We have built a scanning probe microscope where a magnetoresistive (MR) head is used as the sensing element. The sensor region of the MR head is about 5 μm wide and 30 nm thick giving high resolution in one direction and poor resolution in the other. As MR heads with smaller cross-track dimensions are developed, submicron resolution in this direction should also be realizable. The MR head is mounted on a piezoelectric bimorph and vibrated perpendicular to the plane of the sample, and the ac voltage output of the head is detected with a lock-in amplifier. We have imaged pre-recorded bits as a function of scan height, and also imaged bits that were written using the write element of the same MR head. The typical voltage change through a transition is ∼4 μV, two orders of magnitude smaller than signals generated on a spin stand. This is most likely due to the difficulty in setting the slider parallel to within submilliradian accuracy to the plane of the sample. Our positioning system does not have this capability at this time. With modifications in the positioning stage, this device should provide a valuable tool for investigating the recording and playback processes, and for characterizing media and heads at ever decreasing track widths, bit separations, and flying heights.

O’Barr, R., Lederman, M., & Schultz, S. (1996). A scanning microscope using a magnetoresistive head as the sensing element. Journal of Applied Physics, 79(8), 6067–6069.