Concentration of immobilized $\varepsilon$-iron oxide nanoparticles as a basis for obtaining highly filled magnetically hard materials

The results of the study of the magnetic properties of the powder system of iron oxide nanoparticles $\varepsilon$-Fe$_2$O$_3$ (average size of 10 nm) are reported. The nanoparticles were obtained from a previously prepared composite material $\varepsilon$-Fe$_2$O$_3$/SiO$_2$ xerogel containing 20 wt.% $\varepsilon$-Fe$_2$O$_3$ by dissolving the SiO$_2$ matrix. The results of X-ray diffraction and Mössbauer spectroscopy confirmed the structure of $\varepsilon$-Fe$_2$O$_3$. From the analysis of magnetic measurements and the results of Mossbauer spectroscopy, it is possible to state the presence of a magnetic transition known for $\varepsilon$-Fe$_2$O$_3$ in the range of 75–150 K. This indicates the preservation of the magnetic characteristics of the particles after the matrix removal procedure and opens the possibility of obtaining a highly filled magnetically hard material based on $\varepsilon$-iron oxide.