High-temperature Susceptibility Research Articles

Paleolatitudinal movements of the eastern Sakarya Zone from Jurassic to Eocene

The study area covers a region oriented north-south from the Black Sea coastline in the north to the Kelkit Basin in the south within the eastern Sakarya Zone in northern Türkiye. The objective of this study is to investigate the paleolatitudinal movements of the eastern Sakarya Zone during the Jurassic-Eocene time interval through paleomagnetism. Various volcanic and sedimentary units (e.g., the Şenköy, Berdiga, Mescitli, Çatak, Kızılkaya, and Çağlayan Formations) spanning the time interval from the Early Jurassic to Middle Eocene were identified. A total of 98 locations belonging to Early/Middle Jurassic to Eocene volcanic and sedimentary units were selected for paleomagnetic core sample collection. The samples were subjected to demagnetization through thermal and alternating field methods. Characteristic remanent magnetization directions (ChRM) were obtained. Isothermal remanent magnetization (IRM) and high temperature susceptibility (HTS) measurements were made to identify the minerals responsible for magnetization. To ascertain whether magnetization was acquired through rock formation or as a consequence of subsequent tectonic processes, conglomerate and fold tests were performed. The results showed that magnetization was acquired before folding, i.e., the rocks have primary magnetization. Polarity tests were also conducted using coeval normal and reverse polarity sites. The results indicate that the mean magnetization direction for the Early-Middle Jurassic is 18.1°/55.2° (D/I) and 3.3°/51.5° (D/I) for sedimentary and volcanic rocks, respectively, and 348.7°/46.7° (D/I) for Late Jurassic/Early Cretaceous sedimentary rocks. In the Late Cretaceous period, the mean magnetization direction is 8.0°/49.3° (D/I) and 9.1°/47.0° (D/I) for sedimentary and volcanic rocks, respectively. In the case of the Early/Middle Eocene, the mean magnetization direction is 348.6°/52.7° (D/I) and 5.9°/48.8° (D/I) for sedimentary and volcanic rocks, respectively. In this study, the E/I correction was applied to the Late Jurassic/Early Cretaceous sedimentary rocks, and paleolatitude data obtained from sedimentary rocks were also utilized. Our paleomagnetic results indicate that the eastern Sakarya Zone was situated at latitudes spanning from 27.9° to 35.7° during the Early Jurassic - Middle Eocene time interval. In consequence, the eastern Sakarya Zone constituted a portion of the southern margin of the Eurasian continent during the Late Jurassic and Middle Eocene periods.

Comparative study on the magnetic properties of Fe-substituted Co2Sn1−x Fe x O4 spinel oxides and its exchange bias effect

Herein, we report the Fe-substituted Co2Sn1−x Fe x O4 (0 ⩽ x ⩽ 0.4) inverse spinel’s oxide using the solid-state reaction method. X-ray reveals the single-phase cubic structure with space group Fd3m. With increasing Fe in Co2Sn1−x Fe x O4 spinel oxide, the transition temperature rise. The ac susceptibility at different frequencies also confirms a spin-glassy state at lower temperatures. The strong exchange bias effect appears in the sample having Fe substitution (x = 0.2) under the presence of constant temperature ∼10 K. The high-temperature susceptibility of Curie-Wise fitting shows that the system changes from antiferromagnetic exchange (x < 0.2) to ferromagnetic exchange (x > 0.2).

Coal gangue in asphalt pavement: A review of applications and performance influence

