Abstract
The present study investigates magnetic properties of interacting 12.4 nm Fe 3O 4 spinel ferrite particles. Fe 3O 4 crystallizes in cubic structure with lattice parameters, a=0.839(1) nm. Ultrafine nature of the materials were ascertained by the X-ray diffraction (XRD) line broadening and field dependent magnetic analysis. The 57Fe Mössbauer spectrum is deconvoluted to two sextets indicating two different Fe sites and a central doublet indicating superparamagnetic fractions present. The saturation magnetization (at 298 K), σ s=67.8 emu/g, is less than that of the bulk magnetic particles, i.e. σ s (bulk)=92 emu/g. The reduction of σ s in Fe 3O 4 particles is attributed to the presence of non-magnetic layer at the particle surface, cation distribution, superparamagnetic relaxation and spin canting because of the ultrafine nature of the material. The low field temperature dependence of magnetization below the Curie temperature, T c, shows two distinct peaks, i.e. at 615 and 800 K. The maximization in magnetization near T c and the decrease in T c are attributed to a large degree of inversion of the Fe 3O 4 particles. A peak at 615 K in low field thermomagnetic studies on the zero field cooled (ZFC) samples confirms the dipolar interactions to be dominant over superparamagnetic blocking.
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