title: Origin of Magnetism in Hydrothermally Aged 2-Line Ferrihydrite Suspensions.
abstract: As an iron oxyhydroxide, nanosized ferrihydrite (Fh) is important in Earth science, biology, and industrial applications. However, its basic structure and origin of its magnetism have long been debated. We integrate synchrotron-based techniques to explore the chemical structures of 2-line ferrihydrite and to determine the origin of its magnetism during hydrothermal aging in air. Our results demonstrate that both the magnetism and X-ray magnetic circular dichroism (XMCD) signal of 2-line ferrihydrite are enhanced with aging time, and that XMCD spectral patterns resemble that of maghemite (γ-Fe2O3) rather than magnetite (Fe3O4). Fe L-edge and K-edge X-ray absorption spectroscopy (XAS) further indicate formation of both maghemite and hematite (α-Fe2O3) with increasing concentrations with longer hydrothermal aging time. Thus, magnetic enhancement with longer hydrothermal aging time is attributed to increasing maghemite concentration instead of a magnetically ordered ferrihydrite as previously reported. Moreover, L-edge and K-edge XAS spectra with different probing depths yield different ratios of these Fe oxides, which suggest the formation of a core (ferrihydrite-rich)-shell (with a mixture of both allotropes; α-Fe2O3and γ-Fe2O3) structure during hydrothermal aging. Our results provide insights into the chemical evolution of 2-line ferrihydrite that reveal unambiguously the origin of its magnetism.
authors.affiliation: Shanghai Institute of Applied Physics, Chinese Academy of Sciences , P.O. Box 800-204, Shanghai, 201800, P. R. China.|High Magnetic Field Laboratory, Chinese Academy of Sciences , 350 Shushanhu Road, Hefei, Anhui, 230031, P. R. China.
authors.forename: Liang
authors.identifier: 0000-0001-7453-7060
authors.initials: L
authors.lastname: Cao
authors.affiliation: State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences , 19 Beitucheng Western Road, Beijing, 100029, P. R. China.
authors.forename: Zhao-Xia
authors.initials: ZX
authors.lastname: Jiang
authors.affiliation: Institute of Chemical and Engineering Sciences , A*STAR (Agency for Science, Technology and Research), 1 Pesek Road, Jurong Island, 627833, Singapore.
authors.forename: Yong-Hua
authors.identifier: 0000-0003-2655-045X
authors.initials: YH
authors.lastname: Du
authors.affiliation: Department of Physics, National University of Singapore , 2 Science Drive 3, 117542, Singapore.|SZU-NUS Collaborative Innovation Center for Optoelectronic Science & Technology, Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University , Shenzhen, 518060, P. R. China.
authors.forename: Xin-Mao
authors.initials: XM
authors.lastname: Yin
authors.affiliation: Institute of Chemical and Engineering Sciences , A*STAR (Agency for Science, Technology and Research), 1 Pesek Road, Jurong Island, 627833, Singapore.
authors.forename: Shi-Bo
authors.initials: SB
authors.lastname: Xi
authors.affiliation: Shanghai Institute of Applied Physics, Chinese Academy of Sciences , P.O. Box 800-204, Shanghai, 201800, P. R. China.
authors.forename: Wen
authors.initials: W
authors.lastname: Wen
authors.affiliation: Research School of Earth Sciences, The Australian National University , 142 Mills Road, Canberra, ACT 2601, Australia.
authors.forename: Andrew P
authors.initials: AP
authors.lastname: Roberts
authors.affiliation: Department of Physics, National University of Singapore , 2 Science Drive 3, 117542, Singapore.
authors.forename: Andrew T S
authors.initials: AT
authors.lastname: Wee
authors.affiliation: High Magnetic Field Laboratory, Chinese Academy of Sciences , 350 Shushanhu Road, Hefei, Anhui, 230031, P. R. China.
authors.forename: Yi-Min
authors.initials: YM
authors.lastname: Xiong
authors.affiliation: Department of Marine Science and Engineering, Southern University of Science and Technology of China , Shenzhen, 518055, P. R. China.|Laboratory for Marine Geology, Qingdao National Oceanography Laboratory for Science and Technology , Qingdao, 266071, P. R. China.
authors.forename: Qing-Song
authors.initials: QS
authors.lastname: Liu
authors.affiliation: Shanghai Institute of Applied Physics, Chinese Academy of Sciences , P.O. Box 800-204, Shanghai, 201800, P. R. China.
authors.forename: Xing-Yu
authors.initials: XY
authors.lastname: Gao
mesh_terms: D005290:Ferric Compounds / Q000737:chemistry*; D008280:Magnetics; D013535:Suspensions; D056928:X-Ray Absorption Spectroscopy; D014965:X-Rays
chemical_list: D005290:Ferric Compounds; D013535:Suspensions