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David J. Dunlop - One of the best experts on this subject based on the ideXlab platform.
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inverse Thermoremanent Magnetization
Journal of Geophysical Research, 2006Co-Authors: David J. DunlopAbstract:[1] Inverse Thermoremanent Magnetization (ITRM) is reversed to the Thermoremanent Magnetization (TRM) process: ITRM results from warming from low temperature T in a magnetic field, while TRM results from field cooling from high T. The development of ITRM was studied in magnetites of grain sizes from submicron to 135 μm, in pyrrhotites and in hematite crystals. All three minerals acquired ITRM after warming through their magnetic transitions (35 K for pyrrhotite, 120 and 130 K for magnetite, 250 K for hematite). However, when an impacting meteorite's cold interior warms to ambient T in the geomagnetic field, magnetite is the most likely candidate for acquiring ITRM. The magnetite ITRM blocking temperature distribution was determined from 12 neighboring partial ITRMs in nested field-on warming plus field-off cooling cycles (300–20 K). The largest partial ITRMs are produced in T intervals around magnetite's Verwey transition (TV = 110–120 K) and isotropic point (TK = 130 K). Both transitions involve large changes in crystalline anisotropy and renucleation of magnetic domains. ITRM is blocked when initially broad domain walls narrow and are pinned by dislocations. ITRM has contrasting properties to TRM, which is mainly due to blocked single-domain moments. ITRM is strongest for 3- to 20-μm grains, whereas TRM peaks for submicron magnetites. Only 10–20% of ITRM survives low-temperature deMagnetization (LTD) at 77 K or AF deMagnetization to 10–15 mT, compared to 30–90% for TRM. ITRM decreases quasi-linearly with T in thermal deMagnetization. The median unblocking temperature TUB is ≈300°C and 20–25% survives at 550°C. The low-TUB part of ITRM could mimic extraterrestrial NRM of low TUB, cited as evidence of negligible heating of meteorites in their transfer to Earth. The high-TUB ITRM would contaminate paleointensity determinations up to the highest T steps. The best cure for ITRM contamination is AF or LTD pretreatment.
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Thermoremanent Magnetization of multidomain hematite
Journal of Geophysical Research, 2005Co-Authors: Özden Özdemir, David J. DunlopAbstract:hematites. High-unblocking-temperature TRM and TRM memory must be due to magnetoelasti c pinning of spins in the basal plane by lattice defects, because both TRM and memory decrease with high-temperature treatment, which anneals out defects. The memory phenomenon seems to be in essence an amplification of residual magnetism that survives below the Morin transition. Remanence produced in a demagnetized sample below TM and room temperature remanence that has been cooled through TM increase in identical ways on warming through the transition. We propose that small regions of canted spins, pinned by crystal defects, remain below TM when the bulk of spins have aligned with the antiferromagnetic c axis. These nuclei serve to regenerate room temperature domain structure and remanence in warming through TM.
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on partial Thermoremanent Magnetization tail checks in thellier paleointensity determination
Journal of Geophysical Research, 2003Co-Authors: David J. DunlopAbstract:[1] Coarse magnetite grains, of multidomain (MD) or large pseudo-single-domain (PSD) size (≥10 μm approximately), cause nonlinearity and other problems in paleomagnetic field intensity determination and can lead to spurious paleointensity values. One suggested method of detecting their presence is to carry out an additional zero-field heating step following the acquisition of partial Thermoremanent Magnetization (pTRM) to check for complete deMagnetization of the pTRM. Residual undemagnetized pTRMs (“pTRM tails”) are characteristic of MD and large PSD grains and cause nonideal behavior in Thellier-type paleointensity experiments. We have measured pTRM tails in synthetic and natural magnetites of many sizes and domain states (including PSD and MD), starting from two different initial states. First, a thermally demagnetized sample was given a pTRM by cooling in a field H from the blocking temperature TB. The pTRM tail is the remanence ΔMptr remaining after zero-field reheating to TB. ΔMptr is most prominent for large grain sizes and when TB ≥ 500°C. We next measured pTRM tails ΔMptr* produced in a Thellier paleointensity experiment. The initial state in this case is a total Thermoremanent Magnetization gradually reduced by double heatings (zero-field followed by in-field) to a set of increasing TB. For all synthetic and natural samples containing large PSD and MD magnetites, regardless of grain size or lithologic differences, ΔMptr is significant but ΔMptr* is negligible. That is, the pTRM tail checks are always zero in our model Thellier experiments. However, in practical paleointensity studies, the pTRM tail check method has been shown to be successful in detecting MD grains. The reason for these contrasting results is that our experiments were carried out with the field Hlab that produced pTRM equal in intensity and parallel to the field H that produced natural remanent Magnetization (NRM). In this special situation the pTRM tail is completely masked. For the pTRM tail check method to be most effective, either Hlab should be applied at a large angle to the NRM direction or Hlab should be larger than (twice or more) the paleofield H. This will highlight the pTRM tail; in the first case by deflecting the apparent NRM direction after the tail-check step, and in the second case by increasing the apparent NRM intensity.
