Abstract
Iron oxide nanoparticles find a wide variety of applications, including targeted drug delivery and hyperthermia in advanced cancer treatment methods. An important property of these particles is their maximum net magnetization, which has been repeatedly reported to be drastically lower than the bulk reference value. Previous studies have shown that planar lattice defects known as antiphase boundaries (APBs) have an important influence on the particle magnetization. The influence of APBs on the atomic spin structure of nanoparticles with the γ-Fe2O3 composition is examined via Monte Carlo simulations, explicitly considering dipole-dipole interactions between the magnetic moments that have previously only been approximated. For a single APB passing through the particle centre, a reduction in the magnetization of 3.9% (for 9 nm particles) to 7.9% (for 5 nm particles) is found in saturation fields of 1.5 T compared with a particle without this defect. Additionally, on the basis of Debye scattering equation simulations, the influence of APBs on X-ray powder diffraction patterns is shown. The Fourier transform of the APB peak profile is developed to be used in a whole powder pattern modelling approach to determine the presence of APBs and quantify them by fits to powder diffraction patterns. This is demonstrated on experimental data, where it could be shown that the number of APBs is related to the observed reduction in magnetization.
Highlights
The increasing number of existing and potential applications for superparamagnetic iron oxide nanoparticles (SPIONs) has sparked considerable interest from both a technological and a scientific point of view
SPIONs are used in the field of medicine for tissue repair (Bock et al, 2010; Pareta et al, 2008; Tran & Webster, 2009) and targeted drug delivery (Dobson, 2006; Veiseh et al, 2010; Sun et al, 2008), as contrast agents for magnetic imaging (Josephson et al, 1999; Semelka & Helmberger, 2001; Corot et al, 2006; Jun et al, 2008; Laurent et al, 2008; Sun et al, 2008; Ma et al, 2015) and magnetic particle imaging (Gleich & Weizenecker, 2005), and in cancer treatment by magnetic hyperthermia (Johannsen et al, 2005; Hergt et al, 2006; Gonzales-Weimuller et al, 2009; Krishnan, 2010; Kumar & Mohammad, 2011; Laurent et al, 2011; Deatsch & Evans, 2014)
The origin of this reduction appears to be a combination of several effects, such as spin canting near defects (Disch et al, 2012; Herlitschke et al, 2016), surface spin canting and the presence of antiphase boundaries (APBs) (Nedelkoski et al, 2017; Kohler et al, 2021)
Summary
The increasing number of existing and potential applications for superparamagnetic iron oxide nanoparticles (SPIONs) has sparked considerable interest from both a technological and a scientific point of view. The origin of this reduction appears to be a combination of several effects, such as spin canting near defects (Disch et al, 2012; Herlitschke et al, 2016), surface spin canting and the presence of antiphase boundaries (APBs) (Nedelkoski et al, 2017; Kohler et al, 2021). The last have a strong influence on the magnetic properties of iron oxide nanoparticles (Kohler et al, 2021) and are the subject of this study
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