Remote sensing of nanoscale displacements through detection of magnetic field gradients with magnetic tunnel junction sensors

An array of magnetic tunnel junctions, connected in a Wheatstone bridge is characterized as a positioning sensor to detect spatial displacement of a magnetized object. In order to perform the experiment, the sensor was mounted at a fixed frame, and a micro-magnet was installed on top of nano-positioning stage. The movement of the stage was controlled by stepper motor and piezo-actuator in closed-loop feedback. The sensor signal was recorded in real time, to detect displacement of the magnet, defined by commands to the stage. The positioning transfer curves were obtained for different magnetization orientations of the magnet with respect to the field sensing direction of the MTJs and positioning direction of the magnet displacement. For the optimal configuration, giving linear transfer curve between positioning displacements and the sensor voltage, the effects of magnet size, sensor size and vertical distance between the sensor and magnet positioning trajectories, are characterized. In the optimized configuration, 10 nm steps resolution is obtained.