Spin orientation in solid solution hematite-ilmenite

Erik Brok, Cathrine Frandsen, Kim Lefmann, Suzanne McEnroe, Peter Robinson, Benjamin P. Burton, Thomas C. Hansen, Richard Harrison

Research output: Contribution to journalArticle

3 Citations (Scopus)

Abstract

The spin orientation in synthetic hematite-ilmenite samples and in a sample of natural hematite was studied from room temperature to above the antiferromagnetic-paramagnetic phase transition (the Néel temperature; TN ≈ 600-950 K) by neutron powder diffraction and at room temperature by Mössbauer spectroscopy. The usually assumed magnetic structure of hematite within this temperature range is antiferromagnetic with the spins confined to the basal plane of the hexagonal structure; however, an out-of-plane spin component is allowed by the symmetry of the system and has been observed in recent studies of synthetic hematite samples. We find the spins in the antiferromagnetic sublattices to be rotated out of the basal plane by an angle between 11(2)° and 22.7(5)° in both synthetic hematite-ilmenite samples and in the natural hematite sample. The spin angle remains tilted out of the basal plane in the entire temperature range below the Néel temperature and does not depend systematically on Ti-content. The results indicate that the out-of-plane spin component is an intrinsic feature of hematite itself, with an origin not yet fully understood, but consistent with group theory. This represents a major shift in understanding of one of the two main mineral systems responsible for rock magnetism.

Original languageEnglish
Pages (from-to)1234-1243
Number of pages10
JournalAmerican Mineralogist
Volume102
Issue number6
DOIs
Publication statusPublished - 1 Jun 2017
Externally publishedYes

Keywords

  • Hematite
  • magnetic properties
  • spin orientation
  • neutron scattering
  • Mössbauer spectroscopy

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