First the orbit, then the spin

Christian Stamm at BESSY II-beamline for femtoslicing

Christian Stamm at BESSY II-beamline for femtoslicing

Novel storage materials of the future will be made out of magnetic films. Researchers at HZB are the first to find out just how fast magnetic particles can be controlled.

Christian Stamm and his colleagues at the Helmholtz-Zentrum Berlin für Materialien und Energie (HZB) can look back on six years of pioneering work at the synchrotron BESSY II. They have set up a unique experiment on so-called femtoslicing, and are now publishing a result obtained in collaboration with an external user group.

Together with their colleagues from Strasbourg, they report in the upcoming issue of Nature (Volume: 465, Pages: 458–461, DOI: 10.1038/nature09070) how fast the magnetism of a material can be influenced. They have observed that an electron’s motion around the atom core – its orbital moment – and its intrinsic angular momentum (spin) respond differently to outside influence.

“The ultra-fast processes contributing towards the phenomenon of magnetism can only be revealed by femtoslicing,” says Christian Stamm explaining the enormous effort it took the several HZB researchers to set up the experiment at the Berlin synchrotron source BESSY II. They fire ultra-short laser pulses at electrons moving at close to the speed of light in the storage ring.

The electrons struck by these pulses subsequently differ from those that do not encounter the laser beam. The X-ray light these electrons emit during their cycle through the storage ring – the special synchrotron light – now also bears the characteristics added by the laser light. Finally, the magnetic sample is studied using these ultra-short X-ray flashes. What is special about BESSY II is that it is the only place in the world where users will find so called circular-polarized X-ray light for slicing experiments.

And this is absolutely essential for studying spin and orbital moment – the phenomena underlying magnetism.
The results Christian Stamm and his colleagues produced with their femtoslicing experiments provide a fundamental insight: “We were able to demonstrate through what path and how fast the added energy gets into the electron spin,” says the physicist. And ultimately how fast magnetism can be controlled from the outside.

For the spintronic and semiconductor technology industries, who wish to build future computers using “spin up” and “spin down” in place of the parameters “1” and “0”, this finding is certainly another crucial milestone, for it shows in detail how the change in spin takes place.

“The orbital motion of the electrons changes very rapidly when energy is added,” explains Christian Stamm. Unlike the spin, which reacts at a delay. That means “if you want to change the electron spin, the orbital path of the electrons must be disrupted first. Only then does the spin flip.”

IH

You might also be interested in

  • HZB receives funding to make innovations usable more quickly
    News
    23.03.2023
    HZB receives funding to make innovations usable more quickly
    The Helmholtz Association has selected three new innovation platforms that will now be funded. HZB is involved in two of them: The Innovation Platform on Accelerator Technologies HI-ACTS is intended to open up modern accelerators for a wide range of applications, while the Innovation Platform Solar TAP is intended to bring new ideas from the laboratories of photovoltaics research more quickly into an application. In total, HZB will receive 4.2 million euros in grants from the Pact for Research and Innovation over the next three years.


  • Perovskite solar cells from the slot die coater - a step towards industrial production
    Science Highlight
    16.03.2023
    Perovskite solar cells from the slot die coater - a step towards industrial production
    Solar cells made from metal halide perovskites achieve high efficiencies and their production from liquid inks requires only a small amount of energy. A team led by Prof. Dr. Eva Unger at Helmholtz-Zentrum Berlin is investigating the production process. At the X-ray source BESSY II, the group has analyzed the optimal composition of precursor inks for the production of high-quality FAPbI3 perovskite thin films by slot-die coating. The solar cells produced with these inks were tested under real life conditions in the field for a year and scaled up to mini-module size.
  • Superstore MXene: New proton hydration structure determined
    Science Highlight
    13.03.2023
    Superstore MXene: New proton hydration structure determined
    MXenes are able to store large amounts of electrical energy like batteries and to charge and discharge rather quickly like a supercapacitor. They combine both talents and thus are a very interesting class of materials for energy storage. The material is structured like a kind of puff pastry, with the MXene layers separated by thin water films. A team at HZB has now investigated how protons migrate in the water films confined between the layers of the material and enable charge transport. Their results have been published in the renowned journal Nature Communications and may accelerate the optimisation of these kinds of energy storage materials.