Effect of isomorphic substitutions on the Mössbauer and magnetic parameters of goethite

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Abstract
The effect of the isomorphic substitutions in the goethite structure on its magnetic and Mössbauer parameters was studied. For this purpose, synthetic samples of Al-substituted goethite with particle sizes of 24–28 nm were obtained and studied by means of Mössbauer spectroscopy, X-ray diffractometry, electron microscopy, and magnetic measurements. It was found that an increase in the number of isomorphic ions in the structure of this iron hydroxide reduces its susceptibility, magnetization, and the effective magnetic field of the nucleus. In addition, the structural substitutions of aluminum for iron ions leads to a significant decrease in the temperature of the magnetic phase transition (the Neel temperature). The way to explain the experimental results on the basis of the Neel theory in the nearest-neighbor approximation was considered. The possibility to use the obtained results for studying the genesis of iron oxides and hydroxides in soils was shown by the example of East African laterites.

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