An international team has succeeded at BESSY II for the first time to elucidate how ultrafast spin-polarised current pulses can be characterised by measuring the ultrafast demagnetisation in a magnetic layer system within the first hundreds of femtoseconds. The findings are useful for the development of spintronic devices that enable faster and more energy-efficient information processing and storage. The collaboration involved teams from the University of Strasbourg, HZB, Uppsala University and several other universities.
Spintronic components are not based on moving charges, but on changes in the orientation of magnetic moments, such as electron spins. Spin-current-based devices can therefore operate extremely quickly, currently on time scales of up to one hundred picoseconds (one picosecond is 10-12 s). However, the microscopic processes themselves run much faster, in the range of a few hundred femtoseconds (1 fs = 10-15 s).
Magnetic layers form a spin valve
Now, an international team led by Prof. Christine Boeglin, University of Strasbourg, has been able to experimentally observe some of these particularly interesting dynamic processes in a magnetic layer system for the first time. They investigated a so-called spin valve consisting of alternating layers of platinum-cobalt and an iron-gadolinium alloy layer. In this system, interactions between excited (hot) electrons and magnetic layers are particularly strong. First author Deeksha Gupta and her colleagues conducted the experiments at the femtoslicing station at BESSY II together with the HZB team that is operating this worldwide unique infrastructure.
With a femtosecond infrared laser (IR), they generated hot electrons (HE) in a platinum (Pt) top layer. A thick copper layer (Cu, 60 nm) ensures that only HE pulses reach the Co/Pt layer at the front of the spin valve, which acted as a spin polariser, generating spin-polarised HE pulses (SPHE).
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Image: The scheme shows (from left to right): Hot electrons generated by a laser in platinum (light blue), the copper (yellow) is used to block the laser pulse so that only the hot electrons propagate and transport a spin current through the magnetic spin valve structure of cobalt platinum (blue-brown) and iron gadolinium (green).
Credit: D. Gupta /HZB