Spatially Resolved Disorder Anisotropies in Ferrite Nanoparticles
arxiv(2019)
摘要
The technological performance of magnetic nanoparticles is dominated by finite size and disorder effects. However, it is often difficult to isolate intrinsic effects such as magnetic disorder at the particle surface. Despite numerous efforts and advanced techniques, the three-dimensional magnetism of spin disorder and its nanoscale distribution within magnetic nanoparticles remains a key challenge. Here we present the spatially resolved, non-correlated surface spin disorder in isolated, spherical cobalt ferrite nanoparticles, derived by a combination of polarized small-angle neutron scattering and micromagnetic analysis. The field-dependence of the coherently magnetized particle volume, which is not accessible with conventional integral measurement techniques, illustrates how the nanoparticle magnetization overcomes structural surface disorder. Our results allow to estimate the magnetic disorder energy, which is required to polarize gradually the surface spins, with spatial resolution within the nanoparticles. Such unprecedented knowledge of the intraparticle spin disorder and associated anisotropies will be decisive for a rational nanomaterials development.
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