Characteristic low-temperature magnetic properties of aluminous goethite [α-(Fe, Al)OOH] explained

Date

2006-12-16

Authors

Liu, Qingsong
Yu, Yongjae
Torrent, José
Roberts, Andrew P.
Pan, Yongxin
Zhu, Rixiang

Journal Title

Journal ISSN

Volume Title

Publisher

American Geophysical Union

Abstract

Goethite (α-FeOOH) is an antiferromagnetic iron oxyhydroxide that forms as a weathering product of iron-bearing minerals. We systematically investigated the low- and room temperature properties of well-defined aluminous goethites [α-(Fe, Al)OOH] with varying grain size and Al content. A marked decrease in the Néel temperature with increasing Al content for goethite lowers the blocking temperature distribution, which produces an increase in the remanent magnetization on cooling. The zero-field-cooled (ZFC) and field-cooled (FC) curves are irreversible. This is due to an additional partial thermal remanent magnetization (pTRM), which is acquired at low temperatures during the FC process because the initial 300 K remanence is far from being saturated due to the extremely high saturation field of goethite. This pTRM can be thermally demagnetized when reheating a sample back to 300 K. Finally, a sharp decrease in the bulk coercivity at 11–13 mol % Al is mostly caused by a broad coercivity distribution due to nonuniformity of Al substitution, which becomes more significant with increasing Al content. The positive correlation between pTRM acquisition during the FC process and the bulk coercivity strongly indicates that the ZFC/FC behavior is controlled by the bulk coercivity, which is, in turn, determined by Al substitution. This explanation of the characteristic low-temperature magnetic properties of Al goethite provides important constraints for identifying natural Al goethite bearing samples and quantitatively estimating the contributions of this mineral to the bulk magnetic properties of such samples

Description

Keywords

magnetism, goethite, aluminum, low- temperature magnetic techniques

Citation

Source

Journal of Geophysical Research 111 (2006): B12S34/1-12

Type

Journal article

Book Title

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Access Statement

Open Access

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