Removal of electrostatic artifacts in magnetic force microscopy by controlled magnetization of the tip: application to superparamagnetic nanoparticles

摘要

Magnetic force microscopy (MFM) has been demonstrated as valuable technique for the\udcharacterization of magnetic nanomaterials. To be analyzed by MFM techniques, nanomaterials\udare generally deposited on flat substrates, resulting in an additional contrast in MFM images due to\udunavoidable heterogeneous electrostatic tip-sample interactions, which cannot be easily distinguished\udfrom the magnetic one. In order to correctly interpret MFM data, a method to remove the electrostatic\udcontributions from MFM images is needed. In this work, we propose a new MFM technique, called\udcontrolled magnetization MFM (CM-MFM), based on the in situ control of the probe magnetization\udstate, which allows the evaluation and the elimination of electrostatic contribution in MFM images. The\udeffectiveness of the technique is demonstrated through a challenging case study, i.e., the analysis of\udsuperparamagnetic nanoparticles in absence of applied external magnetic field. Our CM-MFM technique\udallowed us to acquire magnetic images depurated of the electrostatic contributions, which revealed\udthat the magnetic field generated by the tip is sufficient to completely orient the superparamagnetic\udnanoparticles and that the magnetic tip-sample interaction is describable through simple models once\udthe electrostatic artifacts are removed.