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partial Thermoremanent Magnetization louis neel s legacy in rock magnetism invited
Journal of Applied Physics, 2003Co-Authors: David J. DunlopAbstract:Louis Neel’s theories of Thermoremanent Magnetization (TRM) underlie all of rock magnetism. Neel’s relaxation time equation for thermal activation of single-domain (SD) moments has been verified over geological time and temperature scales by laboratory thermal deMagnetization of TRM overprints acquired in nature. For multidomain (MD) grains, disagreement with Neel’s predictions is explained by re-equilibration of domain walls by the changing internal demagnetizing field during heating. Much effort has been devoted to testing the laws of additivity, reciprocity, and independence of partial TRMs, which partition the blocking temperature range and appear in nature as successive overprints of the original TRM. For SD grains, the laws are explained by Neel’s theories and are verified experimentally. For MD grains, additivity holds but partial TRMs do not demagnetize over exactly the original blocking temperature interval (nonreciprocity) and are not entirely independent of one another when acquired in different directions. The current frontier in rock magnetism is to overcome this nonideal partial TRM behavior in order to extract precise and trustworthy records of ancient Earth’s magnetic field directions and intensities.
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Thermoremanent Magnetization of nonuniformly magnetized grains
Journal of Geophysical Research, 1998Co-Authors: David J. DunlopAbstract:A simple and elegant interpretation of Thermoremanent Magnetization (TRM) in uniformly magnetized single-domain (SD) grains was given by Neel 50 years ago, but the TRM acquisition processes in larger, nonuniformly magnetized grains are more varied and difficult to describe theoretically. SD TRM is a frozen high-temperature partition between two microstates: spins parallel or antiparallel to an applied magnetic field. Nonuniformly magnetized grains have a much greater choice of microstates (local energy minimum or LEM states), and partitioning among various LEM states continues to change during cooling. These changes may involve Barkhausen jumps of domain walls between positions of minimum local energy or nucleation of new domains and walls. Because of the lower remanence capacity of nonuniform microstates compared to the uniform SD state, TRM intensity decreases as grain size increases, although certain microstates, e.g., single-vortex states, seem to contribute little to TRM. Thermal deMagnetization of TRM begins just above room temperature and continues to the Curie point, quite unlike the sharp “unblocking” of SD TRM. This continuous deMagnetization, resulting from changes in microstates driven by the changing internal demagnetizing field during heating, profoundly affects the separation of different components of natural remanent Magnetization and the determination of paleomagnetic field intensity.
Marco Zannetti - One of the best experts on this subject based on the ideXlab platform.
