Electrochemical Synthesis of New Magnetic Mixed Oxides of Sr and Fe:  Composition, Magnetic Properties, and Microstructure

An electrochemical method for the preparation of magnetic nanoparticles of new Sr−Fe oxides is presented in this work. It consists of the electrolysis of nitrate or chloride solutions with Sr 2+ and Fe 3+ salts using commercial Fe electrodes. Magnetic materials are collected as precipitates from nitrate media in the pH range 1−3 and from chloride media within the pH range 1−12. The presence of 100−300 ppm aniline in acidic nitrate media yields a decrease in energy cost and particle size. Inductively coupled plasma analysis of materials and energy-dispersive X-ray spectrometry of single particles confirm that they are composed of mixed oxides of Sr and Fe. All synthesized materials crystallize as inverse cubic spinels, usually with intermediate structures between magnetite and maghemite. They are formed by nanoparticles with average sizes from 2 nm to ∼50 nm, as observed by scanning electron microscopy. The electrogenerated mixed oxides have higher saturation magnetization, but lower remanent magnetization and coercive field, than commercial strontium hexaferrite with micrometric particle size.