Magnetic hysteresis properties, Mössbauer spectra and structural data of spherical 250 nm particles of solid solutions Fe3O4Fe3O4–γγ-Fe2O3Fe2O3

Magnetic hysteresis, 57Fe Mössbauer and X-ray data are presented for spherical 250 nm particles of solid solutions in the spinel system Fe3O4Fe3O4–γγ-Fe2O3Fe2O3 (Fe3-u□uO4Fe3-u□uO4, 0⩽u⩽1/30⩽u⩽1/3 (□=cation□=cation vacancy)). For dispersed particles, the composition of u∼0.24u∼0.24 exhibits maxima of coercive force Hc∼25kA/m, relative saturation remanence σrs/σs∼0.3σrs/σs∼0.3, switching field distribution HSFD∼100kA/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+Fe2+—single ion anisotropy and (ii) microstresses. Mössbauer 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 Mössbauer analysis. From X-ray diffractograms, lattice parameters a0a0 and intensity of superstructure reflections, due to ordering of □□ in the spinel lattice, were determined as a function of the □□ concentration uu. The reflections are in agreement with a tetragonal cell with c0/a0=3c0/a0=3 which has been frequently observed for γγ-Fe2O3Fe2O3 (u=13) in the literature.