Group leader

Fecher, Gerhard
Gerhard Fecher
Senior Chief Research Officer
Phone: +49 351 4646-2240
Fax: +49 351 4646-3002

Physics, Electronic structure

Group Members

Nayak, Jayita
Jayita Nayak
Post-doctoral research scientist
Phone: +49 351 4646-2237

Electronic structure

Sun, Aili
Aili Sun
Post-doctoral research scientist
Phone: +49 351 4646-2255

Electronic structure

Kroder, Johannes
Johannes Kroder
Graduate student
Phone: +49 351 4646-2236

Electronic structure

Former Group Members

Karel, Julie
Julie Karel
Post-doctoral research scientist

Publication highlights

R. Shan, S. Ouardi, G. H. Fecher, L. Gao, A. Kellock, A. Gloskovskii, C. E. Viol Barbosa, E. Ikenaga, C. Felser, and S. S. P. Parkin, "A p-type Heusler compound: Growth, structure, and properties of epitaxial thin NiYBi films on MgO(100)," Applied Physics Letters 101 (21), 212102-1-212102-4 (2012).
Christian G. F. Blum, Siham Ouardi, Gerhard H. Fecher, Benjamin Balke, Xeniya Kozina, Gregory Stryganyuk, Shigenori Ueda, Keisuke Kobayashi, Claudia Felser, Sabine Wurmehl, and Bernd Büchner, "Exploring the details of the martensite-austenite phase transition of the shape memory Heusler compound Mn2NiGa by hard x-ray photoelectron spectroscopy, magnetic and transport measurements," Applied Physics Letters 98 (25), 1-3 (2011).
Siham Ouardi, Gerhard H. Fecher, Benjamin Balke, Xenia Kozina, Gregory Stryganyuk, Claudia Felser, Stephan Lowitzer, Diemo Ködderitzsch, Hubert Ebert, and Eiji Ikenaga, "Electronic transport properties of electron- and hole-doped semiconducting C1b Heusler compounds: NiTi1-xMxSn (M=Sc, V)," Physical Review B 82 (8), 1-9 (2010).


Hard X-ray photoelectron spectroscopy (HAXPES) is a well-adaptable non-destructive technique for the analysis of electronic bulk states, buried films and interfaces. This technique provides important information for the design of new Heusler compounds.

HAXPES is a photoemission technique that employs hard X-ray (photon energy > 3000 eV). The excitation by hard X-ray results in the emission of electrons with high kinetic energies and, consequently, in very large probing depth. The probe of real bulk states allows a more reliable comparison between experimental spectra and theoretical predictions in Heusler compounds.

  • Chemical Analysis
  • Electronic Structure
  • Depth Profile
  • Crystal Ordering
  • Magnetic Ordering

HAXPES is a versatile technique

HAXPES is able to determine the symmetry of the states composing the valence band. Circularly polarized hard X-rays allows the investigation of magnetic properties  in  multilayer structures.  Even structural properties can be investigated by using the angular distribution of the high kinetic energy photoelectrons.

Our group has extensively investigated the electronic properties of Heusler compounds for spintronics, magneto shape memories and thermoelectric applications. We have studied the changes in the electronic structure upon chemical substitution or induced phase transitions. Many properties of Heusler compounds are essentially connected to the valence band, which is formed by bonding and hybridized states. The measurement of valence band states by HAXPES is used as validation and feedback for the calculation and tailoring of the Heusler properties. Using HAXPES, we are able to investigate the interfaces of multilayer structures, which is important for devices applications (e.g. magneto tunneling junctions). More recently we have investigated also new materials  as topological insulator and new phases induced by ionic liquid electrolyte.

<div style="text-align: justify;"><strong>Figure 1:</strong> <em>Investigation of  the Electronic Structure of Heusler Compounds.</em></div> Zoom Image
Figure 1: Investigation of  the Electronic Structure of Heusler Compounds.


X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) are powerful techniques to probe the electronic and magnetic structure of materials and are used extensively in our group to investigate Heusler compounds, strongly correlated electron systems and other oxide materials.

Heusler compounds are promising for many magnetism-related applications such as spintronics, magnetocalorics and hard magnets.  In particular, the Mn-containing thin film compounds are especially compelling, where the presence of Mn on two inequivalent sublattices leads to a wide variety of interesting properties (e.g. non-collinear magnetism, large exchange bias) and potential device applications (e.g. STT-RAM).  Bulk Heusler alloys are also being investigated for magnetocalorics and rare-earth free hard magnets.  The element specificity of L-edge XAS and XMCD grants the opportunity to probe the magnetic properties of these materials, including the individual magnetic sublattices.

We have also begun to investigate strongly correlated electron systems and other oxide materials, where the orbital polarization in novel states of matter induced by liquid electrolyte gating can be probed. Finally, we have recently used K-edge XAS to probe the valance states in a series of Mn-containing bulk Heusler compounds.

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