Tuning the particle size, natural ferromagnetic resonance frequency and magnetic properties of -FeO nanoparticles 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 ( -Fe 2 O 3 ) 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 -Fe 2 O 3 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 -Fe 2 O 3 particles. It was also demonstrated that the duration of -Fe 2 O 3 synthesis can be considerably reduced by increasing the rate of tetraethoxysilane hydrolysis, while the magnetic properties of the target material do not degrade. A fast method for the synthesis of -Fe 2 O 3 , yielding 100% pure material with a variable FMR frequency, is proposed.