High field magnetization of the colloidal Mn-Zn ferrite

The magnetic properties of a hydrocarbon based colloid (stabilized by oleic acid) of polydisperse chemically co-precipitated Mn0.5Zn0.5Fe2O4 pal-tides are discussed in the paper. Two fractions are separated from an initial fe rrofluid sample by centrifugation. X-ray diffraction measurements show the crystal structure of the particles and a broadened shape of the diffraction lines. Mean particle diameters 6.2 nm (the light fraction) and 9.7 nm (the heavy one) were determined by TEM measurements. The magnetization of the c olloids is measured by VSM up to 12 T. A significant slope in the magnetiza tion curves in the high field region is displayed for both samples in the t emperature interval from 100 to 295 K. Two methods are used to estimate the spontaneous magnetization of the material: a high field approximation of t he magnetization curve by M(H) = M,(1 - kT/mH) + xH and a decomposition of the magnetization curve in a spectrum of Langevin functions of varying magn etic moments. Both methods give practically identical results. Evaluation o f the spontaneous intrinsic magnetization shows a slight dependence of the relative pyromagnetic coefficient M(s)(-1)partial derivative M-s/partial de rivative T on particle size. (C) 1999 Elsevier Science B.V. All rights rese rved.