Single nanoparticles magnetization curves by controlled tip magnetization magnetic force microscopy

Abstract

The development of high spatial resolution and element sensitive magnetic characterization techniques to quantitatively measure magnetic parameters of individual nanoparticles (NPs) and deeply understand and tune their magnetic properties is a hot topic in nanomagnetism. Magnetic force microscopy (MFM), thanks to its high lateral resolution, appears as a promising technique for the magnetic characterization of single nano-sized materials although it is still limited by some drawbacks, especially by the presence of electrostatic artifacts. Recently, these limitations have been overcome by the development of a particular MFM based technique called controlled magnetization - MFM (CM-MFM) allowing, in principle, a quantifiable correlation between the measured magnetic signal and the magnetization of the object under investigation. Here we propose an experimental procedure, based on the use of CM-MFM technique, to measure the magnetization curve of single magnetic NPs individuating their saturation magnetization, magnetic field, and coercivity. We measured, for the first time, the magnetization curves of individual FeO nanoparticles with diameters in the range of 18-32 nm by using a MFM instrument. Results are in very good agreement with the quantitative data obtained by SQUID analysis on a macroscopic sample, showing the high potential of the technique in the field of nanomagnetometry.

Magnetic force fields of isolated small nanoparticle clusters

“…This two-dipole model has been successfully applied for extracting quantitative magnetic information, particularly on nanostructures able to generate field geometries similar to those used for the tip calibration [56][57][58] . Accordingly, spherical NPs with known magnetization have been employed to calibrate the magnetic tips, which were subsequently used to determine the magnetic moment of other spherical NPs or clusters 58,59,63 .…”

“…SI5). This analysis is a necessary step towards obtaining a quantitative information about the magnetic moment of clusters 58,59 . It is worth noting that the diameters of the NPs have been estimated from height profiles and not from lateral sizes, as lateral dimensions are usually overestimated by tip convolution effects 59 .…”

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

“…The additional forces can often lead to a misleading interpretation of measured MFM data [21]. The aim of this work is to theoretically and experimentally prove that the mirroring of the topography often seen in MFM phase shift while imaging nanoparticles [5,15,19,22] is due to capacitive coupling between tip and substrate. Understanding this effect this work aims at decreasing the capacitive coupling in order to magnetically visualize single SPIONs.…”

Identification of nanoparticles and nanosystems in biological matrices with scanning probe microscopy

“…With the advent and the development of nanotechnology, MFM techniques found wider application in the characterization of several kinds of new magnetic nanomaterials, such as NPs (Häberle et al, 2012;Neves et al, 2010;Schreiber et al, 2008;Sievers et al, 2012), nanodots (Pei et al, 2011), nanotubes and nanowires (Jaafar et al, 2011;Tabasum et al, 2014). Furthermore, some recently developed MFM-based techniques allows not only the imaging and the qualitative verification of the magnetic character of the studied nanomaterials, but also, through the analysis of the magnetic contrast, the quantitative determination of some parameters of interest, such as the magnetization curve of single NPs, that is, the saturation magnetization and magnetic field and the coercivity, by performing in-field measurements (Angeloni et al, 2017), or the nonmagnetic coating thickness of core-shell magnetic NPs (Angeloni et al, 2016).…”