The comprehensive utilization of coal gangue is low, and this causes serious environment problems and security risks. The physical and chemical properties of coal gangue were analyzed in this paper, and the estimated value of different chemical components of coal gangue was counted. The physical properties of coal gangue aggregate were analyzed, and performance and its influencing factors of base course mixture with coal gangue aggregate were studied. The influence of coal gangue powder and coal gangue aggregate on performance of asphalt mortar and asphalt mixture was analyzed, and possible influencing factors and function mechanism were discussed. The results showed that heavy metal elements of coal gangue applied into asphalt pavement is not seeped out. The crushing value, water absorption and flat elongated particles content of coal gangue aggregate are generally high, but the compressive strength of base course with coal gangue aggregate is verified to meet the strength requirement. The performance, volume stability and durability of base course with coal gangue aggregate are closely related to aggregate gradation, the type and dosage of cementations materials and aggregate. The high temperature performance, temperature susceptibility and viscosity of asphalt mortar are improved by the addition of different coal gangue powder, and improvement effect of activated coal gangue powder on asphalt mortar performance is better. The low temperature performance and adhesion property of asphalt mortar with chemical activated coal gangue powder are improved. The physical reaction between asphalt and different coal gangue powder is only taken place. The temperature stability of asphalt mixture with coal gangue coarse aggregate has achieved the specification requirement. The water stability and low temperature fracture performance of asphalt mixture with fine aggregate replaced by coal gangue are improved. However, the high temperature performance of above mixture is lower than conventional hot mix asphalt mixture. The research results will provide reference for coal gangue applied into asphalt pavement.

Association Analysis in Rice Germplasm Lines for High Temperature Tolerance

Background: Relative to other abiotic factors like salinity and drought, breeding rice cultivars that are resistant of high temperatures has received a little attention. The purpose of this study is to find parents and genotypes that are suitable for utilizing in high temperature stress breeding program. Methods: The genetic material for this study comprised of a set of germplasm collections (293 accessions) from different sources such as International Rice Research Institute germplasm. These populations were raised at the Department of Rice, Centre for Plant Breeding and Genetics, Tamil Nadu Agricultural University, Coimbatore. The Heat tolarance Indices (TOL) viz., Heat tolerance index (HTI) and Heat susceptibility index (HSI) and association analysis were estimated among germplasm lines for yield attributes under normal and high temperature stress condition. Result: Out of 293 genotypes, sixty nine genotypes significantly exceeded for both HTI and HSI. Association studies revealed that, single plant yield had highly significant and positive association with panicle exertion, number of total tillers per plant, number of productive tillers per plant, panicle length, number of filled grains per panicle and total dry matter production. Spikelet sterility and high temperature susceptibility index had highly significant and negative association with single plant yield. Number of productive tillers had significant and positive correlation with total dry matter production, panicle length, number of filled grains per panicle, days to maturity, hundred grain weight, grain breadth and high temperature susceptible index. Hence these traits may be considered as selection indices for yield and high temperature tolerance improvement programme. Hence it may be possible to combine single plant yield and heat susceptibility index by specific breeding programme for high temperature tolerance in rice.

Identification of magnetic mineralogy and paleo-flow direction of the Miocene-quaternary volcanic products in the north of Lake Van, Eastern Turkey

Abstract One of the major challenges facing geochemistry, petrology, and volcanology researchers is the difficulty in determining the origin and paleo-flow directions of igneous and volcanic rocks. It is not possible to clearly determine origins and paleo-flow directions in areas with numerous volcanic centers. Anisotropy of magnetic susceptibility (AMS) is a valuable method that provides insights into the origins and paleo-flow directions of lavas that are complex to study. The presence of volcanic materials with thicknesses up to 1 km, coming from different sources at varied time intervals in the north of Lake Van, makes this area an ideal setting for implementing AMS in establishing paleo-flow directions. This study presents the magnetic mineralogy and AMS analysis of volcanic rocks from the Miocene to the Quaternary in the Lake Van region. We conducted isothermal remanent magnetization (IRM) and high-temperature susceptibility (HTS) studies to determine the magnetic mineralogy. IRM studies revealed that (titano)magnetite is responsible for the magnetization in most samples, while both (titano)magnetite and hematite are responsible for the rest. Alteration degrees and Curie temperatures of the rock samples were also determined through HTS measurements. There is good agreement between the anticipated directions of lava flow and our findings for nearly all volcanic rocks.

