High sensitivity SQUID magnetometer / AC susceptometer

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Magnetic parameters such as the magnetic moment and the magnetic susceptibility play a fundamental role in the study and characterization of magnetic materials. With the SQUID magnetometer applied for here, the magnetic properties of thin magnetic films and magnetic heterostructures, ensembles of magnetic clusters or molecular magnets, as well as superconducting layers shall be investigated. An important part of the research work envisaged hereby aims at samples with ferrimagnetic or antiferromagnetic properties. These samples typically feature very small (net) magnetic moments, which can only be resolved with a highly sensitive, state-of-the-art magnetometer. More specifically, we want to use magnetometry measurements to quantitatively study the evolution of the magnetic moment as a function of magnetic field strength, magnetic field orientation and temperature. In addition to quantifying the saturation moment, the remanent moment and the magnetic coercive fields, such experiments also provide important insights into the magnetization reversal process and the magnetic anisotropy of the samples. Detailed knowledge about these magnetic properties is important for optimizing sample preparation processes, and for analyzing and interpreting measurement data acquired in other experiments. In addition, we want to use the possibility of recording magnetotransport and magnetization data simultaneously in one and the same sample in one and the same setup, in order to investigate the interplay between magnetic properties and magnetoresistive response, e.g. in the Verwey transition in magnetite, or in the anomalous or topological Hall effect in ferromagnets and antiferromagnets. Finally, in addition to magnetometry, we intend to use AC magnetic susceptibility measurements to quantify magnetic ordering temperatures and the existence and range of different magnetic phases. Since the imaginary part of the susceptibility is directly linked to magnetic dissipation, AC susceptibility measurements can also provide important information for the analysis of magnetic fluctuation phenomena, which currently are being studied by several groups within at the University of Konstanz.