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scaling of the linear response function from zero field cooled and Thermoremanent Magnetization in phase ordering kinetics
Physical Review E, 2003Co-Authors: Federico Corberi, Eugenio Lippiello, Marco ZannettiAbstract:In this paper we investigate the relation between the scaling properties of the linear response function R(t,s), of the Thermoremanent Magnetization (TRM) and of the zero field cooled Magnetization (ZFC) in the context of phase ordering kinetics. We explain why the retrival of the scaling properties of R(t,s) from those of TRM and ZFC is not trivial. Preasymptotic contributions generate a long crossover in TRM, while ZFC is affected by a dangerous irrelevant variable. Lack of understanding of both these points has generated some confusion in the literature. The full picture relating the exponents of all the quantities involved is explicitely illustrated in the framework of the large N model. Following this scheme, an assessment of the present status of numerical simulations for the Ising model can be made. We reach the conclusion that on the basis of the data available up to now, statements on the scaling properties of R(t,s) can be made from ZFC but not from TRM. From ZFC data for the Ising model with d = 2,3,4 we confirm the previously found linear dependence on dimensionality of the exponent a entering R(t,s) � s (1+a) f(t/s). We also find evidence that a recently derived form of the scaling function f(x), using local scale invariance arguments [M.Henkel,
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scaling of the linear response function from zero field cooled and Thermoremanent Magnetization in phase ordering kinetics
Physical Review E, 2003Co-Authors: Federico Corberi, Eugenio Lippiello, Marco ZannettiAbstract:In this paper we investigate the relation between the scaling properties of the linear response function $R(t,s),$ of the Thermoremanent Magnetization (TRM) and of the zero-field-cooled (ZFC) Magnetization in the context of phase-ordering kinetics. We explain why the retrieval of the scaling properties of $R(t,s)$ from those of TRM and ZFC Magnetization is not trivial. Preasymptotic contributions generate a long crossover in TRM, while ZFC Magnetization is affected by a dangerous irrelevant variable. Lack of understanding of both these points has generated some confusion in the literature. The full picture relating the exponents of all the quantities involved is explicitly illustrated in the framework of the large-$N$ model. Following this scheme, an assessment of the present status of numerical simulations for the Ising model can be made. We reach the conclusion that on the basis of the data available up to now, statements on the scaling properties of $R(t,s)$ can be made from ZFC Magnetization but not from TRM. From ZFC data for the Ising model with $d=2,3,4$ we confirm the previously found linear dependence on dimensionality of the exponent a entering $R(t,s)\ensuremath{\sim}{s}^{\ensuremath{-}(1+a)}f(t/s).$ We also find evidence that a recently derived form of the scaling function $f(x),$ using local scale invariance arguments [M. Henkel, M. Pleimling, C. Godr\`eche, and J. M. Luck, Phys. Rev. Lett. 87, 265701 (2001)], does not hold for the Ising model.
M Inoue - One of the best experts on this subject based on the ideXlab platform.
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time decay of Thermoremanent Magnetization and relaxation spectra in the cluster glass of itinerant magnetic fextis2
Journal of Magnetism and Magnetic Materials, 1998Co-Authors: H Negishi, M Sasaki, M Inoue, A Yamasaki, Hideoki KadomatsuAbstract:Abstract Time decays of the Thermoremanent Magnetization (TRM) in the cluster-glass (CG) phase of Fe x TiS 2 ( x= 1 3 , T g =53 K) have been measured using the anomalous Hall effect at three fixed temperatures 24.3, 29.3, and 34.3 K, over the time range 10 −1 –10 4 s with the cooling-fields H FC =0.005–0.14 T. For a low field-cooling ( H FC ⩽0.035 T), the Hall resistivity or TRM decays according to the power law ρ H ( t )= At − m in a short time range and the overall decay curves over the wide time range can be reproduced by an existing domain theory. By comparing the theory with experiments, we have obtained the equilibrium relaxation spectrum Q ( τ ) for x= 1 3 , which is much wider and smaller than those for another CG system ( x= 1 4 ) and a spin-glass one ( x =0.20). For a higher field-cooling ( H FC ⩾0.07 T), we have observed the unusual decay profiles that cannot be explained by the domain theory. For these dynamical properties of Fe 1/3 TiS 2 , we have made qualitative discussions by considering a random distribution of Fe atoms with up- and down-spins in the two-dimensional hexagonal layer of Fe x TiS 2 , where the formation and decomposition of some percolated cluster formed by the nearest and next-nearest interactions play an important role in the time decay profiles that depend on Fe concentration, cooling-field, and temperature.