New paleomagnetic results from Neogene to Quaternary volcanic rocks of north of the Lake Van, Eastern Turkey

The Eastern Anatolia is an active tectonic region where the collision between the Arabian and Eurasian plates take place. Due to the subduction of Arabian plate’s oceanic lithosphere under Eurasian plate, widespread volcanism observed in large areas began in Serravallian. There is no consensus in the literature for the tectonic evolution of the region. Therefore, there are many geological and geophysical studies conducted with the intention of explaining the tectonic evolution of Eastern Anatolia by geodynamic models. Our paleomagnetism study aims to reveal the tectonic rotations in order to better understand the development of the prevailing tectonism in the region from the volcanic rocks. Paleomagnetic samples were collected from 86 sites of the Late Miocene–Pleistocene volcanic rocks located at the north of Lake Van. Isothermal remanent magnetization studies show that magnetite is the mineral responsible for magnetization in most rocks, while both magnetite and hematite are responsible for the rest of the rocks. Curie temperatures and alteration degrees of rock samples were also determined by high-temperature susceptibility (HTS) studies. In some samples, titanomagnetite component was observed in the heating phase of the HTS measurements. The absence of this component in the cooling step indicates that Ti-magnetite is transformed into magnetite by alteration. The Pleistocene volcanics show counterclockwise rotation of R ± ΔR = 13.4° ± 3.8°. The Pliocene volcanic rocks were defined in four different groups: south of Erciş Fault, north of Erciş Fault, around Muradiye and north of Van. Also, the remarkable clockwise rotation is observed in the north of Van and near Muradiye R ± ΔR = 24.4° ± 17.0° and R ± ΔR = 6.9° ± 9.4°, respectively. In addition, counterclockwise rotation (R ± ΔR = 14.5° ± 6.1°) is obtained in the southern part of the Erciş Fault, while there is no significant rotation (R ± ΔR = 0.6° ± 7.4°) on the northern side. Late Miocene volcanic rocks show no significant rotation either (R ± ΔR = 1.8° ± 13.7°). Our new paleomagnetic results indicate that the left-lateral strike-slip Çakırbey Fault, located to the east of the Erciş fault and extending roughly in the northeast–southwest direction, may be active.

Interpreting high-temperature magnetic susceptibility data of natural systems

High-temperature susceptibility (HT-χ) data are routinely measured in Earth, planetary, and environmental sciences to rapidly identify the magnetic mineralogy of natural systems. The interpretation of such data can be complicated. Whilst some minerals are relatively unaltered by heating and are easy to identify through their Curie or Néel temperature, other common magnetic phases, e.g., iron sulphides, are very unstable to heating. This makes HT-χinterpretation challenging, especially in multi-mineralogical samples. Here, we report a review of the HT-χdata measured primarily at Imperial College London of common magnetic minerals found in natural samples. We show examples of “near pure” natural samples, in addition to examples of interpretation of multi-phase HT-χdata. We hope that this paper will act be the first reference paper for HT-χdata interpretation.

Van Vleck paramagnetism and enhancement of effective moment with magnetic field in rare earth orthovanadate EuVO4

The 4f6 systems were hypothesized to possess non-magnetic (J=0) ground state. However, all such systems have distinctly shown the presence of non-zero effective moment at low temperatures. In this context, a rare earth orthovanadate EuVO4, which in spite of having J=0 ground state, possess non-zero magnetic moment. Our studies on EuVO4 reveal three different regions, having different features in magnetic susceptibility. The high temperature susceptibility exhibits linear dependence on temperature which arises due to inter-mixing of ground and excited states, followed by a temperature independent plateau-like region, ascribed to Van Vleck paramagnetism. At low temperatures, Curie-Weiss like behaviour is observed, which arise due to magnetic Eu2+ ions and results in non-zero effective moment. Our analysis reveals that the separation (λ) between the J=0 and 1 states decreases on increasing the external magnetic field which leads to an enhanced effective moment at higher fields.

