Total Magnetic Susceptibility Research Articles

Magnetic properties and compensation temperatures of a graphene bilayer by Monte Carlo simulation

We used Monte Carlo simulation to study the magnetic properties and compensation behavior of a ferrimagnetic mixed-spin (3/2; 1/2) Ising system in a graphene bilayer. The effects of exchange interactions, crystal field, external magnetic field and temperature on the total magnetization, partial magnetizations, magnetic susceptibility, phase diagram and hysteresis behavior of the system were examined. Interesting results were obtained in this work, such as the compensation behavior and the multi-loop hysteresis phenomenon for specific values of the system’s physical parameters. Our results conform to those of other theoretical studies.

Mean-field study of magnetic properties and hysteresis behavior in a bilayer graphene Ising system

Using the mean-field approximation based on the Gibbs-Bogoliubov inequality for the free energy, we conducted an investigation into the magnetic properties and hysteresis behavior of a graphene Ising bilayer, where the top and bottom layers are occupied by spins σ = 3/2 and S = 5/2, respectively. The effects of exchange interactions, crystal fields, external magnetic field and temperature on the total magnetization, partial magnetizations of each layer, total magnetic susceptibility, blocking temperature and hysteresis loops of the system were thoroughly analyzed. The variations of the blocking temperature as a function of various parameters in the system’s Hamiltonian were presented. Furthermore, we demonstrated the existence of multiple hysteresis loop behaviors under specific physical conditions.

Detection of brown adipose tissue in rats with acute cold stimulation using quantitative susceptibility mapping.

Detection of brown adipose tissue in rats with acute cold stimulation using quantitative susceptibility mapping.

Modern conditions and recent environmental evolution of the industrialized inner Ría of Ferrol (Galicia, NW Spain)

Galician rías provide several ecosystem services of great ecological and economic significance in the northwestern Iberian margin, requiring a good environmental quality for sustainable harnessing. More paleoenvironmental reconstructions extending to their preindustrial state are needed to predict their evolution under natural and human-induced perturbations, such as ongoing anthropogenic global warming. This study's aim is twofold: first, characterize the current environmental conditions governing the inner Ría of Ferrol (Galicia, NW Spain) and address its recent natural and anthropogenic evolution. Therefore, a multiproxy approach (benthic foraminifera, grain size, pollen content, trace metals, Al, total organic and inorganic carbon contents, total nitrogen content, δ13C, magnetic susceptibility, 210Pb and 137Cs radiotracers, and microplastics) has been applied to intertidal surface and sediment core samples. The benthic foraminiferal results exhibit typical inner ría assemblages, primarily driven by natural ría-estuarine dynamics, with a higher dominance of brackish species (H. germanica, A. morphogroup tepida), fewer living individuals and marine allochthonous taxa toward the continental end-member. The foraminiferal standing crops and surface trace metal concentrations do not reflect strong anthropogenic impacts, although areas with elevated magnetic susceptibility have been detected, probably associated with nearby industrial activities. The recent sedimentary deposits reveal anthropogenic impacts at local and regional scales, with different environmental shifts. Local impacts were triggered by physical interventions in the inner ría, with the construction of the As Pías Bridge in 1968 and the great urban-industrial development of Ferrol city and surrounding localities experienced since the late 19th century. Land-use changes have driven regional scale changes, corresponding to reforestation plans with the introduction of anthropogenic plant species for industrial purposes initiated in the 1940s. The stratigraphic analysis of sediment cores has unveiled high levels of contaminants (Zn and microplastics) in the innermost sector as the primary environmental concerns. In this sediment-infilling and restricted area, potential dredging activities could release them leading to their possible bioavailability. Although past adverse environmental conditions cannot be discarded, sedimentary intervals with negligible presence of microfauna in the innermost area have mostly been attributed to taphonomic processes involving calcareous dissolution and disaggregation of agglutinated tests, likely caused by carbonate-undersaturated conditions and organic matter metabolization by microbial activity respectively.

