Figure 1

Transmission electron microscopy images of $\alpha \text{−}{\mathrm{Fe}}_2{\mathrm{O}}_3$ nanoparticles. (a), (b) HREM images showing that the particles are attached to one another along their common [001] axis. The arrows and angles indicate the direction of the [001] axis of the particles relative to the plane of the paper. The arrows point into the paper. (c) Cryo-TEM image of a frozen aqueous suspension of the particles. (d) Electron micrograph of the separated $\alpha \text{−}{\mathrm{Fe}}_2{\mathrm{O}}_3$ particles (dark spots) after grinding with amorphous $\mathrm{Si}{\mathrm{O}}_2$ particles (the gray matrix of the composite).Reuse & Permissions

Figure 2

(Color online) Diffraction data (background subtracted) of $\alpha \text{−}{\mathrm{Fe}}_2{\mathrm{O}}_3$ particles obtained at room temperature. (a) HES-XRD data of the as-prepared nanoparticles. (b) NPD data of the same sample as in (a). (c) NPD data of the $\alpha \text{−}{\mathrm{Fe}}_2{\mathrm{O}}_3$ sample after grinding. In (b) and (c), the solid lines represent the fits with Gaussian shaped peak profiles to the data (green denotes individual peaks, red the sum of peaks). (d) Schematic illustration of the antiferromagnetic correlation across the particle interfaces in the as-prepared sample. (e) Correlation lengths obtained for the as-prepared sample from HES-XRD (open dots) and NPD (filled dots) data by Fullprof fitting (first quadrant), and by fitting with pseudo-Voigt (third quadrant) and Gaussian (fourth quadrant, gray) peak profiles. Stars denote magnetic reflections. (f) Correlation lengths from Fullprof fitting for the ground sample, based on NPD data. The ellipses in (e) and (f) are guides to the eye obtained from the Fullprof fit.Reuse & Permissions

Figure 3

Mössbauer spectra of $\alpha \text{−}{\mathrm{Fe}}_2{\mathrm{O}}_3$ nanoparticles. (a) The as-prepared sample measured at ambient temperature. (b) The ground sample at ambient temperature. (c) The ground sample at $80\mathrm{K}$.Reuse & Permissions

Figure 4

Illustration of network of interacting $\alpha \text{−}{\mathrm{Fe}}_2{\mathrm{O}}_3$ nanoparticles showing suppressed superparamagnetic relaxation at room temperature.Reuse & Permissions