George Srajer
Argonne National Laboratory
After brief introduction to the formalism of magnetic scattering, we will discuss two examples that best illustrate the utility of using x-rays to study intriguing magnetic properties of matter.
The emphasis of the talk will be on the first example that demonstrates how sophisticated x-ray techniques can reveal the atomic origin of magnetic strength (or hardness) in the best permanent magnet known today: Nd2Fe14B. Making stronger and smaller magnets is very important because smaller magnets save energy. This is significant because permanent magnets are ubiquitous in our daily life: from starters in cars to disk drives in computers. In the Nd2Fe14B single crystal there are two neodymium (Nd) ions that are responsible for the magnetic strength. However, our results show that only one of the two Nd ions contributes to the magnetic strength. This opens a possibility for manipulating the local atomic structure around rare-earth ions so one can make even stronger magnets.
In the second example, we show direct imaging by means of x-ray photoemission electron microscopy of the dynamics of magnetic vortices confined in micron-sized circular permalloy (FeNi) dots that are 30 nm thick. The vortex core positions oscillate on a 10 ns time scale after the magnetic field is turned off. The measured oscillation frequencies as a function of the aspect ratio of the dots are in agreement with theoretical calculations presented for the same geometry.
Both examples showcase the application of synchrotron x-rays techniques in the area of magnetism studies and their potential relevance in everyday life.
*Work at Argonne was supported by the U.S. Department of Energy Office of Science, under Contract No. DE-AC02-06CH11357.
Friday, February 20 at 4:00 PM
Room L211, Technological Institute
Refreshments are served at 3:30 PM
