109 research outputs found
Low-temperature magnetism of alabandite : Crucial role of surface oxidation
Manganese(II) monosulphide crystallizes into three different polymorphs (alpha-, beta-, and gamma-MnS). Out of these, alpha-MnS, also known as mineral alabandite, is considered the most stable and is widespread in terrestrial materials as well as in extraterrestrial objects such as meteorites. In this study, a low-temperature antiferromagnetic state of alpha-MnS was investigated using macroscopic magnetic measurements as induced and remanent field-cooled (FC) and zero-field-cooled (ZFC) magnetizations and magnetic hysteresis. Both natural alabandite and synthetic samples show (i) NĂ©el temperatures in a narrow temperature range around 153 K and (ii) a rapid increase of the magnetization around 40 K. An anomalous magnetic behavior taking place at about 40 K was previously ascribed to the magnetic transition from a high-temperature antiferromagnetic to a low-temperature ferromagnetic state documented for non-stoichiometric alpha-MnS slightly enriched in manganese. However, our detailed microscopic observations and, in particular, oxidation experiments indicate that the anomalous magnetic behavior around 40 K is caused by a presence of oxide layer of ferrimagnetic hausmannite (Mn3O4) on the surface of alpha-MnS rather than being an intrinsic property of nearly stoichiometric alpha-MnS.Peer reviewe
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Method of Equivalencing for a Large Wind Power Plant with Multiple Turbine Representation: Preprint
This paper focuses on our effort to develop an equivalent representation of a Wind Power Plant collector system for power system planning studies
Magnetism and mineralogy of Almahata Sitta polymict ureilite (= asteroid 2008 TC 3): Implications for the ureilite parent body magnetic field
The Almahata Sitta meteorite is the first case of recovered extraterrestrial material originating from an asteroid that was detected in near Earth space shortly before entering and exploding in the high atmosphere. The aims of our project within the 2008 TC 3 consortium were investigating Almahata Sittaâs (AS) magnetic signature, phase composition and mineralogy, focussing on the opaque minerals, and gaining new insights into the magnetism of the ureilite parent body (UPB). We report on the general magnetic properties and behavior of Almahata Sitta and try to place the results in context with the existing data set on ureilites and ureilite parent body models. The magnetic signature of AS is dominated by a set of low-Ni kamacites with large grain sizes. Additional contributions come from micron-sized kamacites, suessite, (Cr) troilite, and daubreelite, mainly found in the olivine grains adjacent to carbon-rich veins. Our results show that the paleomagnetic signal is of extraterrestrial origin as can be seen by comparing with laboratory produced magnetic records (IRM). Four types of kamacite (I-IV) have been recognized in the sample. The elemental composition of the ureilite vein metal Kamacite I (particularly Co) clearly differs from the other kamacites (II-IV), which are considered to be indigenous. Element ratios of kamacite I indicate that it was introduced into the UPB by an impactor, supporting the conclusions of Gabriel and Pack (2009)
Magnetic particle characterization in the Seine river system: Implications for the determination of natural versus anthropogenic input
International audience[1] This study presents an innovative application of well-established environmental magnetic proxy parameters on fluvial sediments, with the aim to trace geological and human-induced processes in the complex Seine river drainage system in northern France. We seek to identify environmental fingerprints of mechanical and chemical weathering processes, the regional distribution of the suspended material, and changes in the balance of natural input versus anthropogenic pollution. In order to reach these goals, we applied a combination of rock magnetic and advanced scanning electron microscopic techniques on a large number of sediment trap samples. Generally, we observe an increase in magnetic concentration coupled with a coarsening in magnetic grain size downstream of the Seine river system. Furthermore, the dominant magnetomineralogy changes from high-coercivity minerals upstream in more rural areas to magnetite-dominated assemblages downstream. Each river (segment) shows its specific trend line depending on regional initial input, weathering conditions, drainage area, and potential pollution sources. One major outcome of this study is the observed significant correlation between anthropogenic antimony-rich iron oxide particles and the magnetic concentration. This shows the potential of magnetic remanence measurements as proxy parameters for specific heavy metal pollution concentrations. Hence, the environmental magnetic study presented herein serves to identify major trends as well as local particularities and leads to quantitative analyses of the contributions of individual tributaries in the Seine river system. Components: 9513 words, 9 figures, 4 tables
New archaeointensity data from Italy and geomagnetic ïŹeld intensity variation in the Italian Peninsula
We present new archaeointensity results from three Italian kilns situated at Ascoli Satriano,
Vagnari and Fontanetto Po obtained with the Thellier modified by Coe double heating method.