Magnetic Properties of CuCr1−xLaxS2 Thermoelectric Materials

The magnetic properties (magnetic susceptibility, magnetic moment) and Weiss constant for lanthanum-doped CuCr1−xLaxS2 (x = 0; 0.005; 0.01; 0.015; 0.03) solid solutions were studied using static magnetochemistry at 80–750 K. The samples were characterized by both powder X-ray diffraction and energy-dispersive X-ray spectroscopy. It was shown that synthesized samples are single-phased up to x ≤ 0.01. The presence of the additional phase in the solid solutions with x > 0.015 caused deviation from the simple isovalent Cr3+→Ln3+ cationic substitution principle. It was found that magnetic susceptibility and the Weiss constant are significantly affected by both magnetic properties and lanthanum concentration for the solid solutions doped up to x = 0.01. The largest magnetic moment value of 3.88 µB was measured for the initial CuCrS2-matrix. The lowest value of 3.77 µB was measured for the CuCr0.99La0.01S2 solid solution. The lowest Weiss constant value of −147 K was observed for the initial matrix; the highest one was observed for CuCr0.99La0.01S2 (−139 K). The largest Seebeck coefficient value of 373 µV/K was measured for CuCr0.985La0.015S2 at 500 K; the obtained value was 3.3 times greater compared to the initial CuCrS2-matrix. The field dependence of the magnetic susceptibility allowed one to conclude the absence of ferromagnetic contributions in the total magnetic susceptibility of CuCr1−xLaxS2. The data on magnetic properties can be successfully utilized to investigate the limits of doping atom suitability and order–disorder phase transition temperature in CuCrS2-based solid solutions.

The effect of an external magnetic field, doping, and bias voltage on the thermoelectric and thermodynamic of S-graphene monolayer

In the present report, we studied the thermoelectric and thermodynamic properties of the S-graphene (SG) monolayer under the effect of the external magnetic field, electron/hole doping, and bias voltage by the tight-binding (TB) model. The Green function method has been applied for calculating the electronic heat capacity, Pauli magnetic susceptibility, electronic thermal conductivity, Seebeck coefficient, and electrical conductivity of the SG monolayer. The results show that the electronic heat capacity increases by the magnetic field, which is in agreement with Einstein's Debye relation. It has been observed that the SG monolayer can act as a p-type or n-type semiconductor by applying the studied parameters (doping, external magnetic field, and bias voltage), which means the semiconductor type of SG is controlled by electron/hole doping and applying magnetic field, and bias voltage. Our results show that the SG monolayer is a paramagnetic material, but it depends on bias voltage and external magnetic field. Also, the total Pauli magnetic susceptibility is enhanced in the presence of an external magnetic field.

Effect of vacancy defects on geometrically frustrated magnets

Quenched disorder may prevent the formation of the widely sought quantum-spin-liquid states (QSLs) or mask their signatures by inducing a spin-glass state, which is why considerable experimental efforts are directed at purifying materials that may host QSLs. However, in geometrically frustrated (GF) magnets, the largest class of materials in which QSLs are sought, the glass-transition temperature $T_g$ grows with decreasing the density of vacancy defects, accompanied by a simultaneous growth of the magnetic susceptibility. In this paper, we develop a phenomenological theory of glass transitions and magnetic susceptibility in 3D geometrically frustrated (GF) magnetic materials. We consider a model of a GF magnet in which the glass transition occurs in the absence of vacancies, e.g., due to other types of quenched disorder. We show that disorder that creates weak local perturbations, e.g. weak random strain, leads to the growth of the transition temperature $T_g$. By contrast, vacancies reduce $T_g$ for small vacancy concentrations. Another consequence of the presence of vacancies is the creation of quasispins, effective magnetic moments localised near the vacancies, that contribute to the magnetic susceptibility of the system together with the bulk spins. We show that increasing the vacancy density leads to an increase of the total magnetic susceptibility.