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relaxation of Thermoremanent Magnetization in the spin glass phase of itinerant magnetic fextis2
Journal of Magnetism and Magnetic Materials, 1996Co-Authors: Y Hara, H Negishi, M Sasaki, M InoueAbstract:Abstract Time decays of the Thermoremanent Magnetization (TRM) in the spin-glass phase of Fe x TiS 2 ( x = 0.20, T g = 41 K) have been measured using the anomalous Hall effect over the time range 10 −2 –10 4 s with waiting time t w = 180–18000 s at temperatures T below T / T g ∼ 0.7. After the cooling field H FC (0.01–0.14 T) is switched off, the Hall resistivity (or TRM), within a short time span, follows a power law of the form ρ H ( t ) = At − m ( A is a constant), where the magnetic field and temperature-dependent exponent m are expressed in a universal form, m = Dξ γ , with the parameter of ‘relative relaxed Magnetization’ (RRM) ξ. The decay profiles over the wide time range are analyzed using the existing ‘domain theory’ with some modifications of the theoretical expressions. With the evaluated parameters, the equilibrium relaxation spectra, overlap lengths, and time-dependent maximum relaxation times that characterize the domain growth and the dynamical properties in this material are discussed.
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time decay of Thermoremanent Magnetization in cluster glass phase of intercalation compound fextis2 studied by use of anomalous hall effect
Journal of Magnetism and Magnetic Materials, 1995Co-Authors: Y Hara, H Negishi, M Sasaki, M Inoue, V A KulbachinskiiAbstract:Abstract Time decay of Hall resistivity ρ H after field-cooling under magnetic fields H FC = 0.035–0.14 T for a cluster-glass phase of Fe x TiS 2 ( x = 1 4 , T g = 53 K ) has been measured over the temperature range 4.2–35 K and time range 10 −1 –10 3 s. After the magnetic field is switched off to zero at time t = 0, the Hall voltage decays with time obeying the power law ρ H ( t ) = At − m in a short time range up to t d , beyond which the decay becomes faster than a power law. The temperature and magnetic field dependences of the exponents m are analyzed to obtain a universal relation for the Thermoremanent Magnetization (TRM), m = Dξ , where ξ is a characteristic quantity, defined by ξ = 1 − M (0)/ M FC ( T → 0); M FC ( T → 0) is the Magnetization at H = H FC extrapolated to T = 0 and M (0) the remanent Magnetization at time t = 0. Comparison with the present field-cooled and the zero-field case (isothermal remanent Magnetization, IRM) is made to emphasize the dependence of relaxation behavior on the magnetic history.
Mark J Dekkers - One of the best experts on this subject based on the ideXlab platform.
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the effect of cooling rate on the intensity of Thermoremanent Magnetization trm acquired by assemblages of pseudo single domain multidomain and interacting single domain grains
Geophysical Journal International, 2013Co-Authors: Andrew J Biggin, S Badejo, Emma Hodgson, Adrian R Muxworthy, John Shaw, Mark J DekkersAbstract:SUMMARY Experiments designed to measure the absolute palaeointensity of the geomagnetic field generally do so by comparing the ancient Thermoremanent Magnetization (TRM) retained by an igneous rock with a new TRM imparted in the laboratory. One problem with this procedure is that the relative magnitudes of the ancient and laboratory TRMs may be influenced, not only by the external field intensities at the time the two coolings took place, but also by the rate at which the coolings themselves occurred. Here, we present new measurements of this ‘cooling rate effect’ obtained from treatments in the laboratory differing in cooling rate by a factor of ∼200. Synthetic samples containing sized ferrimagnetic grains were used in the experiments. Theoretical considerations and previous experiments have indicated the cooling rate effect to be dependent on domain state. Increases in TRM magnitude of more than 7percent per order of magnitude decrease in cooling rate have been reported for assemblages of non-interacting single-domain (SD) grains. Here, we focus on magnetite grains in the less well-studied pseudo-single domain (PSD) and multidomain (MD) states using a range of applied field intensities to impart the TRMs. For the first time, we also measure the cooling rate effect in grains of titanomagnetite that have been oxyexsolved so that they contain strongly interacting SD lamellae. In all cases, the cooling rate effect measured was in the same sense as alreadyobservedinidealmagneticallynon-interactingSDgrainsbutwasconsiderablyweaker. On average, the effect did not exceed ∼3percent increase in TRM per order of magnitude decrease in cooling rate and did not show any systematic dependence on appliedfield intensity. Insomesamples containing coarsergrains,thecoolingrateeffectwasnotdistinguishablefrom zero. The sense and magnitude of the cooling rate effect remain uncertain in truly MD grains as different studies have produced discrepant results. For the more practically relevant case of PSD and interacting SD grains, which commonly dominate the TRM in igneous rocks, however, it appears that we can be more confident in our assertions. The cooling rate effect in such materials is in the same sense as in non-interacting SD grains but smaller: a consequence of long-range ordering. In lavas and small intrusions containing these, it is unlikely to exceed 10percent. Although a correction should always be attempted, the results of palaeointensity studies based upon such samples will generally not be severely biased.
