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Magnetic properties and site occupancy of iron in nontronite

Published online by Cambridge University Press:  09 July 2018

P. R. Lear  and
J. W. Stucki
P. R. Lear
Affiliation:
University of Illinois, Urbana, IL 61801 USA
J. W. Stucki
Affiliation:
University of Illinois, Urbana, IL 61801 USA
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Abstract

The magnetic susceptibilities of seven different nontronites in their natural oxidation states were measured between 5 and 100 K. Results revealed that the magnetic exchange interaction in all samples was antiferromagnetic, except no clear minimum occurred at the Néel temperature. Possible explanations for this phenomenon which are discussed include magnetic dilution due to isomorphous substitution, and antiferromagnetic frustration due to either non-centrosymmetric distribution of octahedral Fe3+ or tetrahedral Fe3+ substitution. A computer simulation model was developed to demonstrate the effects of these variables on long-range magnetic ordering. Magnetic dilution and tetrahedral Fe3+ content could explain the anomalous antiferromagnetic behaviour in some, but not all, samples. The non-centrosymmetric model is the only one which explains the behaviour of all samples. In this model, at least 13% of the octahedral Fe3+ would occupy trans-dihydroxide sites, with the balance in cis sites. Magnetic frustration occurs because two Fe3+ neighbours of a third Fe3+ ion are also neighbours to each other, making the simultaneous satisfaction of all antiferromagnetic exchange interactions impossible.

Type
Research Article
Information
Clay Minerals , Volume 25 , Issue 1 , March 1990 , pp. 3 - 13
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1990

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