Time-Asymmetric FORC Diagrams: A New Protocol for Visualizing Thermal Fluctuations and Distinguishing Magnetic Mineral Mixtures
Time-Asymmetric FORC Diagrams: A New Protocol for Visualizing Thermal Fluctuations and Distinguishing Magnetic Mineral Mixtures
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时间不对称 FORC 图：一种用于可视化热波动和区分磁性矿物混合物的新协议
DOI：
10.1029/2018gc007669
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发表时间：
2018
期刊：
影响因子：
--
通讯作者：
Badejo Sijibomioluwa
中科院分区：
文献类型：
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作者：
Berndt Thomas;Chang Liao;Wang Shishun;Badejo Sijibomioluwa
如今，一阶反转曲线（FORC）通常用于评估磁性矿物的磁畴状态和静磁相互作用。虽然在样品表征方面比体磁测量向前迈出了一大步，但 FORC 图和剩磁行为之间缺乏联系：FORC 图主要揭示磁域状态，而剩磁行为主要由热激活控制。我们提出了一种新工具，可以在所谓的时间不对称 (TA) FORC 图中可视化热波动。 TA-FORC 与传统 FORC 的不同之处在于，它们维持反转场 Ha 的时间（分钟）比 FORC 测量场 Hb（毫秒）更长。在这段延长的保持时间内，热激活导致一些磁性颗粒改变其磁化强度，从而导致 FORC 图向上移动。这种转变的幅度可以深入了解矿物的热粘稳定性及其剩磁获取行为。这不仅可以区分 FORC 图中的热粘性效应与静磁（即相互作用/磁畴状态相关）效应，而且还提供了一种分离磁性矿物混合物的方法：具有相似矫顽力谱的两种矿物在传统 FORC 图中完全重叠，在 TA-FORC 图中显示出不同的向上移动，在某些情况下可以在视觉上完全分离矿物。这有效地为样品中的两种磁性成分（例如不同晶粒尺寸、晶粒形状和/或矿物的两个晶粒群体）提供了两个独立的FORC特征。
First‐order reversal curves (FORCs) are nowadays routinely used to assess domain states and magnetostatic interactions of magnetic minerals. While a huge step forward from bulk magnetic measurements in terms of sample characterization, there is amissing linkbetween the FORC diagrams and remanence behavior: FORC diagrams mainly reveal domain states, while remanence behavior is largely controlled by thermal activations. We present a new tool to visualize thermal fluctuations in so‐called time‐asymmetric (TA) FORC diagrams. TA‐FORCs differ from traditional FORCs in that they maintain the reversal fieldHafor a longer time (minutes) than the FORC measurement fieldHb(milliseconds). During this extended hold time, thermal activations cause some magnetic grains to change their magnetization, giving rise to an upward shift in the FORC diagram. The magnitude of this shift gives insight into the thermoviscous stability of the mineral and its remanence acquisition behavior. This not only allows to distinguish thermoviscous effects in FORC diagrams from magnetostatic (i.e., interactions/domain state related) effects but also provides a way to separate mixtures of magnetic minerals: two minerals with similar coercivity spectra that would totally overlap in traditional FORC diagrams show different upward shifts in TA‐FORC diagrams, which in some cases enable complete separation of the minerals visually. This effectively provides two independent FORC signatures for two magnetic constituents in a sample such as two grain populations of different grain sizes, grain shapes, and/or mineral.