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Magnetismus Dienstag<br />

MA 13.68 Di 15:00 Bereich A<br />

Hall-Magnetometrie an mikrostrukturiertem Ni2MnIn, Permalloy<br />

und Nb — •René Eiselt, Christian Uhrich, Guido Meier<br />

und Ulrich Merkt — Institut für Angewandte Physik und Zentrum<br />

für Mikrostrukturforschung, Jungiusstraße 11, 20355 Hamburg<br />

Wir haben mikrostrukturierte Elektroden aus Ni2MnIn und<br />

Permalloy hergestellt, die für Experimente zum spinpolarisierten<br />

Transport in Ferromagnet/Halbleiter-Hybridsystemen geeignet sind.<br />

Mit Hilfe der Hall-Magnetometrie werden die Elektroden bezüglich<br />

ihres mikromagnetischen Verhaltens und der von ihnen ausgehenden<br />

Streufelder auf GaAs-Heterostrukturen untersucht. Zudem wird die<br />

Domänenstruktur der Elektroden ortsaufgelöst in Abhängigkeit eines<br />

externen Magnetfeldes mit dem Magnetkraft-Mikroskop analysiert.<br />

Es ist geplant, die Elektroden auf Hall-Barstrukturen elektrisch<br />

anzukontaktieren und Tunneltransport-Experimente durchzuführen.<br />

Desweiteren haben wir auch mikrostrukturierte Ringe und Scheiben aus<br />

Niob auf Hall-Kreuzen präpariert. Über die Verdrängung des externen<br />

Magnetfelds im Sensorbereich können Rückschlüsse auf Flusszustände<br />

in den Ringstrukturen bzw. den Scheiben gezogen werden. Innerhalb<br />

bestimmter Magnetfeldbereiche beobachten wir stabile Vortice-Zustände<br />

[1]. Ferner lassen sich unterschiedlich große Ringstrukturen mit Scheiben<br />

gleicher Radien vergleichen.<br />

[1] A. K. Geim, S. V. Dubonos, J. J. Palacios, I. V. Grigorieva, M. Henini,<br />

and J. J. Schermer, Phys. Rev. Lett. 85, 1528 (2000).<br />

MA 13.69 Di 15:00 Bereich A<br />

Hall-Magnetometrie an nanostrukturierten Permalloyringen —<br />

•Michael Berginski, Haiko Rolff, Christian Heyn, Detlef<br />

Heitmann und Dirk Grundler — Institut für Angewandte Physik<br />

und Mikrostrukturforschung, Universität Hamburg<br />

In hochintegrierten Schaltungen aus magnetoelektronischen Bauelementen<br />

sind ferromagnetische Strukturen mit geringen Streufeldern<br />

und stabilen Magnetisierungszuständen von besonderem Interesse.<br />

Ringförmige Magnetstrukturen wurden in diesem Zusammenhang<br />

bereits früh diskutiert [1]. Wir haben einzelne Permalloy-Nanoringe auf<br />

mikrostrukturierte Hall-Sensoren integriert und im Detail untersucht.<br />

Die Hysteresekurven zeigen ausgeprägte Sprünge als Funktion eines<br />

äußeren Magnetfeldes, das in der Ebene der Ringe angelegt wird. Die<br />

Sprünge spiegeln die charakteristischen Ummagnetisierungsprozesse<br />

der Nanomagnete wider, was durch mikromagnetische Simulationsrechnungen<br />

bestätigt wird. Insbesondere können wir in Abhängigkeit<br />

von der Weite der Nanostruktur zwischen Ringzuständen mit und<br />

ohne magnetischem Vortex unterscheiden. Die Sprungfelder zwischen<br />

den Zuständen variieren systematisch mit der Größe und Weite<br />

der Ringe. Die Arbeiten werden gefördert durch die DFG über das<br />

Graduiertenkolleg ”Nanostrukturierte Festkörper”.<br />

[1] G. Prinz, US patent 5,542,868 and 6,381,170.<br />

MA 13.70 Di 15:00 Bereich A<br />

Influence of point defects on magnetic vortex structures —<br />

•Michael Rahm 1 , Vladimir Umansky 2 , Werner Wegscheider 1 ,<br />

and Dieter Weiss 1 — 1 Institut für Experimentelle und Angewandte<br />

Physik, Universität Regensburg, D-93040 Regensburg, Germany —<br />

2 Braun Center for Submicron Research, Weizmann Institut, Rehovot<br />

76100, Israel<br />

Micro-Hall magnetometry represents a highly advanced experimental<br />

technique to measure hysteresis loops of individual ferromagnetic particles.<br />

