Modelling the perturbative effect of MFM tips on soft magnetic thin films

The significant current interest in magnetic force microscopy has raised a question on the use of such instruments to image magnetically soft materials, The magnetically hard MFM tip may alter the magnetisation distribution in soft samples such as permalloy. Previous work has shown that this problem can be alleviated by using a thin film coated tip with reduced magnetic volume. This work uses a micromagnetic model to examine quantitatively the perturbative effect of an MFM tip on a soft sample. It is shown that MFM tips can in some cases lead to significant changes in the sample magnetisation distribution of up to 60% of saturation in the worst case, and typically 10-30%. Importantly, small perturbations in the magnetisation distribution are possible without obvious effects on the MFM image contrast, but which may affect the ability to produce quantitative measurements.