Zeit- und ortsaufgelöste Beobachtung von Magnetisierungsdynamik unter Verwendung von "Spin-polarized low energy microscopy" (SP-LEEM)

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We will exploit the magnetisation dependence of the backscattering cross section of spin-polarised electrons providing both a high intensity of reflected electrons and a high asymmetry. Using an emission electron microscope we are able to image magnetic domains with high lateral resolution of better than 25 nm. A basic advantage of the technique is that it combines the highly resolving magnetic imaging with structural imaging including even the visibility of single monoatomic steps on surfaces. Time resolution is implemented by a stroboscopic illumination of the sample by a pulsed electron beam which in turn is produced by shining a pulsed laserbeam from a laserdiode on a GaAs-photocathode. The time resolution is limited by the pulse length of the electron beam pulse. Ultrafast magnetisation dynamics will be initiated in the sample either by application of field pulses using the strip-line technique or heating pulses using a Ti-sapphire laser. We will investigate single crystalline ultrathin magnetic films prepared by molecular beam deposition in situ in UHV. Strip-lines are lithographically prepared on a sapphire(11-20) substrate from a single crystalline Mo(110) film. The strip-line surface will be cleaned in UHV applying oxygen - anneal/flash cycles in order to allow for an epitaxial growth of ultrathin Co and Fe films. The dynamical magnetisation process will be investigated as a function of the time delay between field and/or heating pulse with respect to the electron probe pulse.