Keywords: accelerator physics (174) BESSY II (269) spintronics (93)

News    27.05.2010

First the orbit, then the spin

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
  • <p>Experiments at the femtoslicing facility of BESSY II revealed the ultrafast angular momentum flow from Gd and Fe spins to the lattice via orbital moment during demagnetization of GdFe alloy.</p>SCIENCE HIGHLIGHT      10.05.2019

    Laser-driven Spin Dynamics in Ferrimagnets: How does the Angular Momentum flow?

    When exposed to intense laser pulses, the magnetization of a material can be manipulated very fast. Fundamentally, magnetization is connected to the angular momentum of the electrons in the material. A team of researchers led by scientists from the Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy (MBI) has now been able to follow the flow of angular momentum during ultrafast optical demagnetization in a ferrimagnetic iron-gadolinium alloy at the femtoslicing facility of BESSY II. Their results are helpful to understand the fundamental processes and their speed limits. The study is published in Physical Review Letters. [...]


  • <p>Tomography of a lithium electrode in its initial condition.</p>SCIENCE HIGHLIGHT      06.05.2019

    3D tomographic imagery reveals how lithium batteries age

    Lithium batteries lose amp-hour capacity over time. Microstructures can form on the electrodes with each new charge cycle, which further reduces battery capacity. Now an HZB team together with battery researchers from Forschungszentrum Jülich, the University of Munster, and partners in China have documented the degradation process of lithium electrodes in detail for the first time. They achieved this with the aid of a 3D tomography process using synchrotron radiation at BESSY II (HZB) as well at the Helmholtz-Zentrum Geesthacht (HZG). Their results have been published open access in the scientific journal "Materials Today". [...]


  • <p>SnSe is a highly layered orthorhombic structure. SnSe undergoes a phase transition of second order at 500&deg;C with an increase of the crystal symmetry from space group Pnma (left) to Cmcm (right).</p>SCIENCE HIGHLIGHT      24.04.2019

    High-efficiency thermoelectric materials: new insights into tin selenide

    Tin selenide might considerably exceed the efficiency of current record holding thermoelectric materials made of bismuth telluride. However, it was thought its efficiency became enormous only at temperatures above 500 degrees Celsius. Now measurements at the BESSY II and PETRA III synchrotron sources show that tin selenide can also be utilised as a thermoelectric material at room temperature – so long as high pressure is applied. [...]




Newsletter