Almeida Trevor P, Kasama Takeshi, Muxworthy Adrian R, Williams Wyn, Nagy Lesleis, Hansen Thomas W, Brown Paul D, Dunin-Borkowski Rafal E
Department of Earth Science and Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, UK.
Center for Electron Nanoscopy, Technical University of Denmark, Kongens Lyngby DK-2800, Denmark.
Nat Commun. 2014 Oct 10;5:5154. doi: 10.1038/ncomms6154.
Magnetite (Fe3O4) is an important magnetic mineral to Earth scientists, as it carries the dominant magnetic signature in rocks, and the understanding of its magnetic recording fidelity provides a critical tool in the field of palaeomagnetism. However, reliable interpretation of the recording fidelity of Fe3O4 particles is greatly diminished over time by progressive oxidation to less magnetic iron oxides, such as maghemite (γ-Fe2O3), with consequent alteration of remanent magnetization potentially having important geological significance. Here we use the complementary techniques of environmental transmission electron microscopy and off-axis electron holography to induce and visualize the effects of oxidation on the magnetization of individual nanoscale Fe3O4 particles as they transform towards γ-Fe2O3. Magnetic induction maps demonstrate a change in both strength and direction of remanent magnetization within Fe3O4 particles in the size range dominant in rocks, confirming that oxidation can modify the original stored magnetic information.
磁铁矿（Fe3O4）对地球科学家来说是一种重要的磁性矿物，因为它在岩石中具有主要的磁性特征，而对其磁记录保真度的理解为古地磁学领域提供了一个关键工具。然而，随着时间的推移，Fe3O4颗粒会逐渐氧化成磁性较弱的铁氧化物，如磁赤铁矿（γ-Fe2O3），从而使对其记录保真度的可靠解释大打折扣，剩余磁化强度随之改变，这可能具有重要的地质意义。在这里，我们使用环境透射电子显微镜和离轴电子全息术这两种互补技术，来诱导并可视化单个纳米级Fe3O4颗粒在向γ-Fe2O3转变过程中氧化对其磁化的影响。磁感应图表明，在岩石中占主导地位的尺寸范围内，Fe3O4颗粒内剩余磁化强度的大小和方向都发生了变化，这证实了氧化可以改变原始存储的磁信息。
