Synthesis and magnetic properties of concentrated α-Fe 2O 3 nanoparticles in a silica matrix

Abstract

Hematite nanoparticles in a silica matrix containing 30 wt.% of hematite were synthesized by the sol–gel method. Transmission electron microscopy studies showed that the average particle size of the hematite was about 4 nm with a narrow size distribution, while selected area electron diffraction confirmed the formation of the hematite phase. Investigation of the magnetic properties by DC magnetization and AC susceptibility measurements indicated behavior typical of a superparamagnetic system, such as the existence and frequency dependence of a blocking temperature, irreversibility of the zero-field-cooled (ZFC) and field-cooled (FC) curves, and emergence of magnetic hysteresis below the blocking temperature. Quantitative analysis of the DC magnetic data indicated that the system consisted of an assembly of superparamagnetic nanoparticles with a narrow size distribution, while the AC data implied the existence of weak inter-particle interactions.