These data complement the directional results previously published. All sites are dated on
the basis of archaeological information and/or thermoluminescence dating. The results are
corrected for the anisotropy of the thermoremanent magnetization and the cooling rate effects.
The new data are compared with previously published archaeointensity data from Italy and
nearby countries within 900 km radius from Viterbo. An initial data set including archaeointesity
data mainly coming from Italy, France, Switzerland, Czech Republic, Slovakia, Hungary,
Greece and Bulgaria has been compiled. After the application of strict selection criteria, the
most reliable data have been used for the calculation of a preliminary Italian intensity secular
variation (SV) curve for the last 3000 yr. The new curve covers the 300 BCâ400 AD
and 1200â1900 AD periods. It is established by means of sliding windows of 200 yr shifted
by 100 yr. The lack of reliable data for the 1000â200 BC and 400â1200 AD time intervals
does not permit the calculation of a continuous curve. Clearly, more high-quality archaeointensity
data from Italy and Europe are still needed to draw a robust intensity SV curve for
the Italian Peninsula that could be used for archaeomagnetic dating in combination with the directional data
Domain wall pinning and dislocations: Investigating magnetite deformed under conditions analogous to nature using transmission electron microscopy
In this study, we deformed samples cut from a single magnetite octahedron and used transmission electron microscopy (TEM) and magnetic measurements to experimentally verify earlier computational models of magnetic domain wall pinning by dislocations and to better understand the nature of dislocations in magnetite. Dislocations in magnetite have been of interest for many decades because they are often cited as a likely source of stable thermoremanent magnetizations in larger multidomain (MD) magnetite grains, so a better understanding of dislocation effects on coercivity in MD magnetite is crucial. TEM imaging shows, for the first time, domain walls sweeping through the magnetite sample and being pinned at dislocations. In agreement with theory, these findings demonstrate that domain walls are more strongly pinned at networks of dislocations than at single dislocations and that domain walls pinned at longer dislocations have higher microcoercivities than those pinned at shorter dislocations. This experimentally illustrates the ability of dislocations to increase the coercivity of larger multidomain magnetite grains. The observed values for microcoercivity and bulk coercivity are in reasonable agreement with theoretical calculations. Burgers vectors were determined for some dislocations to verify that they were in keeping with expected dislocation orientations. The dislocations were found to be primarily located on close-packed {111} planes within the magnetite. Deformation caused only a minor change in bulk coercivity, but first-order reversal curve diagrams show populations with increased coercivity not visible in hysteresis loops.The research leading to these
results has received funding from the
European Research Council under
the European Unionâs Seventh Framework
Programme (FP/2007-2013)/ERC
grant agreement 320750. The Institute
for Rock Magnetism and LacCore
are supported by the NSF EAR Instrumentation
and Facilities Program and
by the University of Minnesota, Earth
Sciences Division, National Science
Foundation. To obtain the data used
for this paper, please contact A.K.L.
