Abstract
We have investigated the mechanically induced self-propagating reaction between Fe 2O 3 and Al. In this reaction the final phases, Al 2O 3 and Fe, are formed by an in situ chemical reaction. The evolution of the system was characterized as a function of the milling time using X-ray diffraction, magnetometry (300 and 5 K) and Mössbauer spectroscopy (300 and 77 K). After reaction, Fe particles in a crystalline Al 2O 3 matrix have been formed. At larger milling times, a rather wide Fe grain size distribution of around 20 nm was obtained according to the diffraction patterns. Mössbauer spectra were constituted of both paramagnetic and ferromagnetic contributions. The former was attributed to small grains of superparamagnetic Fe (within the Mössbauer characteristic time τ M≈10 −8 s) and FeAl 2O 4, whereas the latter was associated to larger Fe grains. Saturation magnetization, coercivity field and remanent magnetization rapidly reached a stationary value with the milling time. A correlation between the microstructural characteristics of the sample and its magnetic properties before and after reaction is described.
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