SAIP2026

The Synthesis and Characterization of ε-Fe$_{2}$O$_{3}$/SiO$_{2}$ Nanoparticles

9 Jul 2026, 12:20

20m

Lecture Hall GH1 (University of the Western Cape)

Oral Presentation Track A - Physics of Condensed Matter and Materials Physics of Condensed Matter and Materials

Speaker

Aphile Chithwayo (Student)

Description

This study investigates the temperature-dependent magnetic properties and structural transitions of ε-Fe$_{2}$O$_{3}$ nanoparticles embedded in a silica matrix, synthesized via the sol-gel method. While literature reports an exceptionally large room-temperature coercivity of ε-Fe$_{2}$O$_{3}$ approximately = 2 T (20 kOe), often attributed to its disordered structure, the precise effects of structural deformations on its magnetic transitions and magnetocrystalline anisotropy remain a subject of active research. The coercivity is also reported to show an unusual temperature trend, decreasing with temperature until around 100 K and then increasing until 2 K. In this study, the X-ray diffraction (XRD) confirmed the successful synthesis of the ε-Fe$_{2}$O$_{3}$ phase with an α-Fe$_{2}$O$_{3}$ component, while Transmission Electron Microscopy (TEM) revealed mor-phologies ranging from elliptical to nearly spherical. Further investigation was done using the HRTEM where images revealed distinct lattice fringes, indicative of the well-ordered crystal-line structure of the nanoparticles.
Room-temperature 57Fe Mössbauer spectroscopy confirmed a magnetically ordered state, with spectral fitting requiring four sextets: one representing α-Fe$_{2}$O$_{3}$ and three corresponding to the distinct Fe$^{3+}$ coordination sites within the ε-Fe$_{2}$O$_{3}$ lattice. Magnetic hysteresis (M-H) loops recorded between 10 K and 300 K revealed a rich thermal behavior; at 300 K, the nanoparti-cles exhibited a high coercivity of H$_{c}$ = 1.55 T (15.5 kOe) and a remanent magnetization of M$_{r}$ = 0.27 emu/g. Notably, a pronounced collapse in both coercivity and magnetic squareness was observed upon cooling, particularly near 100 K, which is attributed to an incommensurate magnetic transition. These results highlight critical limitations for the application of ε-Fe$_{2}$O$_{3}$ as a hard magnetic material at cryogenic temperatures.