This work was funded by EAR-0810085
to J.M.F., by EAR-0810252 to A.J.N., and
by a Geological Society of America
grant to A.K.L. This is IRM publication
1406.This is the final published version. It first appeared at http://onlinelibrary.wiley.com/doi/10.1002/2014JB011335/abstract?rememberMePresent=false
A comparison of Thellier-type and multispecimen paleointensity determinations on Pleistocene and historical lava flows from Lanzarote (Canary Islands, Spain)
Sixteen Miocene, Pleistocene, and historic lava flows have been sampled in Lanzarote (Canary
Islands) for paleointensity analysis with both the Coe and multispecimen methods. Besides obtaining new
data, the main goal of the study was the comparison of paleointensity results determined with two different
techniques. Characteristic Remanent Magnetization (ChRM) directions were obtained in 15 flows, and
12 were chosen for paleointensity determination. In Thellier-type experiments, a selection of reliable
paleointensity determinations (43 of 78 studied samples) was performed using sets of criteria of different
stringency, trying to relate the quality of results to the strictness of the chosen criteria. Uncorrected and
fraction and domain-state corrected multispecimen paleointensity results were obtained in all flows. Results
with the Coe method on historical flows either agree with the expected values or show moderately lower
ones, but multispecimen determinations display a large deviation from the expected result in one case. No
relation can be detected between correct or anomalous results and paleointensity determination quality or
rock-magnetic properties. However, results on historical flows suggest that agreement between both
methods could be a good indicator of correct determinations. Comparison of results obtained with both
methods on seven Pleistocene flows yields an excellent agreement in four and disagreements in three
cases. Pleistocene determinations were only accepted if either results from both methods agreed or a result
was based on a sufficiently large number (n>4) of individual Thellier-type determinations. In most
Pleistocene flows, a VADM around 5 31022 Am2 was observed, although two flows displayed higher values
around 931022 Am2.project
CGL2012-32149 (Ministerio de
Econom ıa y Competitividad, Spain),
project 320/2011 (Ministerio de Medio
Ambiente y Medio Rural y Marino,
Spain) and the European Regional
Development Fund (ERDF)
Full-vector archaeomagnetic dating of a medieval limekiln at Pinilla Del Valle site (Madrid, Spain)
Archaeomagnetic dating based on the full geomagnetic field vector was carried out on a limekiln excavated at Pinilla del Valle archaeological site (Madrid, Spain). The limekiln tradition in this area is largely documented by historical sources for recent centuries but the date of the studied kiln's last use was unknown. The combination of mean archaeomagnetic directional and absolute archaeointensity results shows that the kiln was last used between ad 1296 and 1413, in good agreement with two independent radiocarbon dates. This study provides the first archaeomagnetic evidence that the local limekiln tradition dates back to at least late medieval times. Furthermore, the inclusion of these data in the Iberian secular variation curve and geomagnetic field models will help to improve the archaeomagnetic dating technique.Spanish Ministry of Economy and Competitiveness, MINECO
and the European Regional Development Fund (projects CGL2012-38481 and CGL2012-32149).
AGacknowledges partial financial support given by PAPIIT IN-105214
Malleable Curie Temperatures of Natural Titanomagnetites: Occurrences, Modes, and Mechanisms
Abstract Intermediate-composition titanomagnetites have Curie temperatures (Tc) that depend not only on composition but also on thermal history, with increases of 100°C or more in Tc produced by moderate-temperature (300â400°C) annealing in the laboratory or in slow natural cooling and comparable decreases produced by more rapid cooling (âquenchingâ) from higher temperatures. New samples spanning a range of titanomagnetite compositions exhibit reversible changes in Tc comparable to those previously documented for pyroclastic samples from Mt. St. Helens and Novarupta. Additional high- and low-temperature measurements help to shed light on the nanoscale mechanisms responsible for the observed changes in Tc. High-T hysteresis measurements exhibit a peak in high-field slope khf(T) at the Curie temperature, and the peak magnitude decreases as Tc increases with annealing. Sharp changes in low-T magnetic behavior are also strongly affected by prior annealing or quenching, suggesting that these treatments affect the intrasite cation distributions. We have examined the effects of oxidation state and nonstoichiometry on the magnitude of Tc changes produced by quenching/annealing in different atmospheres. Treatments in air generally cause large changes (ÎTc \u3e 100°). In an inert atmosphere, the changes are similar in many samples but strongly diminished in others. When the samples are embedded in a reducing material, ÎTc becomes insignificant. These results strongly suggest that cation vacancies play an essential role in the cation rearrangements responsible for the observed changes in Tc. Some form of octahedral-site chemical clustering or short-range ordering appears to be the best way to explain the large observed changes in Tc
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