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Magnetism of Al‐substituted magnetite reduced from Al‐hematite
Author(s) -
Jiang Zhaoxia,
Liu Qingsong,
Zhao Xiang,
Roberts Andrew P.,
Heslop David,
Barrón Vidal,
Torrent José
Publication year - 2016
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.983
H-Index - 232
eISSN - 2169-9356
pISSN - 2169-9313
DOI - 10.1002/2016jb012863
Subject(s) - hematite , magnetite , goethite , coercivity , materials science , mineralogy , curie temperature , magnetism , quartz , chemical engineering , geology , analytical chemistry (journal) , metallurgy , chemistry , ferromagnetism , environmental chemistry , adsorption , physics , organic chemistry , condensed matter physics , engineering , quantum mechanics
Aluminum‐substituted magnetite (Al‐magnetite) reduced from Al‐substituted hematite or goethite (Al‐hematite or Al‐goethite) is an environmentally important constituent of magnetically enhanced soils. In order to characterize the magnetic properties of Al‐magnetite, two series of Al‐magnetite samples were synthesized through reduction of Al‐hematite by a mixed gas (80% CO 2 and 20% CO) at 395°C for 72 h in a quartz tube furnace. Al‐magnetite samples inherited the morphology of their parent Al‐hematite samples, but only those transformed from Al‐hematite synthesized at low temperature possessed surficial micropores, which originated from the release of structural water during heating. Surface micropores could thus serve as a practical fingerprint of fire or other high‐temperature mineralogical alteration processes in natural environments, e.g., shear friction in seismic zones. In addition, Al substitution greatly affects the magnetic properties of Al‐magnetite. For example, coercivity ( B c ) increases with increasing Al content and then decreases slightly, while the saturation magnetization ( M s ), Curie temperature ( T c ), and Verwey transition temperature ( T v ) all decrease with increasing Al content due to crystal defect formation and dilution of magnetic ions caused by Al incorporation. Moreover, different trends in the correlation between T c and B c can be used to discriminate titanomagnetite from Al‐magnetite, which is likely to be important in environmental and paleomagnetic studies, particularly in soil.