Thomas Feggeler

Brookhaven National Laboratory

National Synchrotron Light Source II
Bldg. 741, Room 1L150
P.O. Box 5000
Upton, NY 11973-5000

(631) 344-8175
(341) 799-6413
tfeggeler1@bnl.gov

Expertise | Research | Education | Appointments | Publications | Awards

Expertise

• X-Ray Spectromicroscopy
• (Time-Resolved) Scanning Transmission X-Ray Microscopy ((TR-)STXM)
• X-Ray Magnetic Circular and Linear Dichroism (XMCD/XMLD)
• Ferromagnetic Resonance Spectroscopy
• Electron Paramagnetic Resonance Spectroscopy
• Magnetometry
• Micromagnetics
• Magnetic Materials
• Magnetic Interactions
• Spintronics/Magnonics
• Photolithography

Research Activities

Coulomb phase physics in artificial spin ice | Physique des phases de Coulomb dans une glace de spin artificielle

This project funded by the Agence Nationale de la Recherche (ANR) and the German Research Foundation (DFG-545505173) aims at studying the physics of Coulomb phases in artificial spin ice matter. In particular, we plan to carry out a set of experiments allowing us to probe, in real space and time, the properties of Coulomb phase excitations, which behave as magnetically charged quasiparticles. These quasiparticles, often referred to as magnetic monopoles, are theoretically described by the laws of electrostatics: they repel or attract depending on the (magnetic) charge they carry and interact via a Coulomb potential at long distances. However, these properties (among others that we will also study) have never been visualized, directly and unambiguously, in an experimental system. This is what we intend to achieve in this project. In other words, we propose here to test experimentally, by employing transmission electron microscopy and x-ray microscopy, in two-dimensional frustrated arrays of interacting nanomagnets subjected to thermal fluctuations, the relevance of several theoretical predictions developed these last fifteen years and largely employed in frustrated magnetism.

In collaboration with:
Université Grenoble Alpes | Institut Néel CNRS, Grenoble (France) - Nicolas Rougemaille
University of Duisburg-Essen | Faculty of Physics, Duisburg (Germany)  - Katharina Ollefs
Forschungszentrum Jülich | Ernst Ruska-Centrum (ER-C), Jülich (Germany) - Rafal Dunin-Borkowski
University of California, Berkeley | Department of Physics, Berkeley CA (US) - Roger Falcone
Lawrence Berkeley National Laboratory | Advanced Light Source, Berkeley CA (US) - Hendrik Ohldag

X-ray absorption spectroscopy under external stimuli – microscopic understanding and tailoring hysteresis

Collaborator in the sub-project A03 within the Collaborative Research Center TRR270 - German Research Foundation Project 405553726. In the project a combination of Mössbauer/X-ray spectroscopy and X-ray microscopy will be employed to derive a microscopic element-specific understanding of hysteresis in permanent magnet materials to disentangle their intrinsic and extrinsic properties.

In collaboration with:
University of Duisburg-Essen | Faculty of Physics, Duisburg (Germany) - Katharina Ollefs (project lead)
Technical University of Darmstadt | Functional Materials, Darmstadt (Germany) - Oliver Gutfleisch
Université Grenoble Alpes | Institut Néel CNRS, Grenoble (France) - Nora Dempsey
Lawrence Berkeley National Laboratory | Advanced Light Source, Berkeley CA (US) - Hendrik Ohldag
 

Education

Ph.D. (Dr. rer. nat.), University of Duisburg Essen, Duisburg (Germany) November 20^th 2020, Ph.D. Thesis: “Element-specific detection of magnetization dynamics using Scanning Transmission X-ray Microscopy“. 

M.Sc., Physics, University of Duisburg-Essen, Duisburg (Germany) May 20^th 2016, M.Sc.-Thesis: “Mikromagnetische Simulationen zur statischen und dynamischen Charakterisierung von Nanopartikeln“ (Micromagnetic simulations for the static and dynamic characterization of nano particles).

B.Sc., Physics, University Duisburg-Essen, Duisburg (Germany) September 26^th 2011, B.Sc.-Thesis: "Bau eines Spektrometers zur Messung der Ferromagnetischen Resonanz mittels magnetooptischem Kerr-Effekt“ (Construction of a spectrometer for the measurement of ferromagnetic resonance by means of the magneto-optical Kerr effect).

Professional Appointments

Roles:

Research Staff Scientist - August 2024 – Today - in the Imaging & Microscopy Program at the National Synchrotron Light Source II at Brookhaven National Laboratory. 

Postdoctoral Researcher - March 2023 – August 2024 - in the research group of Roger W. Falcone at the University of California, Berkeley | Department of Physics | STROBE NSF Science and Technology Center on Real-Time Functional Imaging.

Postdoctoral Researcher - February 2021 – February 2023 - in the Microscopy Group at the Advanced Light Source at Lawrence Berkeley National Laboratory.

