Regensburg 2007 – scientific programme
Parts | Days | Selection | Search | Downloads | Help
MA: Fachverband Magnetismus
MA 29: Magnetic Measuring Methods / Sensors / Actuators
MA 29.2: Talk
Thursday, March 29, 2007, 15:30–15:45, H5
Three-dimensional Reconstruction of Magnetic Fields by Electron-Holographic Tomography — •Daniel Wolf1, Petr Formanek1, Hannes Lichte1, and Ann Marie Hirt2 — 1Triebenberg Laboratory, Institute of Structure Physics, Technische Universität Dresden, D-01062 Dresden — 2Institute of Geophysics, ETH-Hönggerberg, CH 8093 Zurich, Switzerland
The phase of an electron wave propagated through a magnetic material represents both the enclosed flux of the magnetic field and the electric potential. Off-axis electron holography combined with tomography allows reconstructing the electron wave in 3 D. At a lateral resolution of about 10nm, we measured the magnetic field in- and outside of magnetite crystals embedded in a magnetotactic bacterium Magnetospirillium gryphiswaldense. Holographic tomography is performed in the following steps: First, we record a tilt series of electron holograms between -60 and +60 degrees in 2 degrees steps. Second, we reconstruct the respective 2D-object exit waves from every electron hologram by usual Fourier analysis. Third, the 3D structure of the phase is built up by weighted back-projection. For separation of the magnetic part from the electric part, we record a second tilt series of the same bacterium magnetized in opposite direction and reconstruct the 3D-wave accordingly. The difference of both 3D-phases contains only the magnetic phase shift produced by the object and, hence, we can determine the three components of the magnetic field. The DFG is kindly acknowledged for funding our Holographic-Tomography project.