Daniel Marko, Henry Han, Wan-Chen Chuang, Jiann-Yeu Chen, Fernando Valdés-Bango García, John-Ching Wu, Ko-Wei Lin, Luis Manuel Álvarez-Prado, David Schmool
Characterizing the dynamic magnetic properties of nanoscale magnetic thin films, multilayers, and nanostructures is crucial for exploiting their potential for practical applications such as in logic and microwave devices operating in the GHz region. Among the various techniques suitable for high-frequency characterization, ferromagnetic resonance spectroscopy (FMR) is widely considered as one of the gold standards. In its most advanced version, broadband vector network analyzer (VNA) FMR, it represents the perfect tool for detailed and accurate analysis of magnetic damping processes. In the first part of this talk, a compact introduction to FMR including underlying physics as well as technical details will be given, followed by a short presentation of a recently built VNA-FMR setup at UVSQ. In the second and longer part, both static and dynamic magnetic properties of two selected material systems will be discussed in depth, with focus on data obtained from VNA-FMR measurements. The first study involves Fe/Ag continuous films and nanodot arrays of various sizes prepared for elucidating the mechanisms of a potentially existing magneto-plasmonic coupling. The second sample system consisting of trilayers of Py/Al/NdCo is investigated with support from micromagnetic simulations with the purpose of studying the influence of competing anisotropies, in-plane for Permalloy (Py) and out-of-plane for NdCo, on its magnetic properties.
Time resolution limited dynamic measurements show the need for improved techniques to access ultrafast demagnetisation processes on the sub-10 femtosecond timescale. We have constructed a state-of- the-art time-resolved magneto-optic Kerr effect (TR-MOKE) apparatus for the observation of ultrafast demagnetization and precessional dynamics in ferromagnetic materials. Our system can operate well below the current ranges used by most researchers (typically in the region of 40 fs). Using current ultrafast optical methods of pulse compression, designed to obtain unprecedented temporal resolution, we have developed a dual-colour pump-probe technique: This enables us to attain an ultimate resolution in the 12 fs range, the spectral range being split between pump and probe beams. We have demonstrated that the system has the capacity for ultrafast demagnetization measurements using a GdFeCo thin film. Future developments will employ the full spectral range in both pump and probe branches to reach an expected temporal resolution in the vicinity of 6 fs, corresponding to few-cycle pulses.
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