The purpose of this study is to synthesis cobalt ferrite nanoparticles in the presence of external magnetic field and investigation of the structural and magnetic properties of the nanoparticles. The first series of the samples were annealed for 1.5 h at 400 o C in the magnetic fields of 0 , 4 and 8 kOe. Rietveld analysis of the X-ray diffraction patterns indicated that, increasing the external magnetic field decreases the lattice parameter of the spinel structure. According to the FE-SEM images, by applied magnetic field, the morphology of the samples is not dramatically change. Moauer spectrum show that, external magnetic field leads to the change in the cations distribution in the spinel sites. In the second series, the samples were annealed for 3 h at 400 o C in different magnetic fields of 0, 4, 6, 8 kOe. From XRD analysis, it was found that the lattice constant changes with the change of the applied magnetic field. According to the SEM images, morphology of the sample prepared at 8 kOe is changed, relative to the samples prepared at lower magnetic fields. By SQUID magnetometer, it was found that the saturation magnetization changes by changing the external magnetic field. From Moauer spectrum, it was concluded that the changing of saturation magnetization is mainly related to the change of the cations distribution in the spinel structure. In the second part of project, nano-chains of nickel ferrite (NiFe 2 O 4 ) with PEG polymer was prepared in the presence of external magnetic field. FE-SEM images confirmed that, the applied magnetic field changes the size of particles in the chains.
