Physics and Chemistry of Minerals

, Volume 12, Issue 6, pp 370–378 | Cite as

Magnetic properties of sheet silicates; 2:1:1 layer minerals

  • O. Ballet
  • J. M. D. Coey
  • K. J. Burke
Article

Abstract

Magnetization, susceptibility and Mössbauer spectra are reported for representative chlorite samples with differing iron content. The anisotropy of the susceptibility and magnetization of a clinochlore crystal is explained using the trigonal effective crystal-field model developed earlier for 1:1 and 2:1 layer silicates, with a splitting of theT2g triplet of 1,120K. Predominant exchange interactions in the iron-rich samples are ferromagnetic withJ=1.2 K, as for other trioctahedral ferrous minerals. A peak in the susceptibility of thuringite occurs atTm=5.5 K, and magnetic hyperfine splitting appears at lower temperatures in the Mössbauer spectrum. However neutron diffraction reveals no long-range magnetic order in thuringite (or biotite, which behaves similarly). The only magnetic contribution to the diffraction pattern at 1.6 K is increased small angle scattering (q<0.4 Å−1). A factor favouring this random ferromagnetic ground state over the planar antiferromagnetic state of greenalite and minnesotaite is the presence of pairs of ferric ions on adjacent sites, in conjunction with magnetic vacancies in the octahedral sheets. Monte Carlo simulations of the magnetic ground state of the sheets illustrate how long range ferromagnetic order may be destroyed by vortices forming around the Fe3+-Fe3+ pairs.

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Copyright information

© Springer-Verlag 1985

Authors and Affiliations

  • O. Ballet
    • 1
  • J. M. D. Coey
    • 1
  • K. J. Burke
    • 1
  1. 1.Department of Pure and Applied PhysicsTrinity CollegeDublin 2Ireland
  2. 2.Institut für Kristallographie und MineralogieUniversität Frankfurt am MainFrankfurtWest Germany

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