Structural properties of ultrafine Ba-hexaferrite nanoparticles

Crystal structure of ultrafine Ba-hexaferrite (BaFe12O19) nanoparticles was studied using X-ray diffractometry (XRD), high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDXS), X-ray absorption fine structure (XAFS), and Mössbauer spectroscopy (MS), to be compared to the structure of larger nanoparticles and the bulk. The nanoparticles were synthesized with hydrothermal treatment of an appropriate suspension of Ba and Fe hydroxides in the presence of a large excess of OH−. The ultrafine nanoparticles were formed in a discoid shape, ∼10 nm wide and only ∼3 nm thick, comparable to the size of the hexagonal unit cell in the c-direction. The HRTEM image analysis confirmed the hexaferrite structure, whereas EDXS showed the composition matching the BaFe12O19 formula. XAFS and MS analyses showed considerable disorder of the structure, most probably responsible for the low magnetization.