Ultrafast Spin Manipulation at THz frequencies
An ultrafast spin current triggers the emission of Terahertz-Radiation. © H. D. Wöhrle/Universität Göttingen
The demands for ever increasing speed of information storage and data processing have triggered an intense search for finding the ultimately fast ways to manipulate spins in a magnetic medium. In this context, the use of femtosecond light pulses – the fastest man-made event - with photon energies ranging from X-rays (as used for instance at the HZB femto-slicing facility) to THz spectral range proved to be an indispensable tool in ultrafast spin and magnetization dynamics studies.
In a paper in Nature Nanotechnology, HZB-scientist Ilie Radu and his colleagues from Fritz-Haber-Institut Berlin, Uppsala, Göttingen and Forschungzentrum Jülich demonstrate a simple but very powerful way of manipulating the spins at unprecedented speeds within the so far unexplored THz range (1THz=1012 Hz). They use a femtosecond laser pulse to photo-excite the spins from a magnetic material to a non-magnetic one that is chosen to either trap or release the electrons carrying the spins. By this method they are able to generate ultrashort spin currents with tailor-made shapes and durations, which are detected using an ‘ultrafast amperemeter’ (based on the Inverse Spin Hall Effect) that converts the spin flow into a terahertz electromagnetic pulse.
These findings will possibly allow us to develop and design novel material with tailor-made characteristics, which might boost the magnetic recording rates of the magnetic bits to unprecedented speeds at THz frequencies.
I.R.
The work is published in:T. Kampfrath et al. „Terahertz spin current pulses controlled by magnetic heterostructures”, Nature Nanotechnology 2013, doi: http://dx.doi.org/10.1038/NNANO.2013.43.
- BESSY II: Phosphorous chains – a 1D material with 1D electronic propertiesFor the first time, a team at BESSY II has succeeded in demonstrating the one-dimensional electronic properties of a material through a highly refined experimental process. The samples consisted of short chains of phosphorus atoms that self-organise at specific angles on a silver substrate. Through sophisticated analysis, the team was able to disentangle the contributions of these differently aligned chains. This revealed that the electronic properties of each chain are indeed one-dimensional. Calculations predict an exciting phase transition to be expected as soon as these chains are more closely packed. While material consisting of individual chains with longer distances is semiconducting, a very dense chain structure would be metallic.
- What vibrating molecules might reveal about cell biologyInfrared vibrational spectroscopy at BESSY II can be used to create high-resolution maps of molecules inside live cells and cell organelles in native aqueous environment, according to a new study by a team from HZB and Humboldt University in Berlin. Nano-IR spectroscopy with s-SNOM at the IRIS beamline is now suitable for examining tiny biological samples in liquid medium in the nanometre range and generating infrared images of molecular vibrations with nanometre resolution. It is even possible to obtain 3D information. To test the method, the team grew fibroblasts on a highly transparent SiC membrane and examined them in vivo. This method will provide new insights into cell biology.
- Porous Radical Organic framework improves lithium-sulphur batteriesA team led by Prof. Yan Lu, HZB, and Prof. Arne Thomas, Technical University of Berlin, has developed a material that enhances the capacity and stability of lithium-sulphur batteries. The material is based on polymers that form a framework with open pores (known as radical-cationic covalent organic frameworks or COFs). Catalytically accelerated reactions take place in these pores, firmly trapping polysulphides, which would shorten the battery life. Some of the experimental analyses were conducted at the BAMline at BESSY II.