Structure of iron oxide nanoparticles studied by 57Fe NMR

Abstract

In this work we apply nuclear magnetic resonance (NMR) spectroscopy of 57Fe nuclei for investigation of submicron and nanocrystalline iron oxide systems. The studied iron oxide particles are obtained from ferrous hydroxide gels (prepared from FeCl2 and KOH) by aging at elevated temperatures (90 C) with KNO3 as oxidant. The 57Fe NMR spectra of the samples are measured in temperature range 4.2-370 K in a zero external magnetic field. Signals of 57Fe nuclei assigned to tetrahedral and octahedral iron sites are well resolved. The NMR spectra and their temperature dependences are compared with those of stoichiometric and nonstoichiometric magnetite single crystals, as well as with samples of maghemite.