Erratum: High temperature susceptibility measurements: A potential tool for the identification of oil water transition zone in petroleum reservoirs

An erratum on: Abdulkarim MA, Muxworthy AR and Fraser A (2022) High temperature susceptibility measurements: A potential tool for the identification of oil-water transition zone in petroleum reservoirs. Front. Earth Sci. 10:973385. doi: 10.3389/feart.2022.973385 Due to a production error, an incorrect version of Figure 5 was included in the published article. The correct version of Figure 5 appears below. The publisher apologizes for this mistake. FIGURE 5. Example results from the HT-χ measurements carried out on the Bonneville samples. The magnetic minerology of the ‘main’ oil leg is dominated by siderite. The oil-water region presents a diminished siderite signature and the presence of hexagonal pyrrhotite. Note that the oil-water contact (OWC) marked is as obtained via well logs and pressure analysis. The original version of this article has been updated.

Two new cubic perovskite oxides Ba3CoSb2O9 and Ba2SrCoSb2O9: Syntheses, crystal structures and magnetic properties

Two new cubic perovskite oxides Ba3CoSb2O9 and Ba2SrCoSb2O9 were prepared and characterized. Ba3CoSb2O9 was prepared in polycrystalline form by high-pressure (HP) high-temperature treatment of the hexagonal 6H polytype of Ba3CoSb2O9. Polycrystalline samples of Ba2SrCoSb2O9 were obtained at ambient pressure by a solid-state reaction method. Combined Rietveld refinements of X-ray and neutron diffraction patterns indicated that HP Ba3CoSb2O9 and Ba2SrCoSb2O9 both crystallize in a Fm3¯m cubic double perovskite A2BB’O6 structure with formulae Ba2(Sb0.83Co0.17)(Co0.5Sb0.5)O6 and (Ba1.33Sr0.67)Sb(Co0.7Sb0.3)O6, respectively. Electron diffraction results obtained for Ba2SrCoSb2O9 showed no sign of additional periodicity. Weiss temperatures extracted from high-temperature magnetic susceptibility data were θ ​≈ ​−113 ​K and −118 ​K for HP Ba3CoSb2O9 and Ba2SrCoSb2O9, respectively. HP Ba3CoSb2O9 displays a weak ZFC-FC magnetic irreversibilty below 8 ​K. Ba2SrCoSb2O9 exhibits a spin freezing at Tf ​≈ ​6 ​K, and μSR and 121Sb NMR data revealed a magnetic transition towards a disordered ground state.

Analysis of Rejuvenating Fiber Asphalt Mixtures' Performance and Economic Aspects in High-Temperature Moisture Susceptibility.

Non-renewable resources such as natural stone and asphalt are in short supply. Recycling technology, with its lower cost, has been used as the primary approach to asphalt pavement maintenance engineering. The inclusion of reclaimed asphalt pavement materials in producing new asphalt pavements may increase the risk of cracking. The strength and toughness of the asphalt mixture can be reduced. In this study, Hamburg wheel tracking tests (HWTT) were performed on rejuvenated asphalt mixtures with distinct maintenance processes. Different kinds of fibers have been used as additives to reinforce the rejuvenated asphalt mixtures. The HWTT rutting curve was identified as having three stages, including the post-compaction stage, the creep stage, and the stripping stage. The three-stage rutting curve model was used to determine the intersection point between the creep stage and stripping stage. The other two feature points (i.e., the post-compaction point and the stripping inflection point) were redefined with a new calculation method. Then, the rutting effect and stripping effect were separated with these feature points. The performance and economic benefits of fiber-reinforced rejuvenated asphalt mixtures were investigated through grey correlation analysis under the three maintenance processes. The feature points of the HWTT curve and the cost of the corresponding maintenance process were selected as the impact factors. Finally, the optimal scheme was developed by analyzing the influence of each factor on both performance and economic benefits.

