Microstructural, electronic and magnetic characterization of Fe-based nanoparticles embedded in Al matrix

Highlights: • Novel granular Fe–Al thin films were grown by the gas-phase aggregation technique. • The progressive transition of structure and properties with change in composition, comprising iron, aluminum and oxygen, is shown. • Core–shell metal-oxide structures are formed for samples with high density of nanoparticles. • Core–shell Fe-alloy structures are developed in the case of low density of nanoparticles. • The magnetic behavior points to potential applications as high density recording media and permanent magnets Nominal granular iron oxide-aluminum thin films have been prepared by simultaneous deposition of iron oxide nanoparticles, grown by the gas-phase aggregation technique, and an aluminium matrix, grown by conventional magnetron sputtering. Composition, structure and magnetic behavior have been analyzed by different techniques including TEM and AFM microscopies, EDX, RBS, X-ray absorption and Mössbauer spectroscopies and SQUID magnetometry. Both, structure and magnetic behavior, are found to be highly dependent on the preparation conditions. In particular, our work shows that for low matrix/nanoparticle ratios the aluminum is able to partially displace the iron oxide and form a core–shell iron metal-iron oxide structure. For higher ratios, on the other hand, the oxygen atoms become very diluted and their role negligible. In this case a core–shell structure consisting of an iron metal core and an iron–aluminum alloy shell is formed. Magnetization measurements indicate that in the first case the core and the shell are magnetically coupled while in the second case the two phases are magnetically uncoupled, the Fe–Al alloy presenting strong coercivity.