Geochemistry signatures of mercury in soils of the Amazon rainforest biome

Mercury (Hg) toxicity in soils depends on Hg species and other physical and chemical attributes, as selenium (Se) hotspots in soils, particularly relevant in Amazonian soils. The study of Hg species and their relations in representative locations of the Amazon rainforest biome is critical for assessing the potential risks of Hg in this environment. This work aimed to determine the concentration of total Hg and its species (Hg0, Hg22+ and Hg2+), and to correlate Hgtotal concentration with total elemental composition, magnetic susceptibility, and physicochemical attributes of Amazon soils. Nine sites in the Amazon rainforest biome, Brazil, were selected and analyzed for their chemical, physical, and mineralogical attributes. The clay fraction of the studied Amazon soils is dominated by kaolinite, goethite, hematite, gibbsite, and quartz. Mica was also found in soils from the States of Acre and Amazonas. Hgtotal ranged from 21.5 to 208 μg kg−1 (median = 104 μg kg−1), and the concentrations did not exceed the threshold value established for Brazilian soils (500 μg kg−1). The Hg2+ was notably the predominant species. Its occurrence and concentration were correlated with the landscape position and soil attributes. Hgtotal was moderately and positively correlated with TiO2, clay, and Se. The findings showed that geographic location, geological formation, and pedological differences influence the heterogeneity and distribution of Hgtotal in the studied soil classes. Thus, a detailed characterization and knowledgment of the soil classes is very important to clarify the complex behavior of this metal in the Amazon rainforest biome.

Evaluating the properties of the intermetallic compound HoN for magnetic refrigerator application: Combined DFT and Monte Carlo simulation

Evaluating the properties of the magnetocaloric material regenerators is a crucial step in order to exploit them subsequently as the working substances in magnetic cooling devices. So, the main objective of this latter is to evaluate the electronic, magnetic properties as well as the magnetocaloric effect of HoN compound. To do so, a combination of DFT study and Monte Carlo simulations has been performed on HoN compound which undergoes a second-order ferromagnetic-paramagnetic phase transition. For this material, the temperature-dependent total magnetization, heat capacity and magnetic susceptibility have been calculated and are revealed that the curie temperature is acceptable concurrence with the experimental value. Furthermore, it was showed that under an applied magnetic field of 5T, the magnetocaloric effect (MCE) in regard to the maximum value of magnetic entropy change ΔSmagmax around its Curie temperature, agree well with the experimental one. Besides, the relative cooling power (RCP) values are found to be 28.5, 162.2 and 227 J. Kg−1 under different magnetic fields of 1,3 and 5T. All findings which are presented in the present work indicate that the large values of RCP and ΔSmagmax found in HoN are interesting for low-temperature magnetic refrigeration with excellent performance.

Environmental Fate of Trace Elements in Depositional Sediments after Flashflood Events: The Case of Mandra Town in Greece

Flash floods are one of the harshest natural hazards, having a wide range of substantial impacts for human and environmental health in the short-term and long-term. On 15 November 2017, a high-intensity storm caused a catastrophic flash flood event in the town of Mandra, a western, outer suburb of the Athens Metropolitan Area in Greece. In this study, we determine the aqua regia extractable concentrations of trace elements in residual sediments and associated soils after the flash flood and evaluate the fractionation of contaminants in geochemical compartments. Geochemical data are coupled with physicochemical parameter measurements and mineralogy to identify possible factors explaining the variability of trace element concentrations, while a dilute acid extraction is used to monitor changes of the reactive fraction of the trace elements over the term of 1 year following the flood event. Aqua regia concentrations in flood-deposited sediments reached values of 1 mg/kg (Cd), 24 mg/kg (Co), 183 mg/kg (Cr), 599mg/kg (Cu), 1080 mg/kg (Mn), 195 mg/kg (Ni), 122 mg/kg (Pb) and 945 mg/kg (Zn). Multivariate statistical techniques classified the elements according to their natural or anthropogenic origin. Trace elements of geogenic origin (As, Co, Cr, Mn, Ni) dominate in flood deposited material. The cluster of anthropogenic elements (Cd, Cu, Pb, Zn,) shows significant correlation with total organic carbon and magnetic susceptibility, while a significant seasonal variation has been observed for total organic carbon, Cd and Mn contents in the deposited sediments. Results allow a better understanding of the distribution of elements in the surface cover during and after catastrophic events in urban areas and provide useful information on the long-term exposure of the residents.

Spin compensation, critical and discontinuous transitions behaviors in a ferrimagnet of spins 5/2 and 7/2

We apply Monte Carlo simulation techniques to study the magnetic behavior of a mixed ferrimagnetic Ising model on sites of a square lattice of LxL size, with L = 120, where 5/2 spins are alternated with 7/2 spins. We consider an antiferromagnetic interaction next-neighbor, ferromagnetic interactions next-nearest-neighbor, and an external magnetic field in the Hamiltonian that defines the model. We characterize the effects of an external magnetic field on the behavior of the system through the analysis of spin compensation points, discontinuous transitions, and hysteresis loops at various temperatures in the total magnetization and magnetic susceptibility. At the end, we study the phase diagrams of the critical, compensation and discontinuous transition temperatures. The physical phenomena experienced by the system under study are relevant to the application in magneto-optical recordings, in the synthesis and construction of molecular-based magnets and have technological applications in the manipulation and storage of magnetic information. We found some phenomena not reported in previous works on the same system.

