Detection of superparamagnetic markers with GMI-sensors

Giant magnetoimpedance (GMI) describes the strong dependence of the impedance of soft magnetic microwires or thin film systems on the presence of a small external magnetic field. The change of the impedance can be in the order of several hundred percent. Numerous applications have been proposed or are employed, e. g. the measurement of extremely low magnetic fields. As thin film structures are better suited for assembly and integration than wires, we have focused on the development and characterization of thin film structures. The sensors consist of FeCuNbSiB/Cu/FeCuNbSiB thin film trilayer systems. In these structures, the difference between the longitudinal and the transversal and polar MI-effects is very large as compared to GMI-wires. We discuss different approaches to measure the GMI and we show that small amounts of superparamagnetic particles can be detected.