Spark-plasma-sintering magnetic field assisted compaction of Co_(80)Ni_(20) nanowires for anisotropic ferromagnetic bulk materials

摘要

We developed a two-step process showing the way for sintering anisotropic nanostructured bulk ferromagnetic materials. A new reactor has been optimized allowing the synthesis of several grams per batch of nanopowders via a polyol soft chemistry route. The feasibility of the scale-up has been successfully demonstrated for Co_(80)Ni_(20) nanowires and a massic yield of ~97% was obtained. The thus obtained nanowires show an average diameter of ~6nm and a length of ~270nm. A new bottom-up strategy allowed us to compact the powder into a bulk nanostructured system. We used a spark-plasma-sintering technique under uniaxial compression and low temperature assisted by a permanent magnetic field of 1 T. A macroscopic pellet of partially aligned nanowire arrays has been easily obtained. This showed optimized coercive properties along the direction of the magnetic field applied during compaction (i.e., the nanowires' direction).