Bottom-up and new compaction processes: A way to tunable properties of nanostructured cobalt ferrite ceramics

► A novel bottom-up strategy combing soft chemistry and Spark plasma sintering was employed to process bulk nanostructured spinel CoFe2O4 with limited particle growth ► Bulk nanostructured spinel CoFe2O4 show superparamagnetic behavior with a blocking temperature significantly higher than room temperature ► Hardness of bulk nanostructured spinel can be varied from that of metal to that of hard ceramic In this work we describe a novel bottom-up strategy to process cobalt ferrite CoFe 2O 4 nanostructured bulk material. This strategy offers the possibility to drive their magnetic and mechanical properties in a wide range of different behaviors. In particular, we show how to tune the blocking temperature along with optimized mechanical strength. This method combines forced hydrolysis in polyol, a soft chemistry route, and Spark Plasma Sintering (SPS) for consolidation. To highlight this method, we also performed compaction by a standard Hot Isostatic Pressing (HIP) process. Thus we compare the nanostructured bulk microstructures (for both compaction techniques) and magnetic static properties to those of several CoFe 2O 4 nanopowder samples showing particle size and annealing temperatures comparable to those of the nanostructured bulk samples. Microstructure, radio-crystallographic and magnetic studies have been carried out in order to show the optimization of the processing strategy in this work.