Tuning the particle size, natural ferromagnetic resonance frequency and magnetic properties of ϵ-Fe2O3nanoparticles prepared by a rapid sol-gel method

In this study, we demonstrate the synthesis and the investigation of magnetostatic and magnetodynamic properties of epsilon iron oxide (ε-Fe2O3) nanoparticles of various sizes. Silica gels were obtained by rapid hydrolysis of tetraethoxysilane in an aqueous–alcoholic solution of iron(III) nitrate and then dried to form xerogels. The annealing of the xerogels at temperatures of 1000–1250 °C led to the formation of ε-Fe2O3 particles with average sizes of 7–38 nm, respectively. With an increase in the annealing temperature, the coercivity of the samples increased and reached 21 kOe for 1200 °C, while the frequency of the natural ferromagnetic resonance increased from 161 to 170 GHz followed by narrowing of the absorption lines from 40 to 2 GHz. It was shown for the first time that the parameters of the natural ferromagnetic resonance line of epsilon iron oxide can be varied by controlling the size of ε-Fe2O3 particles. It was also demonstrated that the duration of ε-Fe2O3 synthesis can be considerably reduced by increasing the rate of tetraethoxysilane hydrolysis, while the magnetic properties of the target material do not degrade.