Origin of reduced magnetization and domain formation in small magnetite nanoparticles

Abstract

The structural, chemical, and magnetic properties of magnetite nanoparticles are compared. Aberration corrected scanning transmission electron microscopy reveals the prevalence of antiphase boundaries in nanoparticles that have significantly reduced magnetization, relative to the bulk. Atomistic magnetic modelling of nanoparticles with and without these defects reveals the origin of the reduced moment. Strong antiferromagnetic interactions across antiphase boundaries support multiple magnetic domains even in particles as small as 12–14 nm.

Internal Structure and Magnetic Properties in Cobalt Ferrite Nanoparticles: Influence of the Synthesis Method

“…Conversely, in the solvent‐controlled SV synthesis one would not expect such preferred growth and spherical NPs predominate. Such lack of specificity in the growth of the crystal faces can cause local structural defects when different crystallographic directions match, which are in agreement with the small increase in the lattice parameter of SV NPs compared to the bulk value, and with the slightly lower D XRD / D TEM values observed for SV NPs compared to TD samples. On the other hand, the lower lattice parameters of CP and AC NPs suggest a different origin that is more likely to be associated to the crystalline disorder, evidenced by a strong decrease in the D XRD / D TEM ratio.…”

“…At low temperature, M R / M S reaches a maximum of 0.77 for TD9 and a minimum of 0.47 for AC10, as reported in Table 2 together with the main parameters of the magnetic analysis. Multiple factors have been proposed to explain the variation in the magnetic properties of NPs with analogous composition and size, and its origin is still under debate. In the following sections we will explore the interplay between several factors responsible for the main magnetic features evidenced in Figure .…”

“…However, in spite of those advances, a broad variation of the NPs' magnetic properties is usually found, even for NPs with similar size and composition . Such broad dispersion has been typically ascribed to the presence of size and shape distributions, stoichiometry gradients, interparticle interactions, and structural defects, which depend strongly on the synthesis procedure and whose contribution is difficult to identify .…”

“…In this line, some recent results highlight that NP systems in reality are more complex than what was thought, even in the case of highly crystalline, monodisperse and non‐interacting ensembles of NPs. For example, advanced TEM studies performed on Fe 3 O 4 NPs revealed that the density of antiphase boundaries resulting from different synthesis procedures can be responsible for a considerable reduction in the magnetic moment; and single‐particle experiments performed on Fe NPs showed recently that the magnetic properties can be significantly affected by metastable lattice defects …”

Fabrication of CNT/ION hybrids and their impact on the biomedical applicability of PCL‐based composite films

“…When compared with magnetic properties of bulk magnetite (92 emu/g), the obtained M s values of synthesized particles were lower than expected. This result could origin either from the presence of maghemite phase or various structural defects of the nanoparticles, such as surface disorder, broken translational symmetry, and antiphase domain boundaries . Despite the presence of the defects, both of the prepared hybrids and the pIONs could be described as ferrimagnetic materials with low value of coercivity (H c ).…”