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

Abstract

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

Understanding electrostatic and magnetic forces in magnetic force microscopy: towards single superparamagnetic nanoparticle resolution

“…The literature to date lacks evidence for MFM signals from single SPION without applying an external magnetic field. So far, there still is the need for suppression of electrostatic forces which are overlapping and concealing the magnetic signals as well as a need for higher sensitivity due to the comparatively small magnetic interaction [14][15][16][17][18][19]. The atomic force microscopy (AFM) tip is a very sensitive antenna and therefore gives a response to every signal and interaction from inside and outside the system [20].…”

“…Variable voltage in every measurement point can effectively reduce the capacitive coupling and therefore the electrostatic force for heterogeneous samples which is shown by Jaafar et al for magnets of micro scale [14]. Angeloni et al [16] describe an option to distinguish electrostatic and magnetic forces by changing the tip magnetization. In our work we compare different scan modes verifying the theory of the electrostatic forces behavior made by Angeloni et al [15].…”

Magnetic Force Microscopy of in a Polymer Matrix Embedded Single Magnetic Nanoparticles

“…The tip is approximated by a uniform magnetized sphere. Several studies show this model to be a good approximation to calculate the interaction force between the probe and nanoparticles due to the single domain state of the superparamagnetic nanoparticles . Angeloni et al stated the dipole‐dipole model to be a good approximation in case of absence of electro static interaction .…”

“…Several studies show this model to be a good approximation to calculate the interaction force between the probe and nanoparticles due to the single domain state of the superparamagnetic nanoparticles . Angeloni et al stated the dipole‐dipole model to be a good approximation in case of absence of electro static interaction . Thus the phase shift due to the acting force gradient on the tip can be calculated with Equation as follows: where Q is the quality factor of the tip and can be measured during the tip calibration, k is the spring constant of the tip, μ 0 is the vacuum permeability, d is the diameter of the nanoparticle, m p is the magnetic moment of the nanoparticle (Figure S1, Supporting Information), m tip is the magnetic moment of the tip, z is the lift height, and s is the additional distance and is calculated with Equation as follows: where r tip.mag is the magnetic dipole radius of the tip …”

Probing Atomic Level Interactions in Ni Nanorods and Afm Cantilever Using Atomic Force Microscopy Based F–d Spectroscopy

“…The increasing interest in the study and development of magnetic nanomaterials for different technological applications has encouraged development of modern tools and methodology for the characterization and comprehensive understanding of magnetic properties at the nanometer scale [1]. Among these cutting-edge methodologies, magnetic force microscopy (MFM) is widely used for obtaining surface magnetic domain distribution in magnetic materials.…”