multicomponent magnetic systems for ultrafast applications has been challenged by the difficulty to experimentally access the underlying complex microscopic processes. Our novel approach of time- resolved magnetic circular dichroism combines femtosecond time resolution with element-specificity, both a prerequisite for extracting information about contributions of the different materials and interacting spin systems.

In the present work, we demonstrated for the first time time resolved magnetic dichroic measurements with broad-band high harmonic radiation and show simultaneous sensitivity to a Co film and the Co/Pt interface in a single experiment.

Figure 2: (a) Inset: x-ray absorption (XAS) and magnetic circular dichroism (MCD) of a Pt/Co/Pt trilayer. Pronounced magnetic signals are found at the Co M2,3 edge and O2,3 and N6,7 edge of Pt. High harmonic spectrum showing resonant magnetic asymmetry at 60.8 eV and 54.6 eV, which we can attribute to Co and Pt, respectively. (b) Ultrafast evolution of Co and Pt suggesting that the Co/Pt interface directly follows the magnetization dynamics of the Co film.

Collaboration with N. Zhavoronkov, O. Kornilov and M.J.J. Vrakking.

Physical Review B 92, 220405(R) (2015)

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