Investigating submicron-sized Permalloy disks, it was shown that<br />

a magnetic vortex structure can be pinned at a lithographically defined<br />

point defect [1]. Here, we compare our Hall measurements with micromagnetic<br />

calculations based on LLG [2] in order to draw a detailed picture<br />

of the pinning process. By simulating the point defect simply as a<br />

hole in the disk, excellent agreement between experiment and calculation<br />

can be achieved, while more complex models of the defect result in<br />

larger deviations from the measurement. These investigations are crucial<br />

to understand the behavior of particles containing two or more defects.<br />

First results showing interesting multistable switching behavior in disks<br />

containing up to four defects are presented.<br />

[1] M. Rahm, J. Biberger, V. Umansky, and D. Weiss, Vortex pinning<br />

at individual defects in magnetic nanodisks, J. Appl. Phys. 93 (10), 7429<br />

(2003). [2] M. Scheinfein, see http://llgmicro.home.mindspring.com/<br />

MA 13.71 Di 15:00 Bereich A<br />

Single crystalline epitaxial Mo(110) strip-line for time resolved<br />

observation of magnetization dynamics. — •D.A. Valdaitsev,<br />

J. Prokop, A. Kukunin, H.J. Elmers, and G. Schönhense — Johannes<br />

Gutenberg-Universität Mainz, Institut für Physik, Staudingerweg<br />

7, D-55099 Mainz<br />

Single crystalline Mo(110) strip-lines have been prepared on α-<br />

Al2O3(11¯20). They are dedicated for temporally and spatially resolved<br />

observation of magnetization dynamics of thin epitaxial magnetic films.<br />

On the strip-line substrate, epitaxial Co(0001) film was deposited in UHV<br />

by molecular beam epitaxy and subsequently covered by a Au capping.<br />

The structure of the Mo(110) strip-line and the Co layer were investigated<br />

using low energy electron diffraction. Atomic force microscopy<br />

and scanning tunneling microscopy (STM) were used for the morphology<br />

characterization and the magnetic properties of Co were investigated exsitu<br />

using magneto-optical Kerr magnetometry. The STM measurements<br />

showed monoatomic terraces of widths varied between 10 and 200 nm on<br />

the molybdenum surface. The quality of the obtained strip-line substrate<br />

is similar to single crystal Mo substrates. The epitaxial hcp Co layer<br />

grown on the strip-line reveals a uniaxial in-plane magnetic anisotropy.<br />

The magnetic easy axis lies in [1¯100] direction parallel to Mo[1¯10], while<br />

the hard axis shows along Mo[001] direction. We demonstrate that the<br />

epitaxial Co films grown on the strip-line are appropriate for investigations<br />

with spin-polarized low energy electron microscopy (SP-DREEM).<br />

We show first images of these samples taken with SP-DREEM in diffraction<br />

and real-image modes.<br />

MA 13.72 Di 15:00 Bereich A<br />

Dipolar induced anisotropy and self ordering in patterned<br />

films — •Katharina Theis-Bröhl 1 , Boris Toperverg 2 , Jeff<br />

McCord 3 , Karsten Rott 4 , Hubert Brückl 4 , and Hartmut<br />

Zabel 1 — 1 Department of Experimental and Solid State Physics,<br />

Ruhr-University Bochum, 44780 Bochum, Germany — 2 Petersburg<br />

Nuclear Physics Institute, 188300 Gatchina, St. Petersburg, Russia —<br />

3 Material Research Institute, Helmholtzstr. 20, 01169 Dresden, Germany<br />

— 4 Department of Physics, University Bielefeld, Universitätsstr. 25,<br />

33615 Bielefeld, Germany<br />

A periodic magnetic stripe array has been studied with a combination<br />

of real and reciprocal space methods: Kerr microscopy and polarized<br />

neutron reflectivity. The basic features of our data are well reproduced<br />

by a theoretical model using DBWA and providing a set of parameters<br />

quantifying the magnetization arrangement in the stripe array system.<br />

While the specular neutron reflectivity measures a mean value of the optical<br />

potential averaged over a number of structural elements within the<br />

neutron coherence length, Bragg diffraction filters out magnetic correlation<br />

effects in the system of individual magnetic units within this length<br />

scale. Off-specular diffuse scattering probes correlations of magnetization<br />

fluctuations on a scale smaller than the coherence length. This all<br />

together gives access to a detailed understanding of the magnetization<br />

arrangement which appears to be quite complex and hardly accessible by<br />

other methods. We acknowledge funding by DFG, SFB 491 and BMBF<br />

032AE8BO.<br />

MA 13.73 Di 15:00 Bereich A<br />

Stress induced domains in patterned magnetic thick films —<br />

•Jeffrey McCord — IFW Dresden, Helmholtzstr. 20, 01169 Dresden<br />

The understanding of domain formation in patterned elements is of<br />

great importance for applications in inductive devices. We report on<br />

the formation of non-Landau-like domain structures due to magnetoelastic<br />

effects in patterned electroplated NiFe and CoNiFe-films with different<br />

composition and saturation-magnetostriction varying from 2 to<br />

+20x10 −6 . Novel domain patterns are observed in the 1µm thick structures.<br />

No closure domains form in the negative magnetostriction samples.<br />

For the first time edge curling walls, known from laminated films, are<br />

seen in µm thick single-layer films. Even small changes in composition<br />

drastically alter the domain structures in the tensile stressed films. For<br />

positive magnetostrictive films, an anisotropy-structured domain pattern<br />

is observed. The domain patterns are discussed in terms of stress-induced<br />

local anisotropy variations derived from finite-element analysis and confirmed<br />

by local anisotropy measurements with µm resolution. Changes<br />

with lateral dimensions down to 1µm are shown. The importance of locally<br />

induced stress anisotropy for the modeling of magnetic devices will<br />

be discussed.

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