Distribution of cations in nanosize and bulk Co-Zn ferrites

The structural and magnetic properties of Co(1-x)Zn(x)Fe(2)O(4) ferrites (Co-Zn ferrites) are investigated in a narrow compositional range around x = 0.6, which is of interest because of applications in magnetic fluid hyperthermia. The study by x-ray and neutron diffraction, Mossbauer spectroscopy and magnetization measurements is done on nanoparticles prepared by the coprecipitation method and bulk samples sintered at high temperatures. In spite of the known preference of Zn(2+) for tetrahedral (A) sites and Co(2+) for octahedral [B] sites, the cations are distributed nearly evenly over the two sites of spinel structure and there is also a variable number of [B] site vacancies (square), making cobalt ions trivalent. In particular for x = 0.6, the cationic distribution is refined to (Co(0.22)(3+)Zn(0.31)(2+)Fe(0.48)(3+))[Co(0.16)(3+)Zn(0.26)(2+)Fe(1.43)(3+)square(0.14)]O(4) and (Co(0.15)(2+)Zn(0.46)(2+)Fe(0.39)(3+))[Co(0.08)(2+)Co(0.16)(3+)Zn(0.13)(2+)Fe(1.57)(3+)square(0.06)]O(4) for the 13 nm particles (T(C) = 335 K) and bulk sample (T(C) = 351 K), respectively.