Platelets of strontium hexaferrite (SrFe 12 O 19 , SFO), up to several micrometers in width, and tens of nanometers thick have been synthesized by a hydrothermal method. They have been studied by a combination of structural and magnetic techniques, with emphasis on Mössbauer spectroscopy and X-ray absorption based-measurements including spectroscopy and microscopy on the iron-L edges and the oxygen-K edge, allowing us to establish the differences and similarities between our synthesized nanostructures and commercial powders. The Mössbauer spectra reveal a greater contribution of iron tetrahedral sites in platelets in comparison to pure bulk material. For reference, high-resolution absorption and dichroic spectra have also been measured both from the platelets and from pure bulk material. The O-K edge has been reproduced by density functional theory calculations. Out-of-plane domains were observed with 180° domain walls less than 20 nm width, in good agreement with micromagnetic simulations.

The magnetic properties of $${\text{SrFe}}_{12}{\text{O}}_{19}$$ SrFe 12 O 19 , a paradigmatic hexaferrite for permanent magnet applications, have been addressed in detail combining density functional theory including spin–orbit coupling and a Hubbard U term with Monte Carlo simulations. This multiscale approach allows to estimate the Néel temperature of the material from ab initio exchange constants, and to determine the influence of different computational conditions on the magnetic properties by direct comparison versus available experimental data. It is found that the dominant influence arises from the choice of the Hubbard U term, with a value in the 2–3 eV range as the most adequate to quantitatively reproduce the two most relevant magnetic properties of this material, namely: its large perpendicular magnetocrystalline anisotropy and its elevated Néel temperature.

We address the detailed description of the magnetic properties of the (001) and (111) interfaces between the hard CoFe2O4 (CFO) and soft NiFe2O4 spinel ferrites, used in bicomponent systems for permanent magnet applications. The similarity between the electronic properties, magnetic order and lattice structure of both oxides allows us to isolate the effect of ideal interface formation on the magnetism of the combined system based on density functional theory. While the magnetic moments and long-range magnetic order preserve bulk-like values, the magnetic anisotropy is reduced by the presence of the interface, and depends on the specific termination. Partial inversion of CFO is also relevant, as it enhances the net magnetization and alters both the magnitude and spatial dependence of the magnetic anisotropy.

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