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TY  - THES
AU  - Tillmanns, Andrea
TI  - Magnetisierungsumkehr und -dynamik in Exchange-Bias-Systemen
CY  - Aachen
PB  - Publikationsserver der RWTH Aachen University
M1  - RWTH-CONV-114369
SP  - II, 171 S. : graph. Darst.
PY  - 2005
N1  - Prüfungsjahr: 2005. - Publikationsjahr: 2006
N1  - Aachen, Techn. Hochsch., Diss., 2005
AB  - The present thesis describes magneto-optical analyses of exchange bias thin film systems. Exchange bias (EB) is a unidirectional anisotropy originating from coupling of a ferromagnetic with an antiferromagnetic layer. The magneto-optical Kerr effect (MOKE) allows for detection of the longitudinal (parallel to an external field) as well as the transverse magnetization component (perpendicular to an external field). As shown in this thesis, both measurement can be performed within a single optical setup. Additionally, a magneto-optical pump-probe-setup provides the possibility of studying time-resolved magnetization reversal (on timescales of ps). Here, asymmetric magnetization reversal processes are of special interest. They have only been observed in EB systems and are generally attributed to different reversal mechanisms –  coherent rotation on one side of the hysteresis loop, domain wall nucleation and propagation on the other side. The observed signals can be reproduced with a simulation that deals with the coherent rotation of a single magnetic moment. The shapes of the measured hysteresis loops allow for determination of the angle dependent energy density function of the studied samples. The exchange bias turns out to be the cause for the observed asymmetries. In the second part of this thesis, time-resolved measurements of exchange bias systems show a precession of the magnetization around the effective field after the pump pulse has changed the anisotropies of the sample by means of a local heating. The precession occurs on a timescale of some ten picoseconds. Analysis of the precession frequency depending on the sample orientation again allows the exact determination of the energy density function as well as the anisotropy constants of the particular sample. Finally a method is presented which permits seperation of the longitudinal, transverse and polar (perpendicular to the sample surface) magnetization components. Thus the three-dimensional trajectories describing the precessing magnetic moments can be imaged. In this manner, the time-resolved motions can be displayed in addition to the static ones.
LB  - PUB:(DE-HGF)11
UR  - https://publications.rwth-aachen.de/record/52128
ER  -