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978-3-86853-783-3, Reihe Physik
Tjark Florian Windisch
Magnetic investigations on correlated electrons in a pseudo-spin-system and ferromagnetic / nanomechanical hybrid systems
142 Seiten, Dissertation Technische Universität München (2010), Softcover, A5
In the course of this work a fiber optical cantilever magnetometer with a 4 axis piezo based positioning system was designed and set up. The positioning system is based on the slip-stick principal and included movement in xyz and angle α direction. We performed simulations to understand the reflectivity evolution while scanning the sample with respect to the glass fiber of our detection setup.
To measure the magnetization of AlAs quantum wells we used a capacitive read out cantilever magnetometer. These AlAs quantum wells exhibit a twofold valley degeneracy. We performed intensive studies on the angular dependence of the magnetization with respect to the external magnetic field which revealed a strong electron-electron interaction and a lifting of the valley degeneracy even for angles of α → 0 and therefore an intrinsic crossing of the energy levels. In addition we performed temperature dependent studies which revealed strongly enhanced energy gaps and a temperature dependence that does not even qualitatively match to the expectations including commonly assumed many body effects.
In the second part of this work we investigated on the mechanical and magnetic properties of nanomechanical bridges. These bridges with a width of 120 nm a length of 2 μm and a thickness of roughly 150 nm were prepared by focused ion beam etching into the inner conductor of a coplanar wave guide. We performed GHz spectroscopy measurements in the time and frequency regime. We were able to measure the ultra high resonance frequency of the nanobridge in the order of 0.5 GHz. The excitation power dependent measurements indicate a mechanical resonance oscillation.