Models of Maghematization: Observational Evidence in Support of a Magnetic Unstable Zone
Models of Maghematization: Observational Evidence in Support of a Magnetic Unstable Zone
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DOI：
10.1029/2020gc009504
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发表时间：
2021-02
期刊：
影响因子：
3.7
通讯作者：
K. Ge;W. Williams;L. Nagy;L. Tauxe
中科院分区：
文献类型：
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作者：
K. Ge;W. Williams;L. Nagy;L. Tauxe
最近的微磁学模拟预测，颗粒有一个异常的区域，从单畴到单涡的畴态转变附近的晶粒尺寸的低磁稳定性。这个区域的含义尚未完全了解，但如果这个窗口的大小范围作为施加的场和温度的函数而变化，那么它很可能会导致古地磁记录中的观测不确定性。该区域的窄尺寸范围意味着当在样品中存在的更宽的粒度分布上整合时，其影响难以识别。本文报道了一种利用磁铁矿低温氧化研究不稳定区的方法。使用多层核壳结构的微磁学模拟重新解释了中值直径接近不稳定区的部分氧化颗粒的岩石磁性实验。预测的磁性能表现出显着改善的协议与实验数据比以前报道的单核壳耦合的几何形状。观察到的剩磁和矫顽力的变化与预测的磁畴结构的变化附近的一个拟议的磁不稳定区（180 - 120 nm），因此提供了第一个实验表明存在这样一个区域。我们还表明，在这个尺寸范围之外的颗粒的剩磁是稳定的磁化。该研究为“磁不稳定区”的实验研究提供了思路，对磁记录的正确解释具有重要意义。最后，部分氧化的磁铁矿颗粒能够记录古地磁信号。
Recent micromagnetic simulations predict that particles have an abnormal region of low magnetic stability for grain sizes near the domain state transitions from single domain to single vortex. The implications of this zone are not yet fully understood, but if the size range of this window changes as a function of applied field and temperature then it is likely to contribute to observational uncertainties in paleomagnetic recordings. The narrow size range of this zone means that its effects are difficult to identify when integrated across the much wider distribution of grain sizes present in a sample. Here we report a method of examining the unstable region using low temperature oxidation of magnetite. The rock magnetic experiments on partially oxidized particles with a median diameter close to the unstable zone are reinterpreted using micromagnetic simulations of a multilayer core‐shell structure. The predicted magnetic properties exhibit significantly improved agreement with experimental data than that of the previously reported single core‐shell coupled geometry. The observed changes in remanence and coercivity are associated with predicted domain structure changes near a proposed magnetic unstable zone (∼80–∼120 nm), and so provide the first experimental indication of the existence of such a region. We also demonstrate that magnetic remanence in particles with grain sizes outside this size range were stable to maghemitization. The research provides ideas for the experimental study of the “magnetic unstable zone” and is significant to the correct interpretation of magnetic recordings. Finally, the partially oxidized magnetite particles are able to record paleomagnetic signals.