Magnetic Study of CuFe2O4-SiO2 Aerogel and Xerogel Nanocomposites.

Alizé Gaumet,Anna Corrias,Francesco Caddeo,Danilo Loche,Alberto Casu,Maria Casula,Andrea Falqui

doi:10.3390/nano11102680

Abstract

CuFe2O4 is an example of ferrites whose physico-chemical properties can vary greatly at the nanoscale. Here, sol-gel techniques are used to produce CuFe2O4-SiO2 nanocomposites where copper ferrite nanocrystals are grown within a porous dielectric silica matrix. Nanocomposites in the form of both xerogels and aerogels with variable loadings of copper ferrite (5 wt%, 10 wt% and 15 wt%) were synthesized. Transmission electron microscopy and X-ray diffraction investigations showed the occurrence of CuFe2O4 nanoparticles with average crystal size ranging from a few nanometers up to around 9 nm, homogeneously distributed within the porous silica matrix, after thermal treatment of the samples at 900 °C. Evidence of some impurities of CuO and α-Fe2O3 was found in the aerogel samples with 10 wt% and 15 wt% loading. DC magnetometry was used to investigate the magnetic properties of these nanocomposites, as a function of the loading of copper ferrite and of the porosity characteristics. All the nanocomposites show a blocking temperature lower than RT and soft magnetic features at low temperature. The observed magnetic parameters are interpreted taking into account the occurrence of size and interaction effects in an ensemble of superparamagnetic nanoparticles distributed in a matrix. These results highlight how aerogel and xerogel matrices give rise to nanocomposites with different magnetic features and how the spatial distribution of the nanophase in the matrices modifies the final magnetic properties with respect to the case of conventional unsupported nanoparticles.

Highlights

IntroductionSpinel ferrite nanoparticles with general formula MFe2 O4 (where M is a bi-valent transition metal ion such as Mn2+ , Ni2+ , Co2+ , Cu2+ , Zn2+ , etc.) have been the object of intense investigation due to their interesting optical, magnetic and catalytic properties for their potential application in storage devices [1], photo-catalysis [2], magnetic fluids [3], sensors [4] and biomedicine [5]
Spinel ferrite nanoparticles with general formula MFe2 O4 have been the object of intense investigation due to their interesting optical, magnetic and catalytic properties for their potential application in storage devices [1], photo-catalysis [2], magnetic fluids [3], sensors [4] and biomedicine [5]
As previously found in the sol-gel synthesis of other ferrites dispersed in silica aerogels [30], iron is very likely present in the form of ferrihydrite, whose peaks are hidden within the amorphous silica background because of the poor crystallinity of this phase

Summary

Introduction

Spinel ferrite nanoparticles with general formula MFe2 O4 (where M is a bi-valent transition metal ion such as Mn2+ , Ni2+ , Co2+ , Cu2+ , Zn2+ , etc.) have been the object of intense investigation due to their interesting optical, magnetic and catalytic properties for their potential application in storage devices [1], photo-catalysis [2], magnetic fluids [3], sensors [4] and biomedicine [5]. The tetragonal phase arises from the collective Jahn–Teller distortion along one of the axes of the octahedral sites, which is typical for Cu2+ ions (d9) as a consequence of the removal of the eg orbital degeneracy [10,11] For this reason, many studies have been focused on synthesizing copper ferrite nanoparticles with a wide number of methods including thermal decomposition [12], hydrothermal [13], solvothermal [14], co-precipitation [15], electrospinning [16] and solgel [17], taking into account that the desired crystalline phase might be obtained by selecting an appropriate thermal treatment. This affects the magnetic properties and makes it difficult to achieve a precise control over the different parameters at play in giving rise to the final magnetic behavior [19]

Methods

Results

Conclusion