Microstructural and magnetic characterisation of nanostructured -Fe2O3 and CuO mixtures obtained by ball milling

SILVANA JACQUELINE STEWART; R. A. BORZI; G. PUNTE; R. C. MERCADER; F. GARCIA

Journal of Physics Condensed Matter

Año: 2001 vol. 13 p. 1743 - 1757

0953-8984

We have subjected powder mixtures of (0.5x)α-Fe2O3 and (1 − x)CuO to ballmilling for a fixed period of 10 h for several x across the whole range ofconcentrations. No phases other than the initial ones in their nanostructuralform were detected within the resolution of the several experimental techniquesemployed. The grain size of the CuO nanoparticles is not observed to dependnotably upon x and the microstrain is three times higher than that foundfor haematite. In contrast, the α-Fe2O3 grain size varies with the haematitecontent of the mixtures and a minimum size of D ≈ 70 Å was observedfor 0.50
x
0.95. The high-field susceptibility can be expressed asthe weighted sum of the milled CuO and α-Fe2O3 individual susceptibilities.For low x, a Cu(Fe)O solid solution is formed. An increase in the overallmagnetization is observed for intermediate concentrations. In addition, withinthis x range, a broad M¨ossbauer sextet related to grain boundary regions isfound coexisting with a bulk α-Fe2O3 signal at 30 K. The relative area of thisbroad signal is a maximum for x = 0.67, a sample that also shows an anomalousmagnetic hysteresis. We associate these facts to a state of spin disorder linkedto the grain boundaries of the nanocrystalline material.