Analysis on variety and characteristics of maghemite

作     者：SHAW John BLOEMENDAL Jan HESSE Paul ROLPH Tim 

作者机构：Department of Earth SciencesUniversity of Liverpool Department of GeographyUniversity of Liverpool Department of Environment and GeographyMacquarie University Department of GeologyUniversity of Newcastle 

出 版 物：《Science China Earth Sciences》 (中国科学（地球科学英文版）)

年 卷 期：2010年第53卷第8期

页      面：1153-1162页

核心收录：

学科分类：080602[工学-钢铁冶金] 08[工学] 0806[工学-冶金工程] 0708[理学-地球物理学] 0704[理学-天文学] 

基　　金：supported by the Science and Engineering Research Council, UK recently has been supported by the National Natural Science Foundation of China (Grant Nos.40772109, 40830105,40911120072,40721061) Research Grant of Education Ministry (Grant No.20070730026) an Initial Research Grant supported by Lanzhou University 

主　　题：maghemite paleomagnetism environmental magnetism magnetic mineral thermal stability TRM 

摘      要：Maghemite (γ-Fe2O3) is a very common mineral at the earth’s surface and also an important material for making music and video tapes. Maghemite is usually synthesized from magnetite under oxidizing conditions after a few hours or a few days below a temperature of 300°C. The magnetic property of thermal instability and the chemical action after heating is an important character for maghemite. That is, it will become hematite in certain proportion after being heated above 250°C. Maghemite is therefore actually unable to have its Curie temperature measured. But late using synthetic sample, maghemite was further found partially thermal stable with a measurable Curie temperature ~645°C. During our thermally magnetic experiments for a set of synthetic magnetite, we found that extra fined grain size (pseudo single domain (PSD) and small multi-domain (MD), mainly 1-10 μm) magnetite was formed to a completely thermally stable maghemite. This maghemite can also be produced by heating the same powder up to 700°C in an oven and keeping this temperature for 10 min, then cooling it down. When the generated maghemite by these two ways is heated from room temperature to 700°C, it shows almost fully reversible, or thermally stable. We used X-ray powder diffraction and Mssbauer spectroscopy to confirm the identity of this maghemite and compared its magnetic hysteresis, high temperature magnetization, low temperature thermal demagnetization, and low temperature susceptibility with those of the original preheated magnetite. Such quickly oxidized maghemite by heating to high temperature implies some types of maghemite formed in certain natural condition can carry a thermal remnant magnetization (TRM). Four types of maghemite were characterized and discussed according to their thermal stability. Among them, partially stable and fully thermally stable maghemite after heating should possess capability of carrying TRM. There is possibly a compensation of synthetizing maghemite between heatin