Unraveling nanoscale magnetic ordering in Fe3O4 nanoparticle assemblies via x-rays

TL;DR

This study uses x-ray resonant magnetic scattering to reveal how magnetic correlations vary with particle size in Fe3O4 nanoparticle assemblies, impacting their potential nanotechnological applications.

Contribution

It demonstrates size-dependent magnetic ordering in Fe3O4 nanoparticles using XRMS, providing insights inaccessible to standard magnetometry techniques.

Findings

Smaller particles exhibit magnetic disorder and superparamagnetic behavior.

Larger particles show strong magnetic correlations, including ferromagnetic and anti-ferromagnetic orders.

Magnetic correlations depend on particle size and are present even in sparse assemblies.

Abstract

: Understanding the correlations between magnetic nanoparticles is important for nanotechnologies, such as high-density magnetic recording and biomedical applications, where functionalized magnetic particles are used as contrast agents and for drug delivery. The ability to control the magnetic state of individual particles depends on the good knowledge of magnetic correlations between particles when assembled. Inaccessible via standard magnetometry techniques, nanoscale magnetic ordering in self-assemblies of Fe3O4 nanoparticles is here unveiled via x-ray resonant magnetic scattering (XRMS). Measured throughout the magnetization process, the XRMS signal reveals size-dependent inter-particle magnetic correlations. Smaller (5 nm) particles show little magnetic correlation, even when tightly close-packed, yielding to mostly magnetic disorder in the absence of external field, which is characteristic of superparamagnetic behavior. In contrast, larger (11 nm) particles tend to be strongly correlated, yielding a mix of magnetic orders including ferromagnetic and anti-ferromagnetic orders. These strong magnetic correlations are present even when the particles are sparsely distributed.