Magnetic Behavior of Magnetite and Cobalt Ferrite Particles in Magnetic Fluid and their Local Structure Analysis Using EXAFS (磁性流体--材料と応用<特集>)

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The particles in magnetic fluid relaxes in the field direction through either Neel or Brownian relaxation. The relaxation mechanism is very much influenced by the anisotropy constant of the particle. In this paper, the relaxation mechanism under various states and conditions for magnetite and cobalt ferrite magnetic fluid in the temperature range of 83-293K is discussed by measuring the initial susceptibility of the system. Our results suggest that the magnetite magnetic fluid contains a mixture of non-superparamagnetic and superparamagnetic particles, whereas, the cobalt ferrite magnetic fluid contains exclusively of nonsuperparamagnetic particles. The results of local structure analysis on coprecipitated magnetite was comparable to that of Kamaishi magnetite except the distance between Fe and 0 atoms which was shorter. This suggests the possible vacancies in the octahedral sites in co-precipitated magnetite. In the case of coprecipitated cobalt ferrite, the Co and Fe atoms are well dispersed in the structure. The distance of the second nearest neighbor peak at Fe K-edge shows a decrease and at the same time at Co K-edge shows an increase meaning a slight difference in the cation distribution compared to cobalt ferrite produced by ceramic method.
社団法人粉体粉末冶金協会の論文