(Color online) Microscopy image of a biosensor chip, showing two narrow giant magnetoresistance sensor strips, flanked by three conducting wires. A cross section of the device and the probe tip is indicated schematically.
(Color online) Height images of two GMR sensor pairs (dim lines) flanked by thick conducting wires (bright), recorded using [(a), (b), and (c)] a sharp tip with bead attached on the side or [(d), (e), (f)] a probe with a fractured tip so the bead touches the surface. Inset: SEM micrograph of tip with bead on cantilever. [(c) and (f)] The simultaneously recorded electrical signal from the magnetic field sensor strip (indicated with arrows), together with model curves for a point dipole and for a spherical volume of independently magnetized dipoles.
Sensor signal, averaged along the strip, recorded at various heights above the sensor. The height increment is .
(Color online) Signal voltage induced in the magnetic sensor by the presence of a bead, both measured (a) and calculated (b), in good agreement. The magnetic field lines are indicated. The geometrically inaccessible region is shaded in (b).
(Color online) Bead magnetic moment (a) and GMR sensor resistance (b) with applied magnetic field. Large and small loops coincide, demonstrating reproducibility.
(Color online) Ratio of peak to valley voltages vs height above the sensor surface, measured for several bead/tip combinations, together with model curves for a point dipole (solid curve) and for a spherical particle of independently magnetized dipoles (dotted). The solid symbols correspond to Fig. 2(f).
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