Plenarvorträge - DPG-Tagungen

Magnetismus Montag
MA 8.7 Mo 17:15 H22
Magnetic and elastic properties of YCo5 under pressure —
•Daniela Koudela 1 , Ingo Opahle 1 , Manuel Richter 1 , Klaus
Koepernik 1 , Ulrike Nitzsche 1 , Helge Rosner 2 , Michael
Kuzmin 3 , and Helmut Eschrig 1 — 1 IFW Dresden, PF 270116, 01171
Dresden — 2 MPI-cPfS Dresden, Nöthnitzer Straße 40, 01187 Dresden
— 3 Instituto de Ciencia de Materiales de Aragon, Zaragoza; Spain
We computed the total energy and the magnetic moment of YCo5
in dependence of the lattice parameters. Our calculations are based on
density functional theory in the local spin density approximation. In accordance
with earlier calculations of Yamada et al. [J. Phys.: Condens.
Matter 11 (1999) 483] we find a transition from high spin to low spin under
applied pressure. On the other hand our calculations show a strong
dependence of the magnetic moment on volume in the low spin state close
to the transition volume not observed by the previous authors. This is
connected with a change in the bulk modulus from about 200 GPa to 60
GPa at the transition, which takes place at a pressure of about 9 GPa.
The calculations were done with the full-potential local-orbital method
(FPLO).
MA 8.8 Mo 17:30 H22
Magnetismus und elektronische Struktur von Gadolinium
— •C. Santos 1 , V. Eyert 2 und W. Nolting 1 — 1 Lehrstuhl
Festkörpertheorie, Institut für Physik, Humboldt-Universität zu Berlin
— 2 Institut für Physik, Theoretische Physik II, Universität Augsburg
Durch Kombination einer vielteilchentheoretischen Auswertung des
Kondo-Gitter-Modells mit einer ,,ab initio“ Bandstrukturrechnung bestimmen
wir sowohl die temperaturabhängige elektronische Struktur als
MA 9 Hauptvortrag Demokritov
auch die magnetischen Eigenschaften von HCP-Gadolinium. Das Vielteilchenproblem
wird mit der in Phys. Rev. B 65 144419 vorgestellten Green-
Funktion-Theorie behandelt. Diese haben wir auf das Mehrband-Kondo-
Gitter Modell erweitert und anschließend mit einer ASW-Bandstruktur
kombiniert, wobei Doppelzählung von relevanten Wechselwirkungen vermieden
werden konnte. In diesem Beitrag werden Ergebnisse der selbstkonsistent
berechneten Curie-Temperatur TC, der Magnetisierung 〈S z 〉
und der temperaturabhängigen Quasiteilchen-Bandstruktur vorgestellt.
Es ergibt sich eine fast quantitative Übereinstimmung mit experimentellen
Daten.
MA 8.9 Mo 17:45 H22
Structure and Magnetism of Light Actinides and Their Compounds:
Theorie — •Manuel Richter, Ingo Opahle, Ulrike
Nitzsche, Klaus Koepernik, and Helmut Eschrig — IFW Dresden,
PF 270116, D-01171 Dresden
Structural and magnetic properties of actinides and actinide compounds
are much influenced by spin-orbit interaction and other relativistic
effects. By means of the recently developed fully relativistic fullpotential
local-orbital (R-FPLO, [1]) scheme, we have evaluated equilibrium
volume, bulk modulus, and structural energies of light actinide
metals in the framwork of the local density approximation. In particular,
we find evidence for the existence of a hexagonal Uranium phase
in thin films on W(110) and for the possible existence of cubic Protactinium.
Using the local spin density approximation with orbital polarization
corrections, the magnetic properties of cubic Uranium Sulfide are
investigated.
