XRD, internal field-NMR and Mössbauer spectroscopy study of composition, structure and magnetic properties of iron oxide phases in iron ores

Abstract

We report the phase-composition, structure and magnetic properties of two representative samples of naturally available iron-oxide containing ores/soils collected from two different regions in Karnataka, India. Presence of elements such as Fe, Si, Al and O were identified in both the samples using energy dispersive analysis of X-rays (EDAX). X-ray diffraction results confirmed that different ceramic phases such as crystalline iron oxide phases (Fe3O4, γ-Fe2O3 and α-Fe2O3), aluminosilicates (Al2SiO5) and low-quartz (SiO2) phases constitute the soil. The presence of ferrimagnetic phases (Fe3O4, γ-Fe2O3) makes the soil respond to a permanent magnet. Separation between the magnetic and non-magnetic phases was performed using a permanent magnet. The non-magnetic part of the sample contains a high amount of α-Fe2O3 phase along with aluminosilicates and low-quartz. The magnetic phases were further characterized and quantified. The presence of Fe3O4 phase in the samples was confirmed from the Verwey transition observed by internal-field NMR spectroscopy. Our results demonstrate that internal-field NMR and Mössbauer spectroscopy are complementary tools for characterizing iron containing soils. Furthermore, we found that the soil collected from the low temperature region (Sandur) contains more amounts of ferrimagnetic oxide (Fe3O4, γ-Fe2O3) phases, whereas the high temperature region (Hospete) contains more α-Fe2O3 phase. Hence, our results confirm that the phase composition of the soil is intimately related to the local daily temperature.