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Grain size dependence of low-temperature remanent magnetization in natural and synthetic magnetite: Experimental study

机译：天然和合成磁铁矿中低温剩磁的粒度依赖性：实验研究

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Magnetic measurements at cryogenic temperatures (<300 K) proved to be useful in paleomagnetic and rock magnetic research, stimulating continuous interest to low-temperature properties of magnetite and other magnetic minerals. Here I report new experimental results on a grain size dependence of the ratio (RLT) between a low-temperature (20 K) saturation isothermal remanent magnetization (SIRM) imparted in magnetite after cooling in a 2.5 T field (field cooling, FC) and in a zero field environment (zero field cooling, ZFC). Synthetic magnetite samples ranged in mean grain size from 0.15 to 100 μm, representing nearly single-domain (SD), pseudosingle-domain (PSD), and multidomain (MD) magnetic states. The RLT ratio monotonically increases from 0.58 to 1.12 with the decreasing mean grain size, being close to unity for PSD grains (0.15-5 μm) and smaller than unity for MD magnetite (12-100 μm). The RLT ratio of 1.27 is observed for acicular magnetite characterized by nearly SD behavior. These observations indicate that within the range of ～0.15 to ～5 μm, the low-temperature SIRM may be higher than that expected from "normal" magnetic domain wall displacement. Such a behavior can be caused by the presence of a SD-like component in the magnetization of these grains, which origin, however, is uncertain. The natural rocks containing nearly stoichiometric magnetite manifest a dependence of the RLT ratio on magnetic domain state identical to that observed from synthetic magnetites. Therefore, the comparison of FC SIRM and ZFC SIRM at very low temperatures may allow a crude estimate of magnetic domain state in some magnetite-bearing rocks, such as shallow mafic intrusions or some marine sediments.
机译：事实证明，在低温（<300 K）下进行磁测量可用于古磁和岩石磁研究，从而激发了人们对磁铁矿和其他磁性矿物的低温特性的持续关注。在这里，我报告了在2.5 T磁场（磁场冷却，FC）中冷却后，磁铁矿中的低温（20 K）饱和等温剩余磁化强度（SIRM）与晶粒之间的比值（RLT）与晶粒尺寸相关性的新实验结果。在零场环境（零场冷却，ZFC）中。合成磁铁矿样品的平均晶粒尺寸范围为0.15至100μm，几乎代表单畴（SD），伪单畴（PSD）和多畴（MD）磁态。随着平均晶粒尺寸的减小，RLT比值从0.58单调增加到1.12，接近PSD晶粒（0.15-5μm）的单位，而小于MD磁铁矿（12-100μm）的单位。观察到针状磁铁矿的RLT比为1.27，其特征接近于SD行为。这些观察结果表明，在〜0.15至〜5μm的范围内，低温SIRM可能高于“正常”磁畴壁位移所预期的温度。这些行为可能是由于这些晶粒的磁化过程中存在SD类成分而引起的，但是其来源尚不确定。含有接近化学计量磁铁矿的天然岩石表现出与合成磁铁矿相同的RLT比对磁畴状态的依赖性。因此，在非常低的温度下比较FC SIRM和ZFC SIRM可能可以粗略估算某些含磁铁矿的岩石中的磁畴状态，例如浅铁镁铁矿侵入物或某些海洋沉积物。

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