Domain Wall Dynamics probed by Magneto-Optical-Kerr-Magnetometry


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MÖHRKE, Philipp, 2010. Domain Wall Dynamics probed by Magneto-Optical-Kerr-Magnetometry

@phdthesis{Mohrke2010Domai-9017, title={Domain Wall Dynamics probed by Magneto-Optical-Kerr-Magnetometry}, year={2010}, author={Möhrke, Philipp}, address={Konstanz}, school={Universität Konstanz} }

eng deposit-license Messungen der Domänenwanddynamik mittels Magneto-optischer-Kerr-Magnetometrie Möhrke, Philipp Ferromagnetic nanostructures are a promising candidate for future data storage and logic applications. For this especially the domain walls separating magnetic domains and in particular their manipulation and motion is of interest. Permalloy an alloy of nickel and iron - has been proven to be an ideal model system for this, since the magnetisation configuration can be easily tuned by the sample geometry.<br />This work covers two aspects of domain wall motion in microscopic permalloy nanowires: Firstly, the motion in external magnetic fields and the influence of differently high levels of holmium doping is observed. Secondly, the effects of both local and global heating of the sample structure and their effect on the domain wall motion are probed.<br />For these investigations a focussed magneto-optical Kerr microscope was built. Due to a focus diameter of less than 1µm and the usage of an intense laser source the detection of the motion of individual domain wall in real time is possible. The time resolution reached is below 2ns. Furthermore, the laser allows to alter the sample temperature locally and to probe the domain wall dynamics in this region under the influence of the generated temperature gradients.<br />When doping Permalloy with rare earth metals like holmium the so called Gilbert damping constant alpha rises. By measuring the local velocity distribution of more than one hundred individual domain walls the domain wall velocity if found to drop with increasing alpha. This trend was also predicted by one-dimensional analytical models.<br />The magnetic structures were strongly heated by using high laser intensities and special substrates with a low thermal conductivity. This resulted in high temperature gradients in the order of 100K/µm. Probing the critical pepinning field, which is needed to move a domain wall, for walls positioned within the temperature gradient, a dependence on both the direction and magnitude of the gradient is found. This can be explained by spin currents caused by the temperature gradients (the so called spin-Seebeck-effect). These measurements are completed by directly probing the spin currents utilising the inverse spin-Hall-effect. This opens a new possibility of manipulating domain wall motion as well as generating pure spin currents. 2011-03-24T17:52:52Z Möhrke, Philipp 2011-03-24T17:52:52Z Domain Wall Dynamics probed by Magneto-Optical-Kerr-Magnetometry 2010 application/pdf

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