Ensemble magnetization of magnetic nanoparticles (NPs) has a sensitive dependence on the structural arrangement of particles. To better understand the correlation between spatial positions of NPs and ensemble magnetization, an experimental system is needed where particle position can be adjusted while simultaneously probing nanoscale magnetization. Here, we describe experiments using polarization analyzed small angle neutron scattering (PASANS) to study the change in magnetic correlations of ~7 nm iron oxide (Fe<sub>3</sub>O<sub>4</sub>) NPs embedded in stretched silicone rubber. PASANS is a powerful tool for mapping both the inter- and intra- particle magnetization of NPs on length scales ranging from 0.1 – 100 nm. The magnetic NP polymer gel, or magnetogel, can be stretched on the neutron beamline during an experiment. The macroscopic stretching is accompanied by nanoscale deformations, where polymer chains move to accommodate a new equilibrium configuration. NPs embedded in the gel change their configuration as a function of applied stress, providing a method to adjust the average center-to-center spacing between particles. The scattering data from the unstretched gel in a 1 T applied magnetic field can be modelled by 7.4 nm iron oxide NPs assembled in a hard sphere packing with 30% volume fraction. When the sample is stretched 3x its original size in a direction parallel to the applied field, the morphology changes dramatically. Specifically, the data can be described using a cluster model where NP dimers have emerged (Figures 1a and 1b). Stretching causes the particles to morph from semi-close packed, but individual, 7.4 nm diameter NPs into dimer-like clusters that are 15 nm long, as viewed perpendicular to the applied field (Figures 2a and 2b). These PASANS experiments clearly demonstrate that stretching the magnetogel modulates the structural characteristics of magnetic NPs in a pronounced, controllable manner.

![](https://assets.underline.io/uploads/markdown_image/1/image/39e948b29d4a9faea0cd8a27867ee2bb.jpg)

Fig. 1: Magnetic scattering from (a) unstretched and (b) 3x stretched gel in a 1 T field. The data set in (a) is fit to a hard sphere-like packing and (b) is fit to a model containing dimers

![](https://assets.underline.io/uploads/markdown_image/1/image/5b350fa63e4727cecd3c135d0fb252f5.jpg)

Fig. 2: Schematic showing rearrangement of NPs in (a) unstretched and (b) 3x stretched configurations.




Magnetic Correlations of Iron Oxide Nanoparticles as Probed by PASANS in Stretched Magnetogel Composites

**Session chair:** Victor Prida, University of Oviedo



EOC - Magnetic Nanostructures

technical paper

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This Conference provides an outstanding opportunity for worldwide participants to meet their colleagues and collaborators and discuss developments in all areas of magnetism research.

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Magnetic Correlations of Iron Oxide Nanoparticles as Probed by PASANS in Stretched Magnetogel Composites

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