X-ray laser FLASH uncovers fast demagnetization process
Magnetic force microscope image of a 10 by 10 micron sample
showing the magnetic domains' labyrinthine structure.
© Bastian Pfau
With the help of free-electron laser FLASH at the Helmholtz Research Centre DESY, an international team of researchers has recently described a most surprising effect that can result in faster demagnetization in ferromagnetic materials. This effect could be key to the continued miniaturization and acceleration of magnetic storage. Now, Prof. Dr. Stefan Eisebitt of the Helmholtz Zentrum Berlin (HZB) and TU Berlin and his team have published their findings in the current issue of the scientific journal Nature Communications (DOI 10.1038/ ncomms2108).
"The ability of a light pulse to effect localized changes to a material's magnetization is a well-known fact, but not until now have we been able to more closely observe the process, which has led to the discovery of a new mechanism," explains Stefan Eisebitt. This is because most ferromagnetic materials consist of a number of individual, differently oriented magnetic domains. "When bombarded with laser light, free electrons rush through the material, moving from one domain into an oppositely magnetized domain. These electrons carry part of the magnetization through the sample and are thus able to destroy the localized magnetization," explains TU Berlin's Bastian Pfau, junior researcher and the study’s primary author.
The TU Berlin, HZB, and DESY researchers along with their colleagues from the Universities of Hamburg and Paris, and from six other research institutes including SLAC – the Stanford Linear Accelerator Center in the US – all conducted their experiments at DESY's Hamburg-based free-electron laser FLASH. Previously, they had characterized the domain patterns at HZB's own synchrotron radiation source BESSY II and at Paris-based SOLEIL where they examined samples obtained from cobalt-platinum thin films whose nanoscale magnetic domains form labyrinthine structures. "Our results further demonstrate that the position and density of magnetic domain boundaries can influence demagnetization behavior," explains Stefan Eisebitt. "Our work has set the stage for a new approach to developing faster and smaller-sized magnetic storage specifically by building magnetic nanostructures."
- Spintronics at BESSY II: Real-time analysis of magnetic bilayer systemsSpintronic devices enable data processing with significantly lower energy consumption. They are based on the interaction between ferromagnetic and antiferromagnetic layers. Now, a team from Freie Universität Berlin, HZB and Uppsala University has succeeded in tracking, for each layer separately, how the magnetic order changes after a short laser pulse has excited the system. They were also able to identify the main cause of the loss of antiferromagnetic order in the oxide layer: the excitation is transported from the hot electrons in the ferromagnetic metal to the spins in the antiferromagnet.
- Element cobalt exhibits surprising propertiesThe element cobalt is considered a typical ferromagnet with no further secrets. However, an international team led by HZB researcher Dr. Jaime Sánchez-Barriga has now uncovered complex topological features in its electronic structure. Spin-resolved measurements of the band structure (spin-ARPES) at BESSY II revealed entangled energy bands that cross each other along extended paths in specific crystallographic directions, even at room temperature. As a result, cobalt can be considered as a highly tunable and unexpectedly rich topological platform, opening new perspectives for exploiting magnetic topological states in future information technologies.
- BESSY II: Insight into ultrafast spin processes with femtoslicingAn 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.