Chapter 10 - Applications of electron magnetic resonance in the study of soils, minerals, and iron oxides

Abstract

Abstract Iron oxides shows magnetic properties and are very common compounds present in soils and rocks. Electron magnetic resonance (EMR) is a reliable technique to study these properties when associated with other techniques such as magnetometry, Mossbauer spectroscopy and others. Thus, in this chapter we show how to obtain information from EMR spectroscopy from mineral samples both theoretically and experimentally. The minerals from Araucaria site (Parana state, Brazil) were separated by particle size fractionation and investigated by EMR at room temperature and 77K. The paramagnetic species in the soil samples were identified by comparison with EMR spectra of some minerals studied by our group, and several soil types and/or soil components investigated in the literature. Besides the study of paramagnetic species in soils, the iron oxide goethite was studied in more details. Goethite, despite its antiferromagnetic behavior, shows a magnetic component. The origin of the mechanism that create this magnetic component has been discussed in literature for about half of century. EMR was applied to different samples of goethite, natural and synthetic. It was studied the magnetic transition to the paramagnetic state that the mineral undergoes with increasing temperature. Besides, with different synthesis, it was related the magnetic properties, as analyzed by EMR results, with structural characteristics.