This thesis deals with the magnetization dynamics in nanostructures of NiFe alloys (Ni80Fe20 and Ni20Fe80) induced by an electric current via the spin transfer torque effect (STT). Single-pulse and time-resolved experiments have been carried out, imaging the magnetic domains in a photoemission electron microscope (PEEM), using the circular polarized synchrotron radiation of BESSY-II. In single-pulse experiments, the reaction of magnetic domains and domain walls (DWs) upon individual current pulses in the nanostructures are studied and the approximate threshold current density for the DW motion was determined to about 7.5 x 1011 A/m2. We designed three different types of nanostructures, favorable for different types of DWs: a V-shape, a half ring-shape and a notched half ring- shape. Besides the influence of the current pulses on domain textures, we observed that high current pulses created new multiple domain configurations, like diamond patterns and domain arrays. For those, rather than nucleation due to STT, a temperature rise seems to be the dominant mechanism. We also observed the conversion from a vortex-like flux closure domain into a transverse wall (TW). In order to enable time-resolved studies of the DW motion in pump-probe experiments with sufficient intensity, several modifications for a time-resolving mode had to be integrated into our energy filtered aberration-corrected PEEM: (1) A new modified sample holder for shorter current pulses ( ∼ 1 ns). (2) A negative deflection-gating concept to increase the intensity while discriminating the signal from all the multi-bunches (MBs) with no adjacent pump pulse. Finally, we performed a pump-probe experiment and have observed the dynamics of small reversible DW boundary changes on a ns timescale for the first time in a truly current-induced pump-probe experiment.
Muhammad Ishfaq Khan (Mon,) studied this question.