Magnetic properties of oxide-coated iron nanoparticles synthesized by electrodeposition

Nanometre-sized iron particles with diameters in the range 4.9-11.1 nm have been grown within a silica gel matrix by electrodeposition. Electron diffraction pattern shows the presence of an oxide (either Fe3O4 or gamma-Fe2O3) shell on these particles. The variation of magnetization as a function of temperature has been analyzed using the Bloch equation. The Bloch exponent obtained as a function of particle size shows a trend different from that predicted theoretically. Zero field cooled (ZFC) and field cooled (FC) measurements on the nanocomposites have been carried out over the temperature range 2-300 It. Coercivity shows a decrease with increasing temperature. Also, a loop shift as a function of temperature is exhibited by the specimens. This shift disappears at a temperature around 50 K. This behavior is ascribed to an exchange interaction of the iron core with a ferrimagnetic oxide (either Fe3O4 or gamma-Fe2O3) shell. (C) 2000 Elsevier Science B.V. All rights reserved.