Analysis of magnetic bit pattern by magnetic force microscopy

Abstract

This paper describes the behavior of a tiny tip of the magnetic force microscope (MFM) over longitudinally directed magnetic bits, by a quantitative approach. Three possible magnetic structures are taken into consideration together with a realistic tip model. Magnetic and van der Waals interactions between the tip and the sample are derived analytically to simulate a force and a force gradient in the MFM. Contours of constant force gradient are presented and related to the known experimental data. The important role of van der Waals force gradient in constant force gradient measurements is shown. The force gradient from a magnetic interaction is partly negative and partly positive, it is balanced or increased by the always positive van der Waals force gradient. Asymmetry of the force gradient above the transition area is revealed when the MFM tip is tilted. By tilting the tip, the detection of two components of a stray field is performed. Lateral resolution of 90 nm could be achieved with our realistic tip model.