Spin orientation in a natural Ti-bearing hematite: Evidence for an out-of-plane component

Harrison, Richard J. and McEnroe, Suzanne A. and Robinson, Peter and Howard, Christopher J. (2010) Spin orientation in a natural Ti-bearing hematite: Evidence for an out-of-plane component. American Mineralogist, 95 (7). pp. 974-979. DOI 10.2138/am.2010.3402

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Abstract

The orientation of spins in a natural sample of Ti-bearing hematite (Fe2O3) has been measured from 2-300 K using time-of-flight neutron powder diffraction. It is shown that the antiferromagnetic alignment vector is tilted out of the basal plane by an average angle of 30{degrees}, independent of temperature, contrary to the normal expectation that all spins lie in the basal plane due to the suppression of the Morin transition by Ti. This unusual result is related to the non-uniform spatial distribution of Ti in this sample, which takes the form of ~1 nm exsolution lamellae of ilmenite (FeTiO3), observed using transmission electron microscopy. It is suggested that the exsolution lamellae lead to a localization of Fe2+ species within the lamellar interfaces, which cause tilting of some spins toward the crystallographic c axis. The presence of an out-of-plane component of spin at room temperature reconciles experimental and computational attempts to explain the phenomenon of "giant exchange bias" that appears when this sample is zero-field cooled below the ilmenite Neel temperature.

Item Type: Article
Uncontrolled Keywords: 2010AREP; IA60;
Subjects: 03 - Mineral Sciences
Divisions: 03 - Mineral Sciences
Journal or Publication Title: American Mineralogist
Volume: 95
Page Range: pp. 974-979
Identification Number: 10.2138/am.2010.3402
Depositing User: Sarah Humbert
Date Deposited: 01 Sep 2011 07:29
Last Modified: 23 Jul 2013 10:02
URI: http://eprints.esc.cam.ac.uk/id/eprint/2176

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