Group leader

Fecher, Gerhard
Gerhard Fecher
Senior Chief Research Officer

Phone: +49 351 4646-2240
Fax: +49 351 4646-3002
Room: B1.2.40

Physics, Electronic structure

Group Members

He, Yangkun
Yangkun He
Post-doctoral research scientist

Phone: +49 351 4646-3424
Room: B3.3.24

Magnetic and topological Heusler compounds

Ranjbar, Reza
Reza Ranjbar
Post-doctoral research scientist

Room: extern

Heusler Thin films

Yao, Mengyu
Mengyu Yao
Post-doctoral research scientist

Phone: +49 351 4646-2238
Room: B1.2.38

Photo emissions


Kroder, Johannes
Johannes Kroder
Graduate student

Phone: +49 351 4646-3205
Room: B1.3.05

Synthesis and magnetic heusler compounds

Ole Petzold
Research technician

Phone: +49 351 4646-2230
Fax: +49 351 4646-3002
Room: B1.2.38

Undergraduate Students

Bannies, Jörn
Jörn Bannies
Research student

Phone: +49 351 4646-2273
Room: B1.3.01

Synthesis and photoelectron spectroscopy

Kautzsch, Linus
Linus Kautzsch
Research student

Phone: +49 351 4646-3205
Room: B1.3.05

Synthesis and superconductors

Mende, Felix
Felix Mende
Undergraduate student

Phone: +49 351 4646-3205
Room: B1.3.05

Synthesis and Heusler compounds

Former Group Members

Stinshoff, Rolf
Rolf Stinshoff
Graduate student

Room: extern

Synthesis

Haxpes

Header image 1435229847

Electronic Structure - G. H. Fecher

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.

Figure 1: Investigation of  the Electronic Structure of Heusler Compounds. Zoom Image
Figure 1: Investigation of  the Electronic Structure of Heusler Compounds.

XAS & XMCD

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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