S. Dreyer

University of Göttingen

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S. Sievers

Physikalisch-Technische Bundesanstalt

Ch. Jooss

University of Göttingen

Jonas Norpoth

Clausthal University of Technology

U. Siegner

Physikalisch-Technische Bundesanstalt

Ch. Lang

Universitätsmedizin Göttingen

C. Herweg

University of Göttingen

H.C. Freyhardt

University of Göttingen

P. Troche

University of Göttingen

José Ayala

University of Tarapacá

Christian Jooß

University of Göttingen

Cooperative Institutions

University of Göttingen

Max Planck Society

Universitätsmedizin Göttingen

Clausthal University of Technology

Physikalisch-Technische Bundesanstalt

Institut de Ciència de Materials de Barcelona

Technische Universität Braunschweig

ETH Zurich

Brookhaven National Laboratory

Max Planck Institute for Biophysical Chemistry

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Entwicklung eines quantitativen Verfahrens zur Streufeld- und Magnetisierungsbestimmung magnetischer Strukturen

S. Dreyer

This work deals with the full quantitative local reconstruction of magnetization distributions from measurements of the normal component of the magnetic stray field of micro- and nanostructured magnetic films and the underlying inverse magnetostatic problem. The magneto-optical indicatorfilm technique (MOIF) is applied for magnetic imaging. Based upon the strong magneto-optical Faraday-effect in special sensor layers, this method allows a quantitative determination of the stray field z-component at a fixed height above the samples. Lithographically patterned, magnetically hard structures of well defined shape and size serve as model systems for the investigation and establishment of the relationship between the stray field and the underlying magnetization. The quantitative stray field measurements via MOIF are verified by theoretical simulations. The evaluation of the local magnetization distribution is based on transfer functions in Fourier space, taking all intrinsic measuring conditions into account. This formalism leads to a correct quantitative reconstruction of the magnetization for pattern sizes larger than the resolution limit. Constitutive upon the advanced mathematical inversion scheme, the early stages of the remagnetization process of spatially extended arrays of magnetically hard elements are studied in detail. Furthermore, this work treats the problem of calibrating a magnetic force microscope by means of quantitative MOIF measurements.

Faraday cage

10.53846/goediss-2650

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Nanostructuring of Multilayers by a Thermally Driven Self Assembling Process

MRS Proceedings (2001)

C. Herweg S. Dreyer P. Troche José Ayala S. Sievers

Non-blocking I/O

Component (thermodynamics)

10.1557/proc-704-w6.35.1

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Nanostructuring of Multilayers by a Thermally Driven Self Assembling Process

MRS Proceedings (2001)

C. Herweg S. Dreyer P. Troche José Ayala S. Sievers

Non-blocking I/O

Component (thermodynamics)

10.1557/proc-707-w6.35.1

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Citations (1)

Quantitative imaging of stray fields and magnetization distributions in hard magnetic element arrays

Journal of Applied Physics (2007)

S. Dreyer Jonas Norpoth Christian Jooß S. Sievers U. Siegner

In order to determine magnetic stray field and magnetization distributions of thin magnetic patterns and arrays, we developed a new quantitative imaging technique based on magneto-optical indicator films (MOIF) combined with inverse magnetostatic methods. The method is applied to hard magnetic FePt and PrCo5 films which exhibit out-of-plane and in-plane easy magnetization axes, respectively. The films are patterned with standard electron beam lithography into square shaped elements with sizes between 10 μm and 500 nm. The magnetization values obtained from the MOIF method are compared to those of integral magnetometer measurements and show a good agreement, if the sensor properties are taken into account, properly. As an outlook, a concept for combining MOIF imaging with magnetic force microscopy is demonstrated which allows for quantitative magnetization imaging with a resolution down to 10 nm.

10.1063/1.2717560

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Citations (21)

Online Help; The implementation of user manuals into a radar application from Saab Microwave Systems

