Magnetic scanning gate microscopy of graphene Hall devices (invited)

We have performed sensitivity mapping of graphene Hall devices with the width of 0.6–15 μm operating in the diffusive regime under non-uniform, local magnetic and electric fields induced by a scanning metallic magnetic probe. The transverse voltage was recorded, while tuning the magnitude and orientation of the bias current, the probe-sample distance, and orientation of the probe magnetization. A strong two-fold symmetry pattern has been observed, as a consequence of capacitive coupling between the probe and the sample. The effect is particularly pronounced in small devices (<1 μm), where the dominating electric field contribution significantly lowers the effective area of the magnetic sensor. We show that implementation of the Kelvin probe feedback loop in the standard scanning gate microscopy setup drastically reduces parasitic electric field effects and improves magnetic sensitivity.