Federico Corberi - One of the best experts on this subject based on the ideXlab platform.
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scaling of the linear response function from zero field cooled and Thermoremanent Magnetization in phase ordering kinetics
Physical Review E, 2003Co-Authors: Federico Corberi, Eugenio Lippiello, Marco ZannettiAbstract:In this paper we investigate the relation between the scaling properties of the linear response function R(t,s), of the Thermoremanent Magnetization (TRM) and of the zero field cooled Magnetization (ZFC) in the context of phase ordering kinetics. We explain why the retrival of the scaling properties of R(t,s) from those of TRM and ZFC is not trivial. Preasymptotic contributions generate a long crossover in TRM, while ZFC is affected by a dangerous irrelevant variable. Lack of understanding of both these points has generated some confusion in the literature. The full picture relating the exponents of all the quantities involved is explicitely illustrated in the framework of the large N model. Following this scheme, an assessment of the present status of numerical simulations for the Ising model can be made. We reach the conclusion that on the basis of the data available up to now, statements on the scaling properties of R(t,s) can be made from ZFC but not from TRM. From ZFC data for the Ising model with d = 2,3,4 we confirm the previously found linear dependence on dimensionality of the exponent a entering R(t,s) � s (1+a) f(t/s). We also find evidence that a recently derived form of the scaling function f(x), using local scale invariance arguments [M.Henkel,
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scaling of the linear response function from zero field cooled and Thermoremanent Magnetization in phase ordering kinetics
Physical Review E, 2003Co-Authors: Federico Corberi, Eugenio Lippiello, Marco ZannettiAbstract:In this paper we investigate the relation between the scaling properties of the linear response function $R(t,s),$ of the Thermoremanent Magnetization (TRM) and of the zero-field-cooled (ZFC) Magnetization in the context of phase-ordering kinetics. We explain why the retrieval of the scaling properties of $R(t,s)$ from those of TRM and ZFC Magnetization is not trivial. Preasymptotic contributions generate a long crossover in TRM, while ZFC Magnetization is affected by a dangerous irrelevant variable. Lack of understanding of both these points has generated some confusion in the literature. The full picture relating the exponents of all the quantities involved is explicitly illustrated in the framework of the large-$N$ model. Following this scheme, an assessment of the present status of numerical simulations for the Ising model can be made. We reach the conclusion that on the basis of the data available up to now, statements on the scaling properties of $R(t,s)$ can be made from ZFC Magnetization but not from TRM. From ZFC data for the Ising model with $d=2,3,4$ we confirm the previously found linear dependence on dimensionality of the exponent a entering $R(t,s)\ensuremath{\sim}{s}^{\ensuremath{-}(1+a)}f(t/s).$ We also find evidence that a recently derived form of the scaling function $f(x),$ using local scale invariance arguments [M. Henkel, M. Pleimling, C. Godr\`eche, and J. M. Luck, Phys. Rev. Lett. 87, 265701 (2001)], does not hold for the Ising model.
