SAXS Analysis of Magnetic Field Influence on Magnetic Nanoparticle Clusters

Abstract

In this work, we investigated the local colloidal structure of ferrofluid, in the presence of the external magnetic field. The nanoparticles studied here are of the core-shell type, with the core formed by manganese ferrite and maghemite shell, and were synthesized by the coprecipitation method in alkaline medium. Measures of Small Angle X-ray Scattering (SAXS) performed in the Brazilian Synchrotron Light Laboratory (LNLS) were used for the study of the local colloidal structure of ferrofluid, so it was possible to study two levels of structure, cluster and isolated particles, in the regimes with and without applied magnetic field. In the methodology used here there is a combination of the information obtained in the system with and without magnetic field application. In this way, it is possible to undertake a better investigation of the colloidal dispersion. The theoretical formalism used: (i) the unification equation proposed by Beaucage G.; (ii) the analysis of the radial distribution function p ( r ) and (iii) theoretical calculation of the radius of gyration as a function of the moment of inertia of the spherical of n-nanoparticles.

Fabrication of Mn1Zn Fe2O4 ferrofluids from natural sand for magnetic sensors and radar absorbing materials

“…Specifically, the fitting analysis results of the SAXS data for the Mn 1 -x Zn x Fe 2 O 4 ferrofluids are presented in Table 2 . The primary particles of the Mn 1 -x Zn x Fe 2 O 4 ferrofluids were spherical, with a diameter of 3.6–4.1 nm that formed secondary cluster particles, which is similar to the results of a previous work [ 30 ]. The primary particle building blocks constructed a fractal structure with a chain-like structure for all samples with a fractal dimension from 1.12 to 1.67.…”

Lattice Strain of Zn-Mn Mixed Ferrite Nanocrystals in a Core-Shell Morpho-Chemical Structure

“…In addition, the absence of subproducts from the synthesis steps corroborates the results which are obtained from X-ray diffractogram analysis, as we discuss in next section. Also, we observe that the particles present a strong tendency to aggregate, which is due to magnetic dipolar interactions between them 52,65 .…”

“…A first look at TEM micrographs (Figures 2A, 2B, 2C, and 2D) allows us to conclude that most of the particles are approximately round and homogeneous, i.e., the particles do not present holes or discontinuities.In addition, the absence of subproducts from the synthesis steps corroborates the results which are obtained from X-ray diffractogram analysis, as we discuss in next section. Also, we observe that the particles present a strong tendency to aggregate, which is due to magnetic dipolar interactions between them52,65 .For all samples investigated, we measure the diameter of ~ 600 non aggregated NPs to obtain its size distribution. The obtained histograms (see Figures2E and 2F) present a size distribution profile well-fitted by a log-normal probability…”

Ferrofluids and bio-ferrofluids: looking back and stepping forward

“…Thus, “colloidal” anisotropies presumably originating from the competition between steric repulsion and magnetostatic attraction were evidenced by magnetometry and SANS in the case of diluted bio-ferrofluids having dextran coated magnetite NPs with 44 ± 13 nm mean core size. 354 The magnetic field induced anisotropy of cluster solutions (manganese ferrite with a maghemite shell in water, particle size of about 7 nm, pH = 2, volume fraction of 2%), which satisfy good superparamagnetic behavior, was recently observed 355 by 2D SAXS and related to the anisotropic secondary aggregation of the magnetized clusters. The existing residue after the anisotropic aggregate preparation explains the anisotropic growth of clusters in magnetic fields even in ferrofluids with weak particle interaction, which is reflected well in 2D SAXS patterns.…”