Research Group Dormann
Prof. Dr. Elmar Dormann
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Diplom: 1966 TH Darmstadt
1966-1967 Ecole Normale Supérieure, Paris
Ph.D.: 1969 TH Darmstadt
1973-1974 UCSB, USA
Habilitation: 1975, TH Darmstadt
1977-1991 Professur Universität Bayreuth
1985 UCSB, USA
seit 1991 Professur Universität Karlsruhe
Fields of Research: Experimental solid-state physics, Chemical Physics, Magnetism (magnetometry, ESR, NMR, double resonance techniques, ESR imaging, microwave conductivity), Organic Conductors with Peierl's transition, molecular magnetism , hyperfine interaction in metals and intermetallic compounds (4f/3d-compounds, ferromagnets, heavy-fermion compounds, hydrids).
NMR spectrometer Bruker MSL 300 for nuclear magnetic double resonance (300 MHz und 5-125 MHz) under magic angle spinning (7T superconducting magnet).
In this group, static and resonant magnetic methods are used to characterize crystalline solids with interesting physical properties:
SQUID-magnetometry and microwave conductivity give integral information. Local information is obtained by electron spin resonance in microwave and radiofrequency range, solid-state fourier transform pulsed nuclear resonance (3.5 - 450 MHz) and various double resonance techniques. Via combination of these local and integral measure methods, particularly detailed information of the electronic properties is derived.
Metal - non metal transition
13C-solid-state-spectra PE-MAS-spectrum of (PE)2PF6*2/3THF
Within the frames of the Sonderforschungsbereich 195 the metal - non metal transiton of crystalline solids is studied with magnetic methods.
Many organic and some inorganic, electrically conductive crystals show pronounced anisotropy of their electrical conductivity.
Quasi-one dimensional metals are realized by appropriate structural arrangement of the building units. Single crystals of the radical cation salts of arenes like Naphtalene, Fluoranthene, Pyrene and Perylene with inorganic complex anions like PF6 can be grown electrochemically from appropriate solvents. Their charge carriers have weak electron-electron and spin-orbit interaction, but strong electron-phonon interaction. Thus most of these quasi-one dimensional organic conductors show a Peierls-like metal-non metal transition below room temperature that is studied as function of stoichiometry and defect concentration.
With the magnetic resonance methods we derive electronic wave functions, electron and nuclear spin dynamics, influence of molecular motions, and spatial restrictions to electron spin motion.
Magnetic resonance techniques are also applied for the doped semiconductor Si:P or for Lanthanium hydrides (LaHx, with x between 2 and 3) in the concentration range of the respective metal-insulator transition.
One of the home-built NMR probeheads
The electronic properties, and indirectly also the structural properties, of pyrolytic carbon are analyzed within the cooperative efforts of the Sonderforschungsbereich 551, focussed on "Carbon from the gas phase: elementary reactions, structures, materials". Chemical vapor deposition and infiltration are characterized by electron-spin resonance and electron-spin proton double-resonance.
In the last decade the magnetic properties of organic solids received renewed interest - their mechanical and electrical properties being applied already much longer. In cooperation with chemists our group is engaged in screening type investigations in an attempt for tailoring of magnetic properties of organic materials.
In addition to magnetic techniques also caloric methods are used. Wave functions and interactons of molecular electron spins are characterized experimentally and by model calculations.
Rare-earth inter metallic compounds
73Ge zero-field NMR spectra of GdxY1-xMn6Ge6 at T = 4.2 K
The combination of SQUID-magnetometry and nuclear magnetic resonance is used for the analysis of the magnetic interactions in inorganic, especially intermetallic compunds with 3d- and 4f-transition elements.
The stability of manganese moments is studied in rare earth-manganese ternary compounds (e.g. RMn2-hydrides as RMn6Ge6 compounds).
The conduction electron polarization in heavy fermion compounds (e.g. CeCu6-xAux) is monitored by 63/65Cu-NMR.
For the correlation of microscopic interactions and macroscopic magnetic properties the nuclei are especially appropriate as local probes, because magnetic and frequently also electric hyperfine interaction, occasionally even for different structured sites, can be exploited.