Magnetic scanning gate microscopy of a domain wall nanosensor using microparticle probe

• AFM tips with a magnetic bead attached used to test interaction with domain wall.
• Domain wall inside a nanostructure affect the electrical resistance.
• Recording electrical resistance while scanning with modified AFM probe.
• Change of resistance as a function of the position of the magnetic bead.
• This allows comparing different devices in a reproducible and controllable way.

We apply the magnetic scanning gate microscopy (SGM) technique to study the interaction between a magnetic bead (MB) and a domain wall (DW) trapped in an L-shaped magnetic nanostructure. Magnetic SGM is performed using a custom-made probe, comprising a hard magnetic NdFeB bead of diameter 1.6 µm attached to a standard silicon tip. The MB–DW interaction is detected by measuring changes in the electrical resistance of the device as a function of the tip position. By scanning at different heights, we create a 3D map of the MB–DW interaction and extract the sensing volume for different widths of the nanostructure's arms. It is shown that for 50 nm wide devices the sensing volume is a cone of 880 nm in diameter by 1.4 µm in height, and reduces down to 800 nm in height for 100 nm devices with almost no change in its diameter.