Facile batch-scale production of spinel ferrite for permanent magnet application

The rising demand for rare-earth elements to realize permanent magnets for renewable energy pro-duction and other industrial applications is pushing the search of new rare-earth free solutions [1]. In this contribution, we propose a facile batch-scale production of nanostructured cobalt ferrite (CoFe2O4 - CFO) to sustain the large-scale production of novel rare- earth free permanent mag-nets. The proposed production is based on the design of tailored milling process of CFO powders produced by solid state reaction [2]. Two different calcination temperatures (1120 K and 1320 K) fol-lowed by milling in two steps, reducing the milling media size, were chosen. CFO nanoparticles with crystallite size of 33 nm, after the first milling step and mean particle size of 9 nm after the second milling step was achieved. The results from the magnetic characterization, performed by evaluating both the dynamic and static properties, show how the milling process affect the microstructure, and what the strengths and issues of the process are. The obtained energy product, (BH)max, which is the figure of merit for permanent magnets was found for randomly oriented powders over 2 MGOe. In principle, this value can be significantly further increased by orienting the nanograins under the application of an external magnetic field. This result makes this material extremely appealing as a building block to design novel permanent magnets alternative to RE-based ones, at least in the intermediate region of the energy product map, where the latter are currently employed simply because standard ferrites do not have large enough energy product.