[1] http://www.ifw-dresden.de/FPLO/
Zeit: Dienstag 09:30–10:00 Raum: H10
Hauptvortrag MA 9.1 Di 09:30 H10
Experimental observation of symmetry breaking soliton modes
in an active ring — •Sergej O. Demokritov 1 , Alexander
A. Serga 1 , Vladislav E. Demidov 1 , Burkard Hillebrands 1 ,
Michail P. Kostylev 2 und Boris A. Kalinikos 2 — 1 Fachbereich
Physik, Technische Universitaett Kaiserslautern, Erwin-Schroedinger-
Strasse 56, 67663 Kaiserslautern, Germany — 2 St. Petersburg Electrotechnical
University, 197376 St. Petersburg, Russia
Solitons are large-amplitude, spatially confined wave packets in nonlinear
media. A unique feature is their propagation without a change in
shape owing to the stabilizing effect of the nonlinearity. We report on the
first experimental study of solitons in an active ring and their novel pro-
MA 10 Exchange Bias
perties due to phase quantization [1]. As a model system, we constructed
an active nonlinear ring based on spin-wave propagation in a magnetic
film. To address individually each eigen-mode of the ring a newly developed
mode selecting mechanism based on phase sensitive amplification
has been used. Several novel symmetry-breaking soliton-like modes are
found, such as Möbius solitons, which break the fundamental symmetry
of 2p-periodicity in the phase change acquired per loop: a Möbius soliton
needs to travel twice around the ring to meet the initial phase condition.
A phase sensitive interaction between soliton-like modes has been discovered.
This interaction provides the phase correlation between two travelling
solitons if their distance is decreasing. [1] S.O. Demokritov et al.
Nature 426, 159 (2003).
Zeit: Dienstag 10:15–13:00 Raum: H10
MA 10.1 Di 10:15 H10
Exchange coupling in thin Fe-films on NiO(001) — •U. Mick,
W. G. Park, V. Bocatius, H. Meinert, and E. Kisker — Institut
für Angewandte Physik, Universität Düsseldorf
The domain formation and exchange coupling of thin Fe-Films on
NiO(001) have been investigated by x-ray magnetic linear dichroism
(XMLD) and x-ray magnetic circular dichroism (XMCD) in photoemission
electron microscopy (PEEM).
In-situ cleaved NiO crystals provide atomically defined clean NiO(001)surfaces
as is shown in complementary STM-measurements. Thin Fe-films
grown by MBE at room temperature on these NiO(001)-surfaces exhibit
a collinear coupling of their magnetic moments to the spin structure of
by the NiO(001)-substrate as is revealed in angular dependent PEEMmeasurements.
Fe-films grown on freshly cleaved NiO(001) can induce
changes in the NiOs AF-domains, which are presumably thermodynamically
unstable. Thermally relaxed NiO(001) surfaces, that have been annealed
above Neel-temperature, show a rearrangement in their domain
structure that is not altered by subsequent deposition of Fe anymore while
the Fe-films still show collinear coupling after the onset of FM-coupling,
as has been investigated for different film thicknesses of Fe from 1 ML to
15 ML.
Neither x-ray absorption spectroscopy (XAS) nor PEEM-investigations
on Ni-MCD gave any evidence for significant interface reactions between
the Fe-films grown at room temperature and the NiO substrate.
This work has been performed at BESSY-UE52 and was supported by
the BMBF under grant No. 05KS1PFB/1
MA 10.2 Di 10:30 H10
Soft X-ray Resonant Magnetic Scattering studies on CoO/Fe
exchange bias bilayers — •Florin Radu, Gregor Nowak, Johannes
Grabis, Alexei Nefedov, and Hartmut Zabel — Experimentalphysik/Festkoerperphysik,
Ruhr-Universitaet Bochum, 44780
Bochum, Germany
We have used the ALICE diffractometer and soft X-ray Resonant Magnetic
Scattering (XRMS) techniques to search for the presence of an effective
ferromagnetic moment in an antiferromagnetic (AF) layer which
is in close contact with a ferromagnetic (F) layer. Using rf-sputtering we
have prepared two samples in a single run: one is a CoO(25 ˚A)/Fe(150
˚A) exchange bias system and the other is a single CoO(25 ˚A) AF layer
deposited on a sapphire substrate. The samples were cooled in a field of
+2000 Oe from above the TN=291 K of the CoO AF layer to T=30 K.
Taking advantage of the element specificity of the XRMS technique, we
have measured hysteresis loops of both Fe and CoO layers. The result is
that a single layer of CoO deposited on a substrate shows no ferromagnetic
signal while for the CoO layer deposited on the Fe ferromagnetic
layer we observe hysteresis loops. From these measurements we conclude