Itinerant antiferromagnetism in Co3S4−δ

We present experimental and theoretical investigations for the cobalt thiospinel ${\mathrm{Co}}_{3}{\mathrm{S}}_{4\ensuremath{-}\ensuremath{\delta}}$. High-quality samples of ${\mathrm{Co}}_{3}{\mathrm{S}}_{4\ensuremath{-}\ensuremath{\delta}}$ $(\ensuremath{\delta}\ensuremath{\sim}0.1)$ were prepared so as to measure their intrinsic properties. The measurements of magnetic susceptibility, specific heat, and electrical transport consistently indicate an antiferromagnetic transition at $\ensuremath{\sim}60$ K, which is attributed to long-range magnetic ordering in the $\mathrm{Co}(A)$ ($A$-site Co ions) diamond sublattice. In addition, there exists a short-range magnetic ordering at around 120 K associated with the magnetic frustrations. The high-temperature magnetic susceptibility obeys Curie-Weiss law, from which a small effective magnetic moment of $1.0\phantom{\rule{0.28em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}$ per formula unit is yielded. The main experimental results can be interpreted by the density-functional-theory calculations with a Hubbard $U$ correction of $\ensuremath{\sim}0.5$ eV. Combining the experimental measurements with the theoretical calculations, we conclude that ${\mathrm{Co}}_{3}{\mathrm{S}}_{4}$ represents a rare example of itinerant-electron diamond-lattice antiferromagnet with moderate electron correlations.

High temperature susceptibility measurements: A potential tool for the identification of oil-water transition zone in petroleum reservoirs

Determining the position and thickness of the oil-water transition zone (OWTZ) in hydrocarbon reservoirs is important to reserve estimation and production planning. This paper describes a magnetic method of identifying this zone. High temperature susceptibility (HT-χ) measurements on core samples from Paleogene reservoirs of the UK Central North Sea revealed distinct signatures around the oil water interface. Rapid increases in susceptibilities at temperatures &amp;lt;250°C were observed for samples around the oil water interface unlike the main oil leg where alteration involving increase in susceptibility occurred at significantly slower rates and higher temperatures. The HT-χ data together with Mössbauer measurements revealed that the variation in alteration characteristics is due to the increasing concentration of hexagonal pyrrhotite and/or lepidocrocite around the oil water interface. Hexagonal pyrrhotite was identified in reservoirs existing at temperatures of &amp;lt;80°C, while lepidocrocite dominated the signature around the contact of deeper reservoirs. These observations suggest that the precipitation of hexagonal pyrrhotite is related to OWTZ centred biogenic activities i.e., biodegradation. The dominance of lepidocrocite in deeper diagenetic settings has been related to hydrolysis of hydrocarbon at the oil water interface, together with cessation of biogenic activities.

High-temperature magnetic susceptibility in metal-electron systems

High-temperature magnetic susceptibility is studied using the Hubbard model. The equation in the high-temperature limit is derived from the Kubo formula as the Curie law of Ns free 1/2-spins, where Ns is the average number of electrons not forming singlets. Exact results for Ns are presented for various cases and are shown to depend only on the total number of electrons Ne and available orbital states, which is the number of lattices L in the single-band case. The condition of kBT≫U, W with the onsite repulsion U and bandwidth W gives Ns=Lp(2−p)/2 with filling p=Ne/L. The numerical calculation for U=0 shows that the universal Curie law holds at temperatures above the threshold temperature T0, compatible with the Fermi temperature. The threshold temperature for U>0 is found to be lower than T0. The application of the present results to a heavy-fermion system near the Mott transition is proposed.

Differential Thermal Analysis Using High Temperature Susceptibility Instruments

AbstractMeasurements of susceptibility as a function of temperature are an important, standard method of quantifying a sample's magnetic mineralogy. These measurements are used to identify the Curie/Néel temperatures of constituent minerals and show evidence of thermally induced oxidation and formation of magnetic minerals. For these reasons, the High Temperature Susceptibility Bridge (HTSB) is a common instrument in paleomagnetism laboratories around the world. Here, we argue that HTSBs can be used to perform simple differential thermal analysis, a technique used to identify phase transitions and exo‐/endothermic reactions by measuring deviations in temperature from a steady heating rate. Because HTSBs are designed to heat samples at a relatively constant rate, the standard susceptibility measurement can be used to obtain similar information, albeit crude, about the phase transitions taking place. For standard samples of vivianite, goethite, and maghemite, we compare the heating curves of the sample and a blank run, to identify DTA‐analogous information. In the case of goethite and vivianite, the reactions identified do not have a corresponding expression in susceptibility, demonstrating that this approach expands the utility of this common piece of equipment. We estimate the minimum enthalpy of reactions detectable and their mass dependence. Additionally, we show that this approach is successful in detecting the dehydration of vivianite in a mixed mineralogy natural sample.