Magnetic properties and phase diagrams of the mixed spin-(1 2, 3 2) Ising–Heisenberg model in the mean field approximation

In this paper, the effects of the longitudinal [Formula: see text] and the transverse [Formula: see text] crystal fields on the mixed spin-[Formula: see text] Ising–Heisenberg model have been studied. The thermodynamic properties of the model are obtained by using a new approach of the mean field approximation (MFA). The thermal variations of the order-parameters and the total magnetic susceptibility of the model are carefully investigated to obtain the phase diagrams on the [Formula: see text] planes for [Formula: see text] and on the [Formula: see text] planes for [Formula: see text] and 6. The existence of compensation temperatures between the sublattice magnetizations, [Formula: see text], and the two components of the quadrupole moments, [Formula: see text], are observed. Our results are compared with other existing works in the literature and reliable agreements are found.

Revisiting the magnetic and magnetocaloric properties of bulk gadolinium: A combined DFT and Monte Carlo simulations

In this paper, a combination of DFT study and Monte Carlo (MC) simulations has been performed on Gd compound which undergoes a second–order phase transition from ferromagnetic state to paramagnetic one. For this single material, the temperature-dependent total magnetization and magnetic susceptibility have been calculated and are revealed that the Curie temperature is acceptable concurrence with the experimental value. Furthermore, it was showed that under an external magnetic field of 2 Tesla (T), MCE of Gd compound around its Curie point in regard to the maximum value of magnetic entropy change (), agrees well with the experimental one. Besides, the Relative Cooling Power (RCP) values are found to be 34.37, 69.18, 90.74 and 128 J.kg−1 under different magnetic fields of 0.5, 1.0, 1.5 and 2T, respectively. All findings which are presented here indicate that DFT calculations and Monte Carlo simulations can be efficiently used to predict the magnetic and magnetocaloric features of Gd and related alloys.

Zones of inelastic deformation around surface ruptures detected by magnetic fabrics

Characterizing the inelastic strain field around co-seismic faults is a key to understanding earthquake rupture processes. We aim to detect zones of inelastic deformation around surface ruptures, using Anisotropy of Magnetic Susceptibility (AMS) analyses. To characterize the paleo-seismic setting we measured 29 normal faults, which cut the late Pleistocene lacustrine Lisan Formation and were associated with shallow (<~12 km) earthquakes at the margins of the Dead Sea Basin. In order to define the geometry of those zones around a representative fault, 220 specimens were sampled in a 2D grid and analyzed by studying the room temperature AMS axes and parameters using spatial IDW (inverse distance weighting) interpolation on a cross section around the fault plane. To separate the total magnetic susceptibility of the Lisan sediments into diamagnetic, paramagnetic and ferromagnetic susceptibilities, we applied the low temperature AMS (LT-AMS) and Anhysteretic Remanent Magnetization (AARM) methods. The structural measurements demonstrate that the co-seismic faulting in the Dead Sea Basin, triggered mainly by E-W extension. The results show that the paramagnetic phase is dominant in both the aragonite-rich and the detritus-rich layers. The zones of inelastic deformation are distributed asymmetrically about the fault plane, with affinity to the observed displacement profile and in agreement with dynamic propagation models that suggest that the rupture propagated towards the surface. The discontinuous distribution of deformation around the fault plane is the result of both the faults single event propagation style and fault plane asperities. These results demonstrate a novel application of AMS analysis for defining the geometry of the inelastic strain field surrounding co-seismic faults, and improving fault propagation models dealing with the inelastic off-fault response.

High-resolution records of Oceanic Anoxic Event 2: Insights into the timing, duration and extent of environmental perturbations from the palaeo-South Pacific Ocean

Oceanic Anoxic Event 2 (OAE 2), which took place around the Cenomanian–Turonian boundary (∼94 Ma), is associated with extreme perturbations to the global carbon cycle, affected ocean basins worldwide and was associated with significