Electron spin resonance applied to nanosized-doped oxides

The electron spin resonance (ESR or EPR) is a spectroscopic technique particularly suited to investigate solid paramagnetic samples like powders composed of nanosized paramagnetic particles. In this chapter we review ESR investigations on samples of this kind. The effects of doping oxidic nanoparticles by metal cations or by nonmetal species are shown in the first paragraph. ESR can provide information on the energy of the unpaired electron and on the crystal field around it. When two or more unpaired electrons are present on a paramagnetic system, their reciprocal interactions supply important information on nature and distribution of dopant magnetic ions. Moreover, compositional fluctuations at the nanometric scale can induce the formation of extended clusters of magnetic ions. Systems of this kind are discussed in the second and third paragraph of the chapter.