Spatial and force resolution of magnetic force microscopy in current imaging

Magnetic force microscopy (MFM) can be used to image current distributions in current leads of sub-micron dimensions. Here we present a systematic study about the spatial and force resolution of such currents. In the case of force resolution, we studied the least measurable magnetic force of MFM for different sample currents. The analysis of images from parallel Al conducting plates are combined with those from force-distance curves and finite element calculations. Several interacting regimes between the magnetic tip and the currents are found and interpreted. It is shown that model calculations are necessary even for qualitative image interpretation. Then spatial resolution in the range of 100nm can well be obtained and quantitative studies of current distribution on widths of 10nm resolution are possible in special cases. The approach is demonstrated in imaging the current distribution in superconducting Bi₂Sr₂CaCu₂O _x single crystals. Presented at the VIII-th Symposium on Surface Physics, Třešt’ Castle, Czech Republic, June 28 – July 2, 1999. This work was supported in part by the Swiss Priority Program on Materials. The authors benefited greatly from discussions with D.A. Bonnell, B. Huey and C. Rüegg.