Viscous magnetization of 0.04–100 μm magnetites
Viscous magnetization of 0.04–100 μm magnetites
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DOI：
10.1111/j.1365-246x.1983.tb01899.x
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发表时间：
1983-09
影响因子：
2.8
通讯作者：
D. Dunlop
中科院分区：
文献类型：
--
作者：
D. Dunlop
对平均粒径为0.04 - 0.22 μm的四种合成磁铁矿分散体和仅在室温下的另外六种样品（2-100 μm），测量了小场粘性磁化强度的获得和衰减随温度（9-500 ℃）的变化。室温粘性磁化在单畴范围内是明显的，在0.1和5 μm之间是轻微的，在中间的多畴范围内（10-15 μm）又是显著的。在所有实验中，采集速率超过衰减速率，导致零场衰减时间等于暴露于场的时间后残留未衰减粘性剩磁（VRM）。粘性磁化强度在升高的温度下增强，但与绝对温度不成正比。相反，似乎存在一个低温（< 20°C）阈值，在该阈值以下粘性效应可以忽略不计，并且在高温下接近饱和。在给定温度下等温产生的VRM通过加热到比大多数热激活理论预测的更高的温度而明显更难以擦除。此外，即使在非常简短的实验中，粘度系数S=| σJ| σlog t|随时间增加，在高温下增加更明显。这些观察结果的影响是，粘性叠印的天然reversible磁化在磁铁矿轴承岩石，特别是在埋葬或侵入再加热，可能是更广泛的，更难以消除比以前认为的。
Summary Acquisition and decay of small-field viscous magnetization have been measured as a function of temperature (9-500°C) for four synthetic magnetite dispersions ranging in mean particle size from 0.04 to 0.22 pand at room temperature only for an additional six samples (2-100 μm). Room-temperature viscous magnetization is pronounced in the single-domain range, slight between 0.1 and 5 μm, and again substantial in the intermediate multidomain range (10-15 μm). In all experiments, the acquisition rate exceeded the decay rate, resulting in residual undecayed viscous remanent magnetization (VRM) after a zero-field decay time equal to the time of exposure to a field. Viscous magnetization is enhanced at elevated temperatures but not in direct proportion to absolute temperature. Instead, there appears to be a low-temperature (< 20°C) threshold below which viscous effects are negligible and an approach to saturation at high temperature. VRM produced isothermally at a given temperature is significantly more difficult to erase by heating to a higher temperature than most thermal activation theories predict. Furthermore, even in quite brief experiments, the viscosity coefficient S= |σJ|σlog t| increased with time, the increase being more pronounced at high temperature. The implications of these observations are that viscous overprinting of natural remanent magnetization in magnetite-bearing rocks, particularly during burial or intrusive reheating, may be more extensive and more difficult to erase than previously believed.