CTAB-assisted low-temperature synthesis of SrFe12O19 ultrathin hexagonal platelets and its formation mechanism

Single domain particles (50-150 nm) of the M-type strontium ferrite (SrFe12O19) were synthesized via co-precipitation method using cetyltrimethyl ammonium bromide (CTAB) as a surfactant, followed by heat treatment at 900 degrees C for 2 h. The effects of CTAB contents (x=0,1,3, 6, 9 wt.%) on formation, structure, morphology and magnetic properties of the strontium hexaferrite particles were investigated. Single phase M-type ferrite powders with ultrathin hexagonal platelet-like (thickness: 10-20 nm) morphology were obtained in the existence of CTAB surfactant, whereas secondary phase alpha-Fe2O3 was detected in the samples prepared without CTAB, exhibiting rod-like shape. Both the saturation magnetization and coercivity increased with CTAB content up to x=6 wt.% and the optimal values were 68.7 emu/g and 6620 Oe, respectively. These results implied that CTAB may act as a crystallization master, controlling the nucleation and growth of the crystals. Two distinct formation mechanisms have been proposed to explain the different SrFe12O19 particle morphologies. These nanoparticles are promising for the building blocks of hard magnets and magnetic recordings. (C) 2012 Elsevier B.V. All rights reserved.