Characterization of Nanosized Maghemite Particles Prepared by Microemulsion Using an Ionic Surfactant

摘要

We have characterized a system of maghemite, γ-Fe_2O_3, nanosized particles prepared by a microemulsion method using an ionic surfactant. The M?ssbauer spectra from 21 to 298 K evolve from a totally magnetically split signal at low temperatures to a single superparamagnetic (sp) doublet at 298 K with a blocking temperature of ≈150 K. The real component of the AC susceptibility (5 ≤ ν ≤ 10~4 Hz) displays a behavior characteristic of a system of interacting particles. A broad distribution of the particle sizes is revealed by the much higher average energy barrier obtained by AC susceptibility than Mossbauer.