Magnetic hysteresis, Fe-57 Mossbauer and X-ray data are presented for spherical 250 nm particles of solid solutions in the spinel system Fe3O4-gamma-Fe2O3 (Fe3-u square O-u(4), 0 <= 1/3 (square =cation vacancy)). For dispersed particles, the composition of u similar to 0.24 exhibits maxima of coercive force H-c similar to 25kA/m, relative saturation remanence sigma(rs)/sigma(s)similar to 0.3, switching field distribution H-SFD similar to 100 kA/m and of anhysteretic remanence susceptibility at room temperature. The experimental results point to single domain particles with non-homogeneous magnetization mode or to a magnetization mode intermediate between single domain and two domain particles. The maxima are probably a consequence of the superposed action of (i) Fe2+-single ion anisotropy and (ii) microstresses. Mossbauer spectra were used to analyse the cation distribution on A- and B-sites of the spinel lattice. The experimental data were found to disagree with the cation distribution according to a formula used in the literature for Mossbauer analysis. From X-ray diffractograms, lattice parameters a(0) and intensity of superstructure reflections, due to ordering of square in the spinel lattice, were determined as a function of the 0 concentration it. The reflections are in agreement with a tetragonal cell with c(0)/a(0) = 3 which has been frequently observed for gamma-Fe2O3 (u = 1/3) in the literature. (C) 2005 Elsevier B.V. All rights reserved.
