Enhanced Coercivity In Co-Doped Alpha-Fe2o3 Cubic Nanocrystal Assemblies Prepared Via A Magnetic Field-Assisted Hydrothermal Synthesis

Ferromagnetic Co-doped alpha-Fe2O3 cubic shaped nanocrystal assemblies (NAs) with a high coercivity of 5.5 kOe have been synthesized via a magnetic field (2 kOe) assisted hydrothermal process. The X-ray diffraction pattern and Raman spectra of alpha-Fe2O3 and Co-doped alpha-Fe2O3 NAs confirms the formation of single-phase alpha-Fe2O3 with a rhombohedral crystal structure. Electron microscopy analysis depict that the Co-doped alpha-Fe2O3 NAs synthesized under the influence of the magnetic field are consist of aggregated nanocrystals (similar to 30nm) and of average assembly size 2 mu m. In contrast to the NAs synthesized with no magnetic field, the average NAs size and coercivity of the Co-doped alpha-Fe2O3 NAs prepared with magnetic field is increased by 1 mu m and 1.4 kOe, respectively. The enhanced coercivity could be related to the well-known spin-orbit coupling strength of Co2+ cations and the redistribution of the cations. The size increment indicates that the small ferromagnetic nanocrystals assemble into cubic NAs with increased size in the magnetic field that also lead to the enhanced coercivity. (C) 2017 Author(s).