Structure–Redox–Magnetism Dynamics Induced by Pd–Fe Interaction in Mixed Iron Oxide Nanoparticles

Abstract

Abstract The incorporation of noble metals into iron oxide nanomaterials represents an effective strategy to tailor their redox and structural properties through metal-oxide interactions. However, a detailed experimental understanding of these effects is limited. This work investigates the impact of Pd incorporation and Ag perturbation in mixed iron oxide nanoparticles by combining bulk- and surface-sensitive techniques. X-ray absorption spectroscopy (XAS) shows that Pd significantly enhances iron reducibility. Accordingly, wavelet transform analysis of the EXAFS region further provides evidence of Fe–Pd interactions, indicating nanoscale proximity between Pd and Fe atoms. These bulk-sensitive results are complemented by X-ray photoelectron spectroscopy (XPS), which reveals an increased fraction of reduced Fe species at the nanoparticle near surface upon Pd incorporation. In situ grazing-incidence X-ray diffraction (GI-XRD) during heat treatment under H2 provides insight into the evolution of these effects, showing (i) suppression of the hematite minor phase already after Pd impregnation and (ii) magnetite major phase lattice expansion during H2 treatment, both occurring exclusively in the presence of Pd. Complementary XPS analysis indicates partial migration of Pd into the iron oxide lattice under H2 treatment, contributing to the oxide lattice expansion beyond that of iron reduction alone. Magnetic measurements reveal an overall magnetization increase upon Pd incorporation, with a nonlinear dependence on Pd loading reflecting the balance between enhanced iron reducibility and lattice disorder. Finally, Ag incorporation slightly increases the fraction of reduced Fe species but strongly alters the magnetic response, consistent with an additional bimetallic perturbation arising from Pd–Ag coexistence.