Stewart, S. J.; Borzi, R. A.; Punte, G.; Mercader, R. G. and Garcia, F.
Microstructural and magnetic characterization of nanostructured alpha-Fe2O3 and CuO mixtures obtained by ball milling.
Journal of Physics: Condensed Matter, 13(8) pp. 1743–1757.
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 range of concentrations. No phases other than the initial ones in their nanostructural form were detected within the resolution of the several experimental techniques employed. The grain size of the CuO nanoparticles is not observed 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 approximate 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 weighted sum of the milled CuO and alpha -Fe2O3 individual susceptibilities. For low x, a Cu(Fe)O solid solution is formed. An increase in the overall magnetization is observed for intermediate concentrations. In addition, within 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 area of this broad signal is a maximum for x = 0.67, a sample that also shows an anomalous magnetic hysteresis. We associate these facts to a state of spin disorder linked to the grain boundaries of the nanocrystalline material.
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