Experimentalphysik IV - Nachwuchsgruppe

Junior Research Group Magnetic Microscopy

Our group uses several magnetic imaging techniques like Magnetic-Transmission X-ray Microscopy (MTXM), Photoemission Electron Microscopy (PEEM) or time resolved Kerr Microscopy to study magnetic nanostructures with a high temporal (<230 fs) and a high lateral (<20 nm) resolution. The element-selectivity of synchrotron based methods is especially suited for the characterization of magnetic heterostructures, which are produced and studied by the members of the SFB 491.

The photo shows from left to right: Jie Li, Thomas Eimüller, Wei He, Min-Sang Lee, and Björn Redeker

We built a fs laser scanning Kerr microscope with a temporal resolution <230 fs and a spatial resolution of 210 nm. Equipped with a large temporal and spatial scanning range of 8 ns and 320 um, respectively, it allows studying nonuniform magnetization dynamics on many different time scales over a large area. For demonstration the dynamic Kerr rotation signal of a Fe/Gd multilayer film recorded during the demagnetization process is shown in (a). The signal decreases within 230 fs from 90% to 10% of the signal contrast. A spatial line scan of a sharp edge on a structured Co/Pt multilayer sample reveals a width of 230 nm between 90% and 10% of the signal contrast (b). The spatial and temporal resolution is combined to record a two-dimensional image of the dynamic Kerr response from a Co/Pt dot with a diameter of 200 nm at the delay time of the maximum demagnetization (c).

J. Li, M.-S. Lee, W. He, B. Redeker, A. Remhof, E. Amaladass, C. Hassel, T. Eimüller: Magnetic imaging with femtosecond temporal resolution, Rev. Sci. Instr. 80, 073703 (2009)

A Fe/Gd multilayer has been deposited on SiO₂ nanospheres with a diameter of 800 nm. The magnetization reversal of the resulting nanocaps has been studied by scanning transmission x-ray microscopy (STXM) at the Advanced Light Source (ALS) in Berkeley, USA. A size dependent canges in the magnetic reversal could be found. Caps of 800 nm diameter show S-shaped local hysteresis loops whereas rectangular curves appear for 330 nm caps. This drastic change is attributed to a transition from a radial to an uniaxial magnetization distribution with decreasing diameter. Furthermore, element selective studies reveal a transition from an aligned to a twisted magnetic state with reducing size of the nanocaps.

E. Amaladass, B. Ludescher, G. Schütz, T. Tyliszczak, T. Eimüller: Size dependence in the magnetization reversal of Fe/Gd multilayers on self assembled arrays of nanospheres, Appl. Phys. Lett. 91, 172514 (2007)

The magnetization dynamic of a thermally driven spin-reorientation transition is investigated in an optical pump - x-ray-probe imaging experiment. Excitation of a Fe/Gd multilayer with a fast laser pulse triggers a rotation of the magnetization out of the sample plane. Using x-ray photoemission electron microscopy (X-PEEM) the response of the magnetization is detected with 100 nm spatial resolution. A fast rotation of the anisotropy field is observed, followed by a slow, several nanoseconds lasting relaxation. Interestingly, the anisotropy field relaxes slower than the temperature of the sample.

Read the full story in:

T. Eimüller, A. Scholl, B. Ludescher, G. Schütz, J.-U. Thiele: Slow recovery of magnetic anisotropy following ultrafast optical excitation, Appl. Phys. Lett. 91, 042508 (2007)

This movie shows the magnetization reversal of a Co/Pt multilayer, fabricated and structured by direct pulsed laser interference lithography at the University of Konstanz. The images taken by our full field Kerr microscope at the University of Bochum clearly show the influence of the structuring process on the shape of the domains and the magnetization reversal behaviour.

P. M. Leufke, S. Riedel, M.-S. Lee, J. Li, H. Rohrmann, T. Eimüller, P. Leiderer, J. Boneberg, G. Schatz, M. Albrecht: Two different coercivity lattices in Co/Pd multilayers generated by single-pulse direct laser interference lithography, J. Appl. Phys. 105, 113915 (2009)

Using nanospheres with a diameter of 720 nm, coated with Co/Pt multilayers a reorientation of the magnetization could be observed on a sub-100 nm scale. For more information see:







T. Eimüller, T. C. Ulbrich, E. Amaladass, I. L. Guhr, T. Tyliszczak, M. Albrecht: Spin- reorientation transition of Co/Pt multilayers on nanospheres, Phys. Rev. B. 77, 134415 (2008)

Different hypotheses ranging from adhesive fluids, microsuckers or electrostatic forces have been proposed to explain the mechanism of some animals to adhere to and walk on vertical walls and even on ceilings. We studied the attachment devices of the beetle Gastrophysa viridula and the fly Lucilia caesar using Transmission X-ray Microscopy (TXM) with a lateral resolution of about 30 nm. Results of this study will be published soon in:

T. Eimüller, P. Guttmann, S. N. Gorb: Terminal Contact Elements of Insect Attachment Devices Studied by Transmission X-ray Microscopy, Journal of Experimental Biology 211, 1958 (2008)

Moderator Manfred Breuckmann im Gespräch mit Thomas Eimüller in der Sendung "Zwischen Rhein und Weser", die der WDR 2 am 3.6.2008 sendete. Das Interview kann über den unten angegebenen Link gehört werden:

Ein weiteres Interview mit Thomas Eimüller führte Klaus Deuse für den SWR2. Der Beitrag wurde am 23.07.2008 um 16:05 Uhr in der Sendung Impuls gesendet: "Das Geheimnis der Fliegen - Warum sie an der Decke kleben und was wir daraus lernen können" (siehe unten)

Since September 2008 Thomas Eimüller works as a Professor for physics and electrical engineering at the University of Applied Sciences in Kempten. However, he still supervises the Junior Research Group in Bochum.

This lecture continuous the lecture “Modern Microscopy I” given in WS2006/2007, however, hearing of it is not a precondition to attend and to understand this lecture which will be given in English.

Outline

- electron microscopy (TEM, STEM, SEM, manipulation on the nanoscale,...)
- advanced electron microscopy (PEEM, LEEM, SEMPA,…)
- near field microscopy (SNOM, SNIM,...)
- scanning tunneling microscopy (STM)
- atomic force microscopy (AFM)
- - other local probe methods (CFM, EFM, LFM, MFM, SICM,…)
- microscopy with ions and atoms (including FIB structuring)
- time resolved microscopy
- lensless imaging
- superlenses

Prof. Dr. Thomas Eimüller

Ruhr-Universität Bochum
Institut für Experimentalphysik IV
D-44780 Bochum
Germany

Tel: +49-234-32-23648
Fax: +49-234-32-14173
Room: NB 4 / 130
E-mail: thomas.eimueller(at)rub.de

please replace (at) by @

Hanna Hantusch

Ruhr-Universität-Bochum
Institut für Experimentalphysik IV
D-44780 Bochum
Germany

Tel: (0234) 32 - 23627
Fax: (0234) 32 - 14173