高保磁力ナノ粒子の化学合成 : 酸化物および金属ナノ粒子について

概要

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First, the synthesis of cobalt ferrite particles by using the growth assisted (a) co-precipitation and (b) oxidation methods is described. In the coprecipitation method, the room temperature (RT) coercivity (H_c) was enhanced to 2.9 kOe for the seeded cobalt ferrite nanoparticles in contrast to the H_c of 1.31 kOe for the seed. On the other hand, in the case of oxidation method, particles ranging from 15 to 110 nm were synthesized by controlling the ratio of Fe^<3+>/(Fe^<3+>+Fe<2+>). The highest H_c of 2.02 kOe was recorded for particles with average diameter around 35 nm. Rotational hysteresis loss (W_r) analysis carried out particles synthesized by both methods suggested that the critical single domain size is about 40 nm with RT H_c as high as 4.65 kOe. Then, the synthesis of FePt particles with different crystal structures by using the 'polyol process' is described. Both superparamagnetic and ferromagnetic FePt particles were synthesized by regulating the reaction kinetics. FePt nanoparticles with diameters below 10 nm and fct in structure were obtained in the assynthesized state. Mdssbauer results show magnetic ordering at room temperature itself along with a superparamagnetic doublet. The degree of ordering was estimated to be around 60%. The magnetization and coercivity of these particles were 51 emu/g and about 2.1 kOe.
社団法人日本磁気学会の論文
2004-08-01