X-ray Microscopy of Magnetic Nanostructures

Abstract:

Magnetic nanostructures play a crucial role on modern data storage and processing technology.

Using soft x-ray microscopy and spectroscopy at a National User Facility like e.g. the Advanced Light Source we are able to gain insight into the relevant processes in magnetic nanostructures and complex magnetic interfaces with picosecond time resolution and nanometer spatial resolution.

X-ray based spectroscopy and microscopy have been shown to be a powerful tool for the characterization of complex materials on the nanoscale, from battery materials to topological magnetic monopoles. Using polarization-dependent effects (dichroism), we are able to learn about magnetic, structural, and electronic order, with tens of nanometer spatial resolution. In addition, so-called photon-in, photon-out techniques are insensitive to the presence of external stimuli or even changes in ambient conditions, which allows us to study devices in-operando in state-of-the-art X-ray microscopes. Altogether, these features have led to the development of a strong international user community focused on, e.g., battery devices or magnetic and electric devices. However, the feature that synchrotrons are pulsed sources of X-rays is typically less used by experimentalists.

Synchrotrons operate at repetition rates up to 500 MHz, producing X-ray pulses that are less than 100 picoseconds long with very little temporal jitter (≈10 ps). By using point detectors, e.g., Avalanche Photodiodes, and fast electronics with bandwidths of 10 GHz or more, it is then possible to follow reversible processes with about 10 picoseconds time resolution.

In this talk, I will describe several examples of how we can use synchrotron radiation to gain insight into materials that are otherwise very difficult or impossible to obtain using lab-based methods. I will also describe current efforts to increase sample throughput at synchrotrons, which are typically more geared towards fundamental science than applied technological questions.

Read more: 
     Mutual modulation between surface chemistry and bulk microstructure in nickel-rich layered oxide battery cathode materials
     Imaging Topological Magnetic Monopoles in 3D

Speaker:

Dr. Hendrik Ohldag

Staff Scientist
Spectromicroscopy, Photon Science Operations

The Advanced Light Source
Lawrence Berkeley National Laboratory

IEEE Magnetics Society, IEEE Fellow

Hendrik Ohldag received the Ph.D. in experimental physics from the Universität Düsseldorf, Germany, in 2002.

He joined the Stanford Synchrotron Radiation Light Source (SSRL) in 1999 as a research assistant as part of his Ph.D. research. After a postdoctoral fellowship at SSRL, he became a permanent member of the research staff in 2005 before he joined the Advanced Light Source (ALS) in Berkeley as a staff member in 2018.

Dr. Ohldag’s research focuses on using polarized X-rays generated by a synchrotron to study magnetic materials and complex chemical surfaces and interfaces in advanced X-ray microscope

Dr. Ohldag was awarded the David. A Shirley Award at the ALS in 2006 for “outstanding contribution in using photoemission electron microscopy for the study of magnetic materials."  

Dr. Ohldag is a member of the IEEE Magnetics Society and the chair of the Magnetic Interfaces and Nanoscale Device Division of the American Vacuum Society. He was a Distinguished Lecturer of the IEEE Magnetics Society in 2017.

He has authored or co-authored over 50 peer-reviewed papers and book chapters which have been cited over 2500 times. He has participated in the organization of 25 international conferences and workshops.  He has been named a fellow of the American Physical Society, the American Vacuum Society, and the IEEE. He holds adjunct faculty positions at the University of California, Santa Cruz and Stanford University.”

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