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MA: Fachverband Magnetismus
MA 22: Magnetic Measurement Methods
MA 22.2: Vortrag
Dienstag, 15. März 2011, 11:15–11:30, HSZ 403
Noise characteristics of magnetoresistive fluxgates for weak magnetic field sensing — •Leoni Breth1,3, Theodoros Dimopoulos1, Rudolf Heer1, Jörg Schotter1, Karsten Rott2, Dieter Süss3, and Hubert Brückl1 — 1AIT Austrian Institute of Technology GmbH, Nano Systems, 1220 Vienna, Austria — 2University of Bielefeld, Physics Department, Germany — 3Vienna University of Technology, Solid State Physics Department, Austria
Magnetic tunnel junctions (MTJs) with MgO barriers are known for their high magnetoresistance (MR) ratio, which makes them possible candidates for measuring weak biomagnetic fields stemming from the human heart or brain activity. Today's established sensors for magneto-cardio and encephalogram employ costly SQUID systems. To make MTJ sensors competitive to SQUIDs, their detectivity, which is limited by their intrinsic noise level - especially in the low frequency range- has to reach the sub-nT regime. To this end, several designs have been proposed (e.g. integration of flux concentrators). Here, we introduce an alternative technique, inspired from fluxgate magnetometers, employing lock-in amplification. An alternating magnetic field that is produced by a current line is used to switch the free layer of the MTJ. The presence of a weak DC or low frequency magnetic field generates a second harmonic component in the MR signal of the MTJ, which is a linear measure for the magnetic field strength. We present the low frequency noise characteristics of MgO-based MTJs and discuss their influence on the magnetic field detectivity of the proposed MR fluxgate design.