Nanosized powders of NiZn ferrite: Synthesis, structure, and magnetism

The structure and magnetic behavior of nanostructured powders of stoichiome tric NiZn ferrite, Ni0.5Zn0.5Fe2O4, synthesized by coprecipitation, are inv estigated by extended x-ray-absorption fine structure spectroscopy (EXAFS), x-ray diffraction, Mossbauer spectroscopy, and vibrating sample magnetomet ry. Samples of high purity and high homogeneity were obtained by annealing at relatively low temperatures (300-800 degrees C) resulting in nanoparticl es with average diameter between 9 and 90 nm, as determined by x-ray diffra ction. EXAFS was applied to follow Ni, Zn, and Fe cations distribution and the evolution of the short range order of the samples with increasing annea ling temperature. Our results show ferrimagnetic NiZn ferrite nanosized pow ders with high purity, 1:1 Ni to Zn stoichiometric ratio and superparamagne tic behavior. Moreover, the samples exhibit good structural ordering alread y after heat treatment at 400 degrees C. Analysis by vibrating sample magne tometry indicated a critical particle diameter for the transition from mono domain to multidomain behavior close to 40 nm. (C) 2000 American Institute of Physics. [S0021-8979(00)08309-2].