Fig. 6: Sensor for magnetic field and field gradient microscopy.

a Scanning electron microscopy (SEM) top view of the customized cantilever. The receptacle for the subsequent nanowire (NW) attachment is shown in the inset. b SEM micrograph of the magnetic NW attached to the cantilever free end. In the inset, the iron nanowire (FeNW) contained in the carbon nanotube is visible. The diameter \({d}_{{{{{{\rm{Fe}}}}}}}\) of the FeNW and the non-magnetic cap thickness \({t}_{{{{{{\rm{cap}}}}}}}\) are indicated. c SEM side view of the sensor’s free end disclosing the full NW length. The 275 nm gap splits the FeNW into two parts with corresponding lengths \({l}_{{{{{{\rm{Fe}}}}}},1}\) and \({l}_{{{{{{\rm{Fe}}}}}},2}\). d COMSOL beam shape simulations of static bending caused by an applied tip load of \({F}_{z}=-100\) \({{{{{\rm{pN}}}}}}\) and for the 2nd and 5th flexural oscillation modes. The colors describe the absolute value of the deflection. e Magnetic induction (B-field) mapping of a typical iron-filled carbon nanotube (FeCNT) obtained from a phase image reconstructed by off-axis electron holography in the transmission electron microscope. The red iso-lines in steps of π⁄20 display the projected stray-field lines around the FeCNT, which is visualized as greyscale phase image.