Elastic and anelastic anomalies associated with the antiferromagnetic ordering transition in wüstite, Fe x O

Zhang, Zhiying and Church, Nathan and Lappe, Sophie-Charlotte L. L. and Reinecker, Marius and Fuith, Armin and Saines, Paul J and Harrison, Richard J. and Schranz, Wilfried and Carpenter, Michael A. (2012) Elastic and anelastic anomalies associated with the antiferromagnetic ordering transition in wüstite, Fe x O. Journal of Physics: Condensed Matter, 24 (21). p. 215404. ISSN 0953-8984, 1361-648X DOI 10.1088/0953-8984/24/21/215404

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Abstract

The elastic and anelastic properties of three different samples of Fex O have been determined in the frequency range 0.1–2 MHz by resonant ultrasound spectroscopy and in the range 0.1–50 Hz by dynamic mechanical analysis in order to characterize ferroelastic aspects of the magnetic ordering transition at TN ∼ 195 K. No evidence was found of separate structural and magnetic transitions but softening of the shear modulus was consistent with the involvement of bilinear coupling, λe4 q, between a symmetry-breaking strain, e4 , and a structural order parameter, q. Unlike a purely ferroelastic transition, however, C44 does not go to zero at the ∗ critical temperature, Tc , due to the intervention of the magnetic ordering at a higher temperature. The overall pattern of behaviour is nevertheless consistent with what would be expected for a system with separate structural and magnetic instabilities, linear–quadratic coupling between the structural (q) and magnetic (m) driving order parameters, λqm2 , and ∗ TN > Tc . Comparison with data from the literature appears to confirm the same pattern in ∗ MnO and NiO, with a smaller difference between TN and Tc in the former and a larger difference in the latter. Strong attenuation of acoustic resonances at high frequencies and a familiar pattern of attenuation at low frequencies suggest that twin walls in the rhombohedral phase have typical ferroelastic properties. Acoustic dissipation in the stability field of the cubic phase is tentatively attributed to anelastic relaxations of the defect ordered structure of non-stoichiometric w ̈ stite or of the interface between local regions of w ̈ stite and magnetite, u u with a rate controlling step determined by the diffusion of iron.

Item Type: Article
Uncontrolled Keywords: 2012AREP; IA63;
Subjects: 03 - Mineral Sciences
Divisions: 03 - Mineral Sciences
Journal or Publication Title: Journal of Physics: Condensed Matter
Volume: 24
Page Range: p. 215404
Identification Number: 10.1088/0953-8984/24/21/215404
Depositing User: Sarah Humbert
Date Deposited: 27 Jun 2012 14:52
Last Modified: 23 Jul 2013 10:04
URI: http://eprints.esc.cam.ac.uk/id/eprint/2549

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