High speed processing of NiFe2O4 spinel using a laser furnace

The Laser Furnace (LF) method has been applied to directionally solidify NiFe2O4 spinel disks from a mixture of Fe and Ni oxides in order to obtain uniform, dense targets for controlled synthesis of spinel nanoparticles via Laser Ablation. Application of a CO2 laser in Line Scan mode onto a sample with the desired stoichiometry, enabled melt processing above 1580 °C at its outer surface layer. This process was carried out inside a continuous roller furnace at a maximum volume temperature of 1000 °C. Such combination helps avoid excessive thermal stress, crack formation and catastrophic failure of these magnetic ceramic monoliths. Higher energy incubation values yield increased molten volumes and a thicker resolidified surface layer with a dense microstructure. Despite the high solidification rates imposed, NiFe2O4 spinel is the main phase obtained according to X-Ray Diffraction (XRD) and magnetization studies. LF processed samples exhibit a reduction of the coercive fields and an increase of the saturation magnetization values, evidence for soft ferromagnetism and characteristic of the magnetic behaviour associated with this spinel. This work demonstrates the convenience of the LF method for preparation of uniform, dense targets for Laser Ablation and other evaporation based techniques used in the fabrication of nanoparticles.