Postdoctoral Researcher - December 2020 – January 2021 - in the research group of Heiko Wende at the University of Duisburg-Essen.

Committees:

AVS Science and Technology of Materials, Interfaces, and Processing: Executive Committee Member of the Magnetic Interfaces & Nanostructures Division (2025 to present).

Selected Publications

• Kräenbring M, Bomm K, Bendt G, et al (2025) Bottom-Up Synthesis of Metallic CoNi Nanoplatelets with Magnetic Vortex-Like Spin Configurations. Small Science. https://doi.org/10.1002/smsc.202500111
• Efremova MV, Wiedwald U, Sigmund F, et al (2025) Genetically Controlled Iron Oxide Biomineralization in Encapsulin Nanocompartments for Magnetic Manipulation of a Mammalian Cell Line. Advanced Functional Materials. https://doi.org/10.1002/adfm.202418013
• Feggeler T, Meckenstock R, Strusch T, et al (2024) An Ultrasensitive Molecular Detector for Direct Sensing of Spin Currents at Room Temperature. ACS Applied Materials & Interfaces 16:54139–54145. https://doi.org/10.1021/acsami.4c09015
• Zingsem BW, Feggeler T, Spoddig D, et al (2024) Reciprocity relations in a biologically inspired nanomagnonic system with dipolar coupling. Applied Physics Letters 124:. https://doi.org/10.1063/5.0195215
• Feggeler T, Levitan A, Marcus MA, et al (2023) Scanning transmission X-ray microscopy at the Advanced Light Source. Journal of Electron Spectroscopy and Related Phenomena 267:147381. https://doi.org/10.1016/j.elspec.2023.147381
• Feggeler T, Lill J, Günzing D, et al (2023) Spatially-resolved dynamic sampling of different phasic magnetic resonances of nanoparticle ensembles in a magnetotactic bacterium Magnetospirillum magnetotacticum. New Journal of Physics 25:043010. https://doi.org/10.1088/1367-2630/acc81f
• Zingsem B, Feggeler T, Meckenstock R, et al (2023) Evaluation protocol for revealing magnonic contrast in TR-STXM measurements. AIP Advances 13:. https://doi.org/10.1063/5.0145753
• Feggeler T, Meckenstock R, Spoddig D, et al (2022) Element-specific visualization of dynamic magnetic coupling in a Co/Py bilayer microstructure. Scientific Reports 12:. https://doi.org/10.1038/s41598-022-23273-y
• Feggeler T, Meckenstock R, Spoddig D, et al (2021) Spatially resolved GHz magnetization dynamics of a magnetite nano-particle chain inside a magnetotactic bacterium. Physical Review Research 3:. https://doi.org/10.1103/physrevresearch.3.033036
• Josten N, Feggeler T, Meckenstock R, et al (2020) Dynamic unidirectional anisotropy in cubic FeGe with antisymmetric spin-spin-coupling. Scientific Reports 10:. https://doi.org/10.1038/s41598-020-59208-8
• Pile S, Feggeler T, Schaffers T, et al (2020) Non-standing spin-waves in confined micrometer-sized ferromagnetic structures under uniform excitation. Applied Physics Letters 116:. https://doi.org/10.1063/1.5139881
• Zingsem BW, Feggeler T, Terwey A, et al (2019) Biologically encoded magnonics. Nature Communications 10:. https://doi.org/10.1038/s41467-019-12219-0
• Schaffers T, Feggeler T, Pile S, et al (2019) Extracting the Dynamic Magnetic Contrast in Time-Resolved X-Ray Transmission Microscopy. Nanomaterials 9:940. https://doi.org/10.3390/nano9070940
• Scheibel F, Zingsem B, Feggeler T, et al (2019) Magnetic anisotropy of single-crystal antiperovskite Mn3GaC studied by ferromagnetic resonance and dynamic magnetic-response simulations. Physical Review Materials 3:. https://doi.org/10.1103/physrevmaterials.3.054403
• Schaffers T, Meckenstock R, Spoddig D, et al (2017) The combination of micro-resonators with spatially resolved ferromagnetic resonance. Review of Scientific Instruments 88:. https://doi.org/10.1063/1.4996780

Awards & Recognition

Center for Nanointegration Duisburg-Essen (CENIDE) Best Paper Award 2024 in Magnetism for New Journal of Physics 25, 043010 (2023) "Spatially-resolved dynamic sampling of different phasic magnetic resonances of nanoparticle ensembles in a magnetotactic bacterium Magnetospirillum magnetotacticum"

AVS Magnetic Interfaces and Nanostructures Division Postdoctoral Award 2023.

Center for Nanointegration Duisburg-Essen (CENIDE) Best Paper Award 2021 in Magnetism for PHYSICAL REVIEW RESEARCH 3, 033036 (2021) „Spatially resolved GHz magnetization dynamics of a magnetite nanoparticle chain inside a magnetotactic bacterium“.