4.3 Nanoscale Samples and Integrated Optics
Project coordinators: A. Mermillod-Blondin , W. EngelTopic 2: Functional magnetic layer systems
Another central topic area is the investigation of ultrafast magnetization dynamics, in particular laser-driven spin and electron transport. Here, experiment-specific thin films and multilayers play a decisive role. Tailored ferrimagnetic alloys enabling purely optical magnetization switching, or ferromagnetic multilayers optimized via He-ion implantation to nucleate skyrmion ensembles and bags, provide model systems to probe fundamental mechanisms under ultrafast excitation. The iterative feedback loop between time-resolved measurements and sample optimization ensures rapid progress and systematic refinement of material properties.
Example 1: Ferromagnetic systems
Customised sample systems are developed and manufactured primarily for in-house experiments in various MBI projects. For example, ferromagnetic thin-film and multi-layer systems are grown to investigate the influence of magnetic and chemical inhomogenities in the nanoscale on ultrafast spin dynamics and ultrafast magnetic switching.
Depending on the materials and layer compositions used, layer systems with different magnetic properties are obtained, e.g. visible in the formation of domains of different sizes.
Example 2: Skyrmions
Several ferromagnetic layer systems, such as MgO/CoFeB/Pt-based multilayers, exhibit a perpendicular magnetic anisotropy, which enables the generation of skyrmions.
The precise modification of the local magnetic anisotropy in the nanometre range, achieved in combination with a He+-FIB, enables the deterministic nucleation of skyrmions and skyrmion bags due to ultrashort laser pulses.
Example 3: Ferrimagnetic systems
Ultrathin alloys, consisting of a rare earth transition metal like GdCo, show a large perpendicular magnetic anisotropy supporting the so called all-optical helicity-independent switching (AO-HIS) of the magnetization state in these alloys, which is understood by different demagnetization dynamics of the two antiferromagnetically coupled spin sub-lattices.
We observe localized AO-HIS down to a critical dimension of 240 nm after excitation of the gold nanostructures by a single 370 fs long laser pulse with a centre wavelength of 1030 nm.