Rock magnetic fingerprint of Mt Etna volcanic ash

SUMMARYA detailed rock magnetic study was conducted on ash samples collected from different products erupted during explosive activity of Mount Etna, Italy, in order to test the use of magnetic properties as discriminating factors among them, and their explosive character in particular. Samples include tephra emplaced during the last 18 ka: the benmoreitic Plinian eruptions of the Pleistocene Ellittico activity from marine core ET97-70 (Ionian Sea) and the basaltic Holocene FG eruption (122 BC), the Strombolian/Phreatomagmatic/sub-Plinian eruptions (namely, the Holocene TV, FS, FL, ETP products and the 1990, 1998 eruptions) collected from the slope of the volcano, and the Recent explosive activity (lava fountains referred to as ‘Ash Rich Jets and Plumes’, or ARJP) that occurred in the 2001–2002 period, related to flank eruptions. Mössbauer spectrometry informs that a single magnetic mineral dominates the three groups, which are characterized by variable magnetic grain sizes and composition. Detailed rock-magnetic investigations, ranging from low temperature to high temperature remanence and susceptibility experiments, indicate that the more explosive products of the Plinian eruptions and ARJP activity tephra, are characterized by oxidized Ti-rich titanomagnetites, with dominant Curie Temperatures between 230 and 330 °C. The FG and ARJP tephra are also characterized by contrasting, yet overall higher, coercivity distributions and higher magnetizations and susceptibilities, including below room temperature. In contrast, most of the Strombolian/sub-Plinian eruptions have a magnetic signature dominated by less coercive magnetite and/or Ti-poor titanomagnetite. Magnetic differences observed between the Late Pleistocene and Holocene FG Plinian eruptions can be attributed to the different composition of the former eruptions, which were fed by more evolved magmas, whereas geochemical variations characterizing the products erupted in the last few decades can be responsible for the differences between the Holocene and recent Strombolian/sub-Plinian products. Importantly, detailed magnetic investigation of sideromelane and tachylite clasts, the two end members of the juvenile fraction extracted from the ash of the most explosive products, determines that the tachylite fraction is responsible for the magnetic signature of the Plinian FG and ARJP tephra, and is attributed to the intense fragmentation that characterizes these activities, likely resulting from undercooling processes. Moreover, the abundant superparamagnetic grains associated with these eruptive styles are believed to represent the nanolite fraction responsible for the increasing viscosity of these magmas, and to be responsible for their explosive character. The distinctive magnetic properties that characterize the tachylite-bearing tephra, representative of the fragmentation process that distinguishes the most explosive activities, provides a useful magnetic tool that can complement traditional volcanological investigations.

DNA Methylation Alterations and Their Association with High Temperature Tolerance in Rice Anthesis

DNA methylation is an important epigenetic mechanism involved in gene regulation under environmental stresses in plants. However, little information is available regarding its responses to high temperature (HT) and association with HT tolerance in rice. In this study, fourteen rice genotypes were classified into the susceptible, moderate, and tolerant groups by the high temperature susceptibility index (HTSI) after HT treatment. The changes of DNA methylation in rice anthesis under normal and HT30 conditions were investigated using methylation-sensitive amplified polymorphism31 (MSAP). The MSAP results showed that the DNA methylation level significantly increased in the susceptible rice group and decreased in the tolerant rice group under HT treatment, while no significant difference was observed in the moderate rice group. More hypomethylation events were detected in the tolerant rice group, while more hypermethylation was detected in the susceptible rice group. Forty-four differentially methylated epiloci (DME) were generated under both control and HT conditions, which can clearly distinguish the susceptible, moderate, and tolerant genotypes via PCoA analysis. Approximately 43.18% of DMEs were determined to be tolerance-associated epiloci (TAEs). 63.15% TAEs were sequenced and annotated into 12 genes. Quantitative RT-PCR analysis showed that 12 TAE genes were mainly upregulated in 14 rice genotypes, and their expression levels were related to the HT tolerance of rice. Here, DEGs, generated from a number of genotypes, indicate higher probabilities for association with stress tolerance. Overall, these results suggest that DNA methylation regulation might play a key role in adaptation to HT stress in rice.

