Magnetic Properties of $γ-Fe_2O_3$ Nanopowder Synthesized by Atmospheric Microwave Torch Discharge

A nanopowder containing $γ-Fe_2O_3$ particles was synthesized by adding a gas mixture of $H_2//Fe(CO)_5$ into a microwave torch discharge at 1 bar. The presence of $γ-Fe_2O_3$ phase was confirmed by powder X-ray diffraction (mean crystallite size $d_{XRD}$=24 nm). The dominating characteristic sextets of $γ-Fe_2O_3$ were identified in the Mössbauer spectrum taken at 5 K. The presence of pure $Fe_3O_4$ in the nanopowder was excluded. The Mössbauer spectrum taken at 5 K exhibited six times larger total spectrum area than the Mössbauer spectrum taken at 293 K. Zero field cooled/field cooled curves measured down to 4 K in the magnetic field of 7.9 kA/m are reported.