Preparation of monodispersed magnetic Particles and its magnetic Properties

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(1)Preparation of monodispersed maghemite particles and its propertiesWell defined monodispersed maghemite particles were produced by transforming monodispersed spindle-like hematite particles and magnetic properties of the solids were examined. The coercive force of the particles showed maximum at a length the long axis of 4 mum with the axial ratio of 3- 4.5. The coercive force of the magnetic particles obtained from hematite particles of which axial ratio was controlled by desolving the solids in hydrochloric acid proportionally decreased with the decrease in the axial ratio. The rod-like magnetic particles prepared in alkaline conditions showed lower coercive force than that of spindle-like ones prepared in acidic conditions.(2) When magnetic fields were applied to the hematite dispersion of spindle-like particles, changes in the sedimentation potential were found. It was found that the changes with increase in magnetic fields could be well expressed by the Langevin function. It was concluded that the changes in the sedimentation potential with the magnetic field was brought about by the increase in the friction of the particles with solvent due to the orientation of the spindle-like particles.(3) Loop-like agglomeration of the spindle-like particles was found and the mechanism of the loop formation was investigated. The loop formation was could be explained by DLVO theory taking into account of the magnetic interactions.