Reversible and irreversible temperature-induced changes in exchange-biased planar Hall effect bridge (PHEB) magnetic field sensors.

G. Rizzi, N.C. Lundtoft, F.W. Østerberg, M.F. Hansen
Technical University of Denmark, DK

Keywords: magnetic, biodetection, exchange-bias, temperature, reversible, irreversible


We generally investigate the use of exchange-biased planar Hall effect bridge (PHEB) magnetic field sensors for biodetection, where the sensors detect the binding and unbinding of magnetic beads to the sensor surface by biomolecular interactions. The thermal stability of the sensors is critical when these are used for characterizing the melting of DNA duplexes at temperatures up to 90°C as well as for understanding the influence of elevated temperatures on the behavior of exchange-biased thin films. In this work we study the changes of PHEB sensors upon exposure to temperatures between 25°C and 90°C. From analyses of the sensor response vs. magnetic fields applied between ±40 mT, we extract the exchange bias field Hex, the uniaxial anisotropy field Hk and the anisotropic magnetoresistance (AMR) at a given temperature and by comparing measurements carried out at elevated temperatures T with measurements carried out at 25°C after exposure to T, we can separate the reversible from the irreversible changes of the sensor.