Observation of the effects of tip magnetization states on magnetic force microscopy images

We have investigated the effect of the orientation between the tip and the tip-magnetizing field on the subsequent magnetic force microscopy images. We have observed that commonly used CoCr coated tips have a component of the remanent magnetization pinned parallel to the tip axis. In order to study the pinned component of the tip, saturating fields were applied at various angles relative to the tip axis. Each time the tip was magnetized, we imaged a hard disk sample that had lithographically patterned landmarks designed to allow us to find, image, and compare images of the same nanometer-sized magnetic feature. We have also observed a component of the tip magnetization that is free to rotate dynamically due to the stray magnetic fields of the sample being imaged. To study this effect, an external bias field was applied parallel to the tip axis while imaging. This field effectively pinned the tip magnetization. With these techniques, we are thus able to compare two effects of tip magnetization on magnetic force microscope images. [S0021-8979(99)42708-2].