Direct evidence for an interdiffused intermediate layer in bi-magnetic core-shell nanoparticles.

Amélie Juhin,Marcin Sikora,Josep Nogués,Sònia Estradé,Pieter Glatzel,Claire Carvallo,Alberto López-Ortega,Maria Dolors Baró,Francesca Peiró,Philippe Sainctavit,Marta Estrader

doi:10.1039/c4nr02886d

Abstract

Core-shell nanoparticles attract continuously growing interest due to their numerous applications, which are driven by the possibility of tuning their functionalities by adjusting structural and morphological parameters. However, despite the critical role interdiffused interfaces may have in the properties, these are usually only estimated in indirect ways. Here we directly evidence the existence of a 1.1 nm thick (Fe,Mn)3O4 interdiffused intermediate shell in nominally γ-Fe2O3-Mn3O4 core-shell nanoparticles using resonant inelastic X-ray scattering spectroscopy combined with magnetic circular dichroism (RIXS-MCD). This recently developed magneto-spectroscopic probe exploits the unique advantages of hard X-rays (i.e., chemical selectivity, bulk sensitivity, and low self-absorption at the K pre-edge) and can be advantageously combined with transmission electron microscopy and electron energy loss spectroscopy to quantitatively elucidate the buried internal structure of complex objects. The detailed information on the structure of the nanoparticles allows understanding the influence of the interface quality on the magnetic properties.

Highlights

In recent years core–shell (CS) nanoparticles have become increasingly appealing to develop efficient ways to stabilize, functionalize and improve the properties of single-phaseGiven the critical role of the CS morphology, the constituting materials and their interface in establishing the nal properties of the nanoparticles, the precise determination of these parameters is crucial for the understanding and ne tailoring of the functionalities of CS systems
Structural and morphological characterization The CS nanoparticles were synthesized by a seeded-growth approach, where a Mn-oxide layer was grown on pre-synthesized Fe-oxide nanoparticles
The structural characterization of the CS nanoparticles using Fast Fourier Transform, High-resolution transmission electron microscopyPaper (HR-TEM) (ESI Fig. S2a and b†) and powder X-ray diffraction (ESI Fig. S2c†) reveals the presence of a cubic spinel phase, which is compatible with magnetite Fe3O4 or maghemite g-Fe2O3.43 a tetragonal spinel phase is observed, which can be assigned to Mn3O4 or g-Mn2O3 and whose relative proportion is small with respect to the cubic phase

Summary

Introduction

Given the critical role of the CS morphology (i.e., core diameter, shell thickness and shape), the constituting materials and their interface in establishing the nal properties of the nanoparticles, the precise determination of these parameters is crucial for the understanding and ne tailoring of the functionalities of CS systems. This type of characterization is far from simple and o en it is only the combination of several characterization techniques that allows solving the CS internal structure. Valuable internal information can be obtained from so XAS-XMCD measurements in transmission for sufficiently thin, homogenous structures,[37] and even using total electron yield detection by a thorough and careful analysis procedure.[38]

Methods

Results

Conclusion