Frustrated magnetism of the triangular-lattice antiferromagnets α-CrOOH and α-CrOOD

We report a comprehensive investigation of the frustrated magnetism on the delafossite oxides, α-CrOOH and α-CrOOD, which experimentally realize the S = 3/2 nearly-Heisenberg antiferromagnetic (J 1 > 0) model on a triangular lattice with weak single-ion anisotropy (D). The electron spin resonance (ESR), neutron scattering, and specific heat (C m) measurements on both α-CrOOH and α-CrOOD consistently indicate that the long-range 120° Néel order is significantly suppressed and both systems are in the vicinity of a spin-liquid phase with C m ∼ T 2 at low temperatures. The strength of D is quantitatively determined from fitting the high-temperature ESR linewidth and magnetic susceptibility, and its minus sign (D < 0, easy-axis type) is suggested by the low-energy (E ⩽ 2 meV) spin excitations. This easy-axis anisotropy (D/J 1 ∼ −5%) competes with the 120° Néel order and thus enhances the quantum spin fluctuations at low temperatures.

Gapless Quantum Spin Liquid in the Triangular System Sr_{3}CuSb_{2}O_{9}.

We report gapless quantum spin liquid behavior in the layered triangular Sr_{3}CuSb_{2}O_{9} system. X-ray diffraction shows superlattice reflections associated with atomic site ordering into triangular Cu planes well separated by Sb planes. Muon spin relaxation measurements show that the S=1/2 moments at the magnetically active Cu sites remain dynamic down to 65mK in spite of a large antiferromagnetic exchange scale evidenced by a large Curie-Weiss temperature θ_{CW}≃-143 K as extracted from the bulk susceptibility. Specific heat measurements also show no sign of long-range order down to 0.35K. The magnetic specific heat (C_{m}) below 5K reveals a C_{m}=γT+αT^{2} behavior. The significant T^{2} contribution to the magnetic specific heat invites a phenomenology in terms of the so-called Dirac spinon excitations with a linear dispersion. From the low-T specific heat data, we estimate the dominant exchange scale to be ∼36 K using a Dirac spin liquid ansatz which is not far from the values inferred from microscopic density functional theory calculations (∼45 K) as well as high-temperature susceptibility analysis (∼70 K). The linear specific heat coefficient is about 18 mJ/mol K^{2} which is somewhat larger than for typical Fermi liquids.

Effect of Thermochromic Materials on the Properties of SBS-Modified Asphalt Mixture

Styrene-butadiene-styrene copolymers (SBS)–modified asphalt mixture is widely used in high grade roads because of its excellent comprehensive performance. However, the black characteristics and high temperature susceptibility of asphalt binder have a great impact on the performance of asphalt mixture. This paper mainly investigates the influence of different types of thermochromic materials on the properties of SBS-modified asphalt mixture, including high- and low-temperature performance, water stability, and the aging effect of the natural environment on asphalt mixture (natural aging). According to test results, thermochromic materials slightly reduce the high-temperature performance of SBS-modified asphalt mixture. All three kinds of thermochromic materials can improve the low-temperature crack resistance of SBS-modified asphalt mixture, among which red thermochromic material with 2% content (named as 2%RTP) is the best. In addition, thermochromic materials of different colors can improve the water stability of SBS-modified asphalt mixture, and black thermochromic material with 2% content (named as 2%BTP) exhibits the best effect on improving the water stability. All three thermochromic materials can improve the antinatural aging property of SBS-modified asphalt mixture.