A Magnetic and Moessbauer Spectral Study of Core/Shell Structured Fe/Au Nanoparticles

TL;DR

This study synthesizes and characterizes Fe/Au core/shell nanoparticles, revealing complex magnetic and structural properties, including unexpected amorphous alloys and multiple iron oxide components, using advanced diffraction and spectral techniques.

Contribution

It provides a detailed analysis of the magnetic and structural properties of Fe/Au nanoparticles, highlighting their complexity and the presence of unexpected phases.

Findings

Presence of crystalline alpha-iron and gold without oxides

Detection of amorphous Fe1-xBx alloy in Fe core

Complex mixture of iron oxide and paramagnetic components

Abstract

Fe/Au nanoparticles have been chemically synthesized through a reverse micelle reaction and investigated by both conventional and synchrotron based x-ray diffraction and by magnetic and Moessbauer spectral studies. The powder x-ray diffraction patterns reveal both the presence of crystalline alpha-iron and gold and the absence of any crystalline iron oxides or other crystalline products. First-order reversal curves, along with the major hysteresis loops of the Fe/Au nanoparticles have been measured as a function of time in order to investigate the evolution of their magnetic properties. The iron-57 Moessbauer spectra of both uncoated iron nanoparticles and the Fe/Au nanoparticles have been measured at 78 and 295 K and indicate that two major iron containing components are present, namely the expected alpha-iron and the unexpected amorphous Fe1-xBx alloy; several poorly crystallized ordered iron(III) oxide components as well as paramagnetic iron(II) and iron(III) components are also observed. These results indicate that the Fe-core/Au-shell nanoparticles synthesized through reverse micelles are far more complex that had been believed.