Magnetic particles goethite

Booy M. Swaddle, T.W. (1978) Hydrothermal preparation of magnetite from iron chelates. Can. J. Chem. 56 402-403 Boquet, S. Pollard, R.J. Cashion, J.D. (1990) Dynamic magnetic phenomena in fine particle goethite. Phys. Rev. B46 11657-11664... 

In relation to goethite, the room temperature magnetic hyperfine fields are always below 38.0 T, which is the reference value of well-crystallized large-particle goethite [21,22]. The low hyperfine field values may be related to the small grain sizes as well as the alteration of the Fe neighboring due to anion and/or cation substitutions. 

Due to the similar ionic radius (0.62 A [338]) and the existence of isostructural oxyhydroxide (GaOOH), Ga ions substituted Fe " " in the structure of goethite in a broad concentration range [300]. Ga-for-Fe substitution in the structure of goethite affects the reduction in HMF and Neel temperature due to magnetic dilution by nonmagnetic Ga " ions and to the formation of small Ga-goethite particles. 

Similarly as for goethite, a linear relationship of R as a function of A1 content and particle size has been proposed [ 102] which is valid at RT and for concentrations less than 10 %A1. However, all these results are derived from synthetic samples, mostly obtained from goethite. Therefore, particularly at RT, the magnetic hyperfine field will still be largely influenced by morphological effects. Moreover, most preparation methods, based on the decomposition of oxyhydroxides, result in inhomogeneous A1 substitution [96]. A more clear-cut picture for the dependence of the hyperfine field on A1 substitution is obtained for hematites prepared from oxinates [103] where a reduction of 0.061 at RT and 0.032 at 80 K per at % A1 is observed. 

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