Magnetic anisotropy of transition metal based thin films investigated by magnetooptic Kerr effect

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Titel: Magnetic anisotropy of transition metal based thin films investigated by magnetooptic Kerr effect
Autor(en): Kuschel, Timo
Erstgutachter: Prof. Dr. Joachim Wollschläger
Zweitgutachter: Prof. Dr. Mirco Imlau
Zusammenfassung: This thesis presents a study of magnetic anisotropies of transition metal based thin films investigated by magnetooptic Kerr effect (MOKE) and x-ray radiation techniques. Thin Co films of different thickness deposited on glass are investigated to study the uniaxial magnetic anisotropy (UMA) of these films. The direction of the UMA is determined from the azimuthal dependence of the magnetic remanence and differs with increasing thickness of the Co film investigated by x-ray reflectivity (XRR). Strain in the substrate and possible textures in the film structure can be excluded as the origin of the magnetic behavior as studied by grazing incidence wide angle x-ray scattering (GIWAXS). Furthermore, a new combination of different vectorial magnetometry techniques using MOKE is developed (vector MOKE). The processing of the experimental data contains the separation of linear and quadratic parts of the magnetization curves and determination of all three components of the magnetization vector in units of Kerr rotation. The complete reversal process can be reconstructed and interpreted by monodomain states and domain splitting. The measurement procedure and the processing of the data is demonstrated for ultra-thin epitaxial Fe films on MgO(001), which are structurally characerized by XRR and (grazing incidence) x-ray diffraction (GI(XRD)). Magnetic properties of thin Fe films (of different thickness) and A2-type ordered Co50Fe50 films (prepared with different annealing temperatures) on MgO(001) are studied by this new combined vector MOKE technique. Here, a two-domain switching process can be distinguished from a four-domain switching process generated by the incoherent rotation between magnetization saturation and magnetic remanence. Furthermore, UMA constants and domain wall pinning energies are determined using the Stoner-Wohlfarth model. For the Fe films the domain wall pinning energies obtained from these analyses decrease with increasing lateral crystallite sizes determined by GIXRD. For the Co50Fe50 films the domain wall pinning energies decrease with the annealing temperature due to fewer defects in the film. The magnetic structure of a thin B2 ordered Co50Fe50 film reveal two in-plane magnetic easy axes of different strengths which are not orthogonal. This atypical magnetic structure can be explained by a cubic magnetic anisotropy (CMA) induced by the crystalline film structure superimposed by an additional UMA which is not parallel to one of the magnetic easy axes of the CMA.
Schlagworte: MOKE; magnetic anisotropy
Erscheinungsdatum: 7-Dez-2012
Enthalten in den Sammlungen:FB04 - E-Dissertationen

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