The measurements shown here were taken with a Nanosurf Mobile S Large Scan head. The sample was a 10GB single head 3.5" harddisk magnetised in the plane of the medium with a track distance of 600 nm and a bit length of 70 nm, which corresponds to 42k TPI and 363k BPI
The Nanosurf Mobile S and EasyScan 2 (with mode extension) can image the magnetic stray field in the MFM (Magnetic Force Microscopy) imaging mode. In this mode, the stray field is detected by sensing the magnetic force it exerts on a magnetically coated cantilever tip. This force causes a change in the cantilever resonance frequency and thereby shifts the phase of the cantilever vibration. The MFM image is measured by recording the phase contrast image when scanning a plane parallel to the surface in the same location, but a few nanometers away from the sample.