Magnetic Hysteresis Properties of Magnetite: Trends With Particle Size and Shape

IF 2.9 2区 地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS
Greig A. Paterson, Roberto Moreno, Adrian R. Muxworthy, Lesleis Nagy, Wyn Williams, Lisa Tauxe
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Abstract

Magnetic hysteresis measurements are routinely made in the Earth and planetary sciences to identify geologically meaningful magnetic recorders, and to study variations in present and past environments. Interpreting magnetic hysteresis data in terms of domain state and paleomagnetic stability are major motivations behind undertaking these measurements, but the interpretations remain fraught with challenges and ambiguities. To shed new light on these ambiguities, we have undertaken a systematic micromagnetic study to quantify the magnetic hysteresis behavior of room-temperature magnetite as a function of particle size (45–195 nm; equivalent spherical volume diameter) and shape (oblate, prolate and equant); our models span uniformly magnetized single domain (SD) to non-uniformly magnetized single vortex (SV) states. Within our models the reduced magnetization associated with SV particles marks a clear boundary between SD (≥0.5) and SV (<0.5) magnetite. We further identify particle sizes and shapes with unexpectedly low coercivity and coercivity of remanence. These low coercivity regions correspond to magnetite particles that typically have multiple possible magnetic domain state configurations, which have been previously linked to a zone of unstable magnetic recorders. Of all the hysteresis parameters investigated, transient hysteresis is most sensitive to particles that exhibit such domain state multiplicity. When experimental transient hysteresis is compared to paleointensity behavior, we show that increasing transience corresponds to more curved Arai plots and less accurate paleointensity results. We therefore strongly suggest that transient behavior should be more routinely measured during rock magnetic investigations.

Abstract Image

磁铁矿的磁滞特性:颗粒大小和形状的变化趋势
磁滞测量是地球和行星科学中的例行工作,目的是确定具有地质意义的磁记录器,并研究现在和过去环境的变化。从磁畴状态和古地磁稳定性的角度解释磁滞数据是进行这些测量的主要动机,但解释工作仍然充满挑战和不确定性。为了揭示这些模糊之处,我们开展了一项系统的微磁研究,以量化室温磁铁矿的磁滞行为与颗粒大小(45-195 nm;等效球形体积直径)和形状(扁球形、长球形和等球形)的函数关系;我们的模型涵盖了均匀磁化的单磁畴(SD)和非均匀磁化的单涡旋(SV)状态。在我们的模型中,与 SV 粒子相关的磁化降低标志着 SD(≥0.5)和 SV(<0.5)磁铁矿之间的明显界限。我们进一步确定了具有意外低矫顽力和剩磁矫顽力的颗粒尺寸和形状。这些低矫顽力区域与通常具有多种可能磁畴态配置的磁铁矿颗粒相对应,而这些磁畴态配置以前曾与不稳定磁记录器区域相关联。在所研究的所有磁滞参数中,瞬态磁滞对表现出这种磁畴状态多重性的颗粒最为敏感。当实验瞬态磁滞与古强度行为进行比较时,我们发现瞬态磁滞的增加对应于更弯曲的 Arai 图和更不准确的古强度结果。因此,我们强烈建议在岩石磁性研究中更多地测量瞬态行为。
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来源期刊
Geochemistry Geophysics Geosystems
Geochemistry Geophysics Geosystems 地学-地球化学与地球物理
CiteScore
5.90
自引率
11.40%
发文量
252
审稿时长
1 months
期刊介绍: Geochemistry, Geophysics, Geosystems (G3) publishes research papers on Earth and planetary processes with a focus on understanding the Earth as a system. Observational, experimental, and theoretical investigations of the solid Earth, hydrosphere, atmosphere, biosphere, and solar system at all spatial and temporal scales are welcome. Articles should be of broad interest, and interdisciplinary approaches are encouraged. Areas of interest for this peer-reviewed journal include, but are not limited to: The physics and chemistry of the Earth, including its structure, composition, physical properties, dynamics, and evolution Principles and applications of geochemical proxies to studies of Earth history The physical properties, composition, and temporal evolution of the Earth''s major reservoirs and the coupling between them The dynamics of geochemical and biogeochemical cycles at all spatial and temporal scales Physical and cosmochemical constraints on the composition, origin, and evolution of the Earth and other terrestrial planets The chemistry and physics of solar system materials that are relevant to the formation, evolution, and current state of the Earth and the planets Advances in modeling, observation, and experimentation that are of widespread interest in the geosciences.
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