Study on preparation of ultrafine NiFe₂O₄ particles by microemulsion method

Ultrafine NiFe₂O₄ particles with spinel structure were prepared in the system of water-in-oil microemulsion of water/Triton X-100/n-hexanol/cyclohexane. The effects of calcining temperature and the other operation conditions were systematically discussed based on the techniques of SEM, XRD, VSM and so on. The result showed that NiFe₂O₄ nanoparticles, with a narrow size distribution(30-70nm), could be obtained by microemulsion method. The crystal grain diameter of the ultrafine NiFe ₂O₄ particles could be enhanced with the improvement of the calcining temperature, the molar ratio of water to surfactant (w=[H ₂O]/ [surfactant]) and the concentration of Fe³⁺(or Ni²⁺), respectively. The VSM plots showed that the ferrimagnetic behavior was expected for this type of magnetic material. The XRD patterns and DTA-TG curves revealed that the optimal calcining temperature of NiFe ₂O₄ sample was at around 500°C. The relation between the average particle size (D) and the value of w could be expressed as D=13.911+0.2628w. Moreover, it was indicated that low concentration of Fe ³⁺(or Ni²⁺) was beneficial to the formation of small and regular NiFe₂O₄ particles.