Microstructural and magnetic characterization of nanostructured alpha-Fe2O3 and CuO mixtures obtained by ball milling

We have subjected powder mixtures of (0.5x)alpha -Fe2O3 and (1 - x) CuO to ball milling for a fixed period of 10 h for several x across the whole rang e of concentrations. No phases other than the initial ones in their nanostr uctural form were detected within the resolution of the several experimenta l techniques employed. The grain size of the CuO nanoparticles is not obser ved to depend notably upon x and the microstrain is three times higher than that found for haematite, In contrast, the alpha -Fe2O3 grain size varies with the haematite content of the mixtures and a minimum size of D approxim ate to 70 Angstrom was observed for 0.50 less than or equal to x less than or equal to 0.95. The high-field susceptibility can be expressed as the wei ghted sum of the milled CuO and alpha -Fe2O3 individual susceptibilities. F or low x, a Cu(Fe)O solid solution is formed. An increase in the overall ma gnetization is observed for intermediate concentrations. In addition, withi n this x range, a broad Mossbauer sextet related to grain boundary regions is found coexisting with a bulk alpha -Fe2O3 signal at 30 K. The relative a rea of this broad signal is a maximum for x = 0.67, a sample that also show s an anomalous magnetic hysteresis. We associate these facts to a state of spin disorder linked to the grain boundaries of the nanocrystalline materia l.