S. Dreyer

This thesis was done at Saab Microwave Systems, a business unit at Saab AB, and focused on how Online Help (OH) could be implemented in one of their products, as well as if it was possible to use the already existing documentation to create the help content to the OH without having to rewrite it all. Suitable OH platforms were researched and tested. Afterwards it was decided to use JavaHelp because it was the most versatile as well as supported Pop-ups. The development process was done iteratively with three prototypes. Between each phase a usability test was carried out, and the result was used in the creation of the following prototype. The third prototype included a fully implemented OH system with online manual, F1 key support to access it and Pop-up help in the whole application. The third test let the testers complete an assignment by either using the traditional manuals or the OH, in order to see if there was an advantage to use one over another. The conclusion is that it is possible to, cheaply and relatively easy, implement OH in an already finished application. Although JavaHelp is far from a perfect solution and need more work if it is going to be used commercially. It is also possible to create online manuals from already existing documentation such as Framemaker or Word documents by using RoboHelp. ------------------------------------------------------------ Sammanfattning: Det har examensarbetet gjordes pa Saab Microwave Systems, en affarsenhet inom Saab AB, och handlade om hur Online Hjalp (OH) kunde bli implementerad i en av deras produkter, men aven att ta reda pa om redan existerande dokumentation kunde anvandas for att skapa hjalp materialet till OH utan att behova skriva om allt. Lampliga OH plattformar undersoktes och testades, i slutandan bestamdes det att JavaHelp skulle anvandas pga dess mangsidighet och att det stodde Pop-ups. Utvecklingsprocessen gjordes iterativt med tre prototyper. Mellan varje fas sa gjordes ett anvandningstest vars resultat sedan anvandes i utvecklingen av nasta prototyp. Den tredje prototypen innefattade en fullstandig OH med online manual, F1 support for att anvanda den, och Pop-up hjalp i hela applikationen. Det tredje testet lat testarna losa en uppgift mha antingen pappersmanualerna eller OH, for att se om det var en fordel att anvanda den ena hjalp typen utover den andra. Slutsatsen ar att det ar mojligt att, billigt och relativt enkelt, implementera OH i en redan fardig produkt. Dock sa ar JavaHelp langt fran en perfekt losning och kommer att behova arbetas om for att kunna anvandas kommersiellt. Det ar ocksa mojligt att skapa en online manual fran redan existerande material som Framemaker och Word dokument genom att anvanda programmet RoboHelp.

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Magnetostatic interactions in patterned CoPt films embedded in a permalloy matrix

Applied Physics Letters (2007)

Sven Schnittger S. Dreyer Ch. Jooss S. Sievers U. Siegner

In order to study magnetostatic interactions in magnetic arrays, a two-dimensional pattern of hard magnetic (001) L10 CoPt squares embedded into a permalloy matrix was fabricated. The structural and magnetic properties of these arrays were characterized by magneto-optical measurements, atomic force and magnetic force microscopies. The hard magnetic squares are not exchange coupled to the soft magnet, yet a magnetostatic coupling was observed. This coupling modifies the domain structure of the permalloy matrix. In periodic arrays of embedded CoPt squares, the stray field interaction induces a long-range ordered domain pattern in the soft magnetic matrix and short-range correlations of edge domains in adjacent CoPt squares.

Permalloy

Matrix (chemical analysis)

Micromagnetics

Single domain

10.1063/1.2435592

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Manipulating the dipolar magnetic interactions in FePt square arrays: The role of edge roughness

Journal of Applied Physics (2007)

Jonas Norpoth S. Dreyer Ch. Jooss S. Sievers

The high magnetocrystalline anisotropy energy in hard magnetic materials may sustain magnetization distributions in the remanent state, which exhibit a high number of magnetic surface charges and thus significant magnetic stray fields. Here, we focus onto the stray field distribution in the exterior and the demagnetization field distribution in the interior of hard magnetic FePt elements without and with artificial saw tooth edge roughness. Our experiments and calculations reveal that external stray fields and internal demagnetization fields are considerably modified by the artificial edge roughness.

Magnetocrystalline anisotropy

10.1063/1.2712526

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Straightforward field calculations for uniaxial hardmagnetic prisms: stray field distributions and dipolar coupling in regular arrays

Journal of Physics D Applied Physics (2007)

Jonas Norpoth S. Dreyer Ch. Jooss

Elements of hard- or moderately hardmagnetic materials may exhibit remanent states with a stable uniform magnetization distribution due to the high magnetocrystalline anisotropy energy. In this work, we present analytical calculations of magnetic field distributions arising from appropriate prismatic magnets and apply the results to the special case of hardmagnetic cuboids. The influence of the aspect ratio on the stray field distribution and its range is analysed. Based on these calculations a simple quasi-phase diagram for the emergence of dipolar coupling between individual elements with perpendicular easy axis in regular arrays is derived.

10.1088/0022-3727/41/2/025001

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Citations (14)

Combined optical and force microscopy of patterned magnetic films

Journal of Applied Physics (2006)

S. Sievers M. Albrecht U. Siegner S. Dreyer Ch. Jooss

Combined magneto-optic indicator film (MOIF) and magnetic force microscopy (MFM) is introduced as an advanced tool for the characterization of patterned ferromagnetic films. The MOIF technique combines quantitative stray field imaging of individual micron-sized magnetic elements with a large-area overview of the patterned film while MFM provides nanometer spatial resolution. In order to demonstrate the potential of this approach, lithographically patterned CoPt films with out-of-plane anisotropy were characterized. The large-scale MOIF images reveal variations of the magnetization state and the magnetization reversal among individual magnetic elements. Corresponding high-resolution MFM images relate these results to the micromagnetic configuration of the elements.

Nanometre

Characterization

10.1063/1.2172538

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Citations (7)