Effet de la vitesse de refroidissement sur l'intensité de l'aimantation thermorémanente: étude expérimentale, conséquences théoriques

Biquand, Daniel

doi:10.1139/e94-117

Cited by 14 publications

(14 citation statements)

References 18 publications

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“…This prediction has been experimentally confirmed by studies on archeological baked clay [Fox and Aitken, 1980] and on SD hematite [Papusoi, 1972a]. The same trend was confirmed for PSD size grains in baked clays, potsherds, and volcanic rocks [Yang et al, 1993;Biquand, 1994;Chauvin et al, 2000]. However, exactly the opposite trend was observed for MD magnetite [Papusoi, 1972b] (see also McClelland-Brown [1984]; Perrin [1998]) and remains unexplained.…”

Section: Af Demagnetization Of Arms With Different Acquisition Decay mentioning

confidence: 60%

Decay‐rate dependence of anhysteretic remanence: Fundamental origin and paleomagnetic applications

Dunlop

2003

J. Geophys. Res.

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[1] We have measured the intensity of anhysteretic remanent magnetization (ARM) as a function of alternating field (AF) decay rate. For synthetic and natural single-domain (SD) and pseudo-single-domain (PSD) magnetites, ARM intensity increases as decay rate decreases. Multidomain (MD) magnetites have the opposite response, ARM increasing as the decay rate increases. These are identical to the SD/PSD and MD dependences of thermoremanent magnetization on cooling rate. For all grain sizes and domain structures, ARM intensity increases as the AF decay rate used to achieve an initial demagnetized state decreases. Decay-rate differences in ARM intensity are a property of low-and medium-coercivity grains, as shown by annealing and by stepwise AF demagnetizing samples. We interpret the SD results to mean that increased AF exposure time permits a closer approach to equilibrium magnetization. An approximate thermal activation theory based on Néel [1949] and an exact theory by Egli and Lowrie [2002] predict 6-11% increases in ARM for an order of magnitude decrease in decay rate, in reasonable accord with the observed 12% increase for 0.065 mm SD grains. For MD grains, we hypothesize that increased exposure time (slower decay) permits more efficient self-demagnetization, reducing ARM. Low-coercivity grains experience the largest self-demagnetizing fields and therefore have the largest decay-rate response. Initial-state decay-rate response is attributed to longer exposure times leaving domain walls more strongly pinned in deeper potential wells (the net self-demagnetizing field is zero in the demagnetized state). Acquisition decay-rate, annealing, and initial-state responses of PSD grains are a blend of SD and MD responses. Because ARM is the most frequently used normalizer in relative paleointensity determination, it is important either to use a standard decay rate or else to remove the decay-rate dependence by demagnetizing the ARM to $30% of its initial value (ARM 0.3 ). A standard demagnetization level for the normalizing ARM is particularly important when comparing paleointensity records from different laboratories.

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Section: Af Demagnetization Of Arms With Different Acquisition Decay mentioning

confidence: 60%

Decay‐rate dependence of anhysteretic remanence: Fundamental origin and paleomagnetic applications

Dunlop

2003

J. Geophys. Res.

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“…In particular, both Papusoi [1972a] and Fox and Aitken [1980] found that the slowly cooled (∼10 −3 K/s) magnetization was 5%-14% larger than the rapidly cooled (∼1 K/s) magnetization. Nearly the same outcome was confirmed for pseudo-single-domain-(PSD-) sized grains in baked clays or potsherds and glasses in volcanic rocks [e.g., Yang et al, 1993;Biquand, 1994;Genevey and Gallet, 2002;Genevey et al, 2003;Morales et al, 2006aMorales et al, , 2006bFerk et al, 2010]. However, exactly the opposite trend of lower magnetization for slower cooling was observed for multidomain (MD) magnetite [Papusoi, 1972b;Brown, 1984;Perrin, 1998] and remains poorly understood.…”

Section: Thellier Modelingmentioning

confidence: 77%

Importance of cooling rate dependence of thermoremanence in paleointensity determination

2011

J. Geophys. Res.

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[1] The practical effect of cooling rate on the magnitude of thermal remanent magnetization (TRM) is experimentally tested, using both natural and synthetic magnetites. For synthetic and natural single-domain (SD) magnetites, TRM intensity increases as the cooling rate decreases because a longer exposure time for slower cooling offers more chances to achieve an equilibrium magnetization. Multidomain (MD) magnetites have the opposite response: TRM decreases as the cooling rate increases because slower cooling allows more time to achieve lower magnetization because of self-demagnetization. For pseudo-single-domain (PSD) magnetite, the effect of cooling rate on the remanence intensity appears to be insignificant, intermediate in behavior between SD and MD. For a SD, TRM differences are restricted to lower temperatures but diminish near the Curie point, strongly indicating a serious problem in a conventional treatment of cooling rate correction. On the practical side, merely applying TRM differences as a correction can overcorrect the true paleointensity. Another important significance of the present study is that a cooling rate difference alone can cause a slight nonlinearity in an Arai plot for a SD.

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“…This effect is predicted by Néel's theory [ Néel , 1955; see also Dodson and McClelland‐Brown , 1980; Halgedahl et al , 1980] for single domain grain assemblages. It was further studied for different types of domain grains and experimentally observed for both volcanic products and archeological artifacts [e.g., Fox and Aitken , 1980; Biquand , 1994; Chauvin et al , 2000; Leonhardt et al , 2006]. This cooling rate effect is due to the fact that the cooling of the samples in the laboratory is typically faster than the original cooling.…”

Section: Diversity Of the Experimental Methodsmentioning

confidence: 99%

ArcheoInt: An upgraded compilation of geomagnetic field intensity data for the past ten millennia and its application to the recovery of the past dipole moment

Genevey

Gallet

Constable

et al. 2008

Geochem Geophys Geosyst

188

251

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[1] This paper presents a compilation of intensity data covering the past 10 millennia (ArcheoInt). This compilation, which upgrades the one of Korte et al. (2005), contains 3648 data and incorporates additional intensity and directional data sets. A large majority of these data ($87%) were acquired on archeological artifacts, and the remaining $13% correspond to data obtained from volcanic products. The present compilation also includes important metadata for evaluating the intensity data quality and providing a foundation to guide improved selection criteria. We show that $50% of the data set fulfill reasonable reliability standards which take into account the anisotropic nature of most studied objects (potsherds), the stability of the magnetization, and the data dispersion. The temporal and geographical distributions of this sub-data set are similar to those of the main data set, with $72% of the data dated from the past three millennia and $76% obtained from western Eurasia. Approximately half of the selected intensity data are associated with at least an inclination value. To constrain the axial and full dipole evolution over the past three millennia requires that we avoid any overrepresentation of the western Eurasian data. We introduce a first-order regional weighting scheme based on the definition of eight widely distributed regions of 30°width within which the selected data are numerous enough. The regional curves of virtual axial dipole moments (VADM) and of mixed VADM-virtual dipole moments (VDM) averaged over sliding windows of 200 years and 500 years testify for strong contributions from either equatorial dipole or nondipole components. The computation of global VADM and mixed VADM/VDM variation curves, assuming an equal weight for each region, yields a dipole evolution marked by a distinct minimum around 0 B.C./A.D. followed by a maximum around the third-fourth century A.D. A second minimum is present around the eighth century A.D. This variation pattern is compatible with the one deduced from earlier, more sophisticated analysis based on the inversion of both intensity and directional data. In particular, there is a good agreement among all VADMs and dipole moment estimates over the historical period, which further strengthens the validity of our weighting scheme.

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Effet de la vitesse de refroidissement sur l'intensité de l'aimantation thermorémanente: étude expérimentale, conséquences théoriques

Cited by 14 publications

References 18 publications

Decay‐rate dependence of anhysteretic remanence: Fundamental origin and paleomagnetic applications

Decay‐rate dependence of anhysteretic remanence: Fundamental origin and paleomagnetic applications

Importance of cooling rate dependence of thermoremanence in paleointensity determination

ArcheoInt: An upgraded compilation of geomagnetic field intensity data for the past ten millennia and its application to the recovery of the past dipole moment

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