Partial anhysteretic remanent magnetization in magnetite 2. Reciprocity

Yu, Yongjae; Dunlop, David J.; Özdemir, Özden

doi:10.1029/2001jb001269

Cited by 14 publications

(13 citation statements)

References 25 publications

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“…The purpose of this paper and the companion paper by Yu et al [2002] (hereinafter referred to as paper 2) is to investigate systematically the additivity and reciprocity of pARMs. Experimental tests of the independence of pARMs will be reported elsewhere.…”

Section: Introductionmentioning

confidence: 99%

Partial anhysteretic remanent magnetization in magnetite 1. Additivity

Dunlop

Özdemir

2002

J. Geophys. Res.

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[1] We have tested the additivity of partial anhysteretic remanent magnetization (pARM) for suites of eight synthetic magnetites with mean grain sizes from 65 nm to 18 mm and 18 natural samples including lake sediments, oceanic and continental volcanic rocks, gabbros, and granites. In both synthetic and natural sample suites, domain states inferred from hysteresis and other magnetic properties vary from single-domain (SD) through pseudosingle-domain (PSD) to multidomain (MD). For each sample, total ARM intensity was compared with sums of partial ARMs of three different types: four conjugate pairs of parallel pARMs; four pairs of perpendicular pARMs; and one set of five neighboring parallel pARMs. In each case, the intervals of alternating field (AF) over which a steady field H was applied to produce the partial ARMs are nonoverlapping and cover the entire AF range (0-100 mT) used to produce the total ARM. Additivity of partial ARMs was verified to better than ±3% for all the samples, whatever the domain state (SD, PSD, and MD) or composition (ranging from pure magnetite to x = 0.6 titanomagnetite). The universality of pARM additivity is unexpected because its analog, partial thermoremanent magnetization (pTRM), deviates from ideal behavior as the grain size increases and the domain structure becomes MD. The different behaviors probably result from the fact that pARM is produced at ordinary temperatures over short times, whereas the most intense pTRM is produced at temperatures approaching the Curie point with significant dwell times, promoting such processes as isothermal remanence acquisition, domain nucleation, and domain wall reequilibration. Verification of the law of additivity of pARMs is an encouraging first step toward validating pseudo-Thellier and other methods of paleointensity determination that use ARM in place of, or in addition to, TRM.

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Section: Introductionmentioning

confidence: 99%

Partial anhysteretic remanent magnetization in magnetite 1. Additivity

Dunlop

Özdemir

2002

J. Geophys. Res.

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“…It is possible that ARM favors metastable configurations such as metastable SD states, while domain walls develop in pARM acquisition at higher AF. As argued by Yu et al [2002a], this interesting behavior seems to be one of the missing links in our complete understanding of paleointensity determination.…”

Section: Discussionmentioning

confidence: 87%

Effect of low‐temperature treatments on pseudo‐Thellier paleointensity determination

Dunlop

Özdemir

2003

J. Geophys. Res.

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[1] In paleointensity determination on multidomain (MD) magnetite, demagnetization is always easier than restoring remanence in companion acquisition steps. As a result, paleointensity results follow a convex-down curve on the Arai plot. In an attempt to overcome this problem, the effect of systematic low-temperature demagnetization (LTD) on pseudo-Thellier results was examined. LTD was applied not only to the initial anhysteretic remanent magnetization (ARM, simulating natural remanent magnetization or NRM) but also after each partial anhysteretic remanent magnetization (pARM) acquisition step. Three practical benefits of systematic LTD were discovered. (1)

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“…Yu et al (2002) have determined the size of this powder to be 65 ± 36 nm, with an axial ratio of 1.5 ± 0.4 (corresponding to a shape anisotropy factor N of about 0.13 (Stacey & Banerjee, 1974). Commercial magnetite powder by Wright Instruments, product number 4000, with a mean particle size of 50 nm was used.…”

Section: Interacting Magnetite Powder Samplementioning

confidence: 99%

Time‐Asymmetric FORC Diagrams: A New Protocol for Visualizing Thermal Fluctuations and Distinguishing Magnetic Mineral Mixtures

Berndt

Chang

Wang

et al. 2018

Geochem Geophys Geosyst

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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 a missing link between 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 field Ha for a longer time (minutes) than the FORC measurement field Hb (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.

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Partial anhysteretic remanent magnetization in magnetite 2. Reciprocity

Cited by 14 publications

References 25 publications

Partial anhysteretic remanent magnetization in magnetite 1. Additivity

Partial anhysteretic remanent magnetization in magnetite 1. Additivity

Effect of low‐temperature treatments on pseudo‐Thellier paleointensity determination

Time‐Asymmetric FORC Diagrams: A New Protocol for Visualizing Thermal Fluctuations and Distinguishing Magnetic Mineral Mixtures

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