Magnetic hysteresis properties, Mössbauer spectra and structural data of spherical 250 nm particles of solid solutions [formula omitted]– [formula omitted]- [formula omitted

Abstract

Magnetic hysteresis, 57Fe Mössbauer and X-ray data are presented for spherical 250 nm particles of solid solutions in the spinel system Fe 3 O 4 – γ - Fe 2 O 3 ( Fe 3 - u □ u O 4 , 0 ⩽ u ⩽ 1 / 3 ( □ = cation vacancy)). For dispersed particles, the composition of u ∼ 0.24 exhibits maxima of coercive force H c ∼ 25 kA / m , relative saturation remanence σ rs / σ s ∼ 0.3 , switching field distribution H SFD ∼ 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) Fe 2 + —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 a 0 and intensity of superstructure reflections, due to ordering of □ in the spinel lattice, were determined as a function of the □ concentration u . The reflections are in agreement with a tetragonal cell with c 0 / a 0 = 3 which has been frequently observed for γ - Fe 2 O 3 ( u = 1 3 ) in the literature.