Nanomanufacturing: Conversion of antiferromagnetic hematite (α-Fe2O3) nanocubes to ferrimagnetic spherical barium ferrite (BaFe12O19) nanoparticles

Recently, it has been shown that it is feasible to realize 29.5 Gb/in recording density employing hexagonal barium ferrite (H-BaFe) nanoplatelets [1]. Although H-BaFe nanoplatelets are a potential candidate for high density recording media, their greatest disadvantage is their dispersibility and agglomeration by forming poker-chip-like stacks due to mutual magnetic interactions [2-3]. To achieve better media recording performance, use of nano-sized spherical barium ferrite (S-BaFe) particles has been previously proposed. Hence, we have developed 24 30 nm sized S-BaFe particles [4]. However, the particle size is still too large. In this paper, we report 20 25 nm sized S-BaFe particles having extremely narrow size distribution and no superparamagnetic phase. We have converted hematite nanoocubes to S-BaFe nanoparticles using an adsorption-diffusion process [4]. Fig. 1 (a, b) shows the TEM micrograph of the 21 nm hematite nanocubes and the converted 20 25 nm sized S-BaFe particles. Mössbauer spectra shown in Fig. 1 (c) clearly demonstrate that the converted particles are S-BaFe, and there is no superparamagntic phase owing to extremely narrow particle size distribution. The saturation magnetization and the coercivity of the S-BaFe particles were observed to be 45.4 emu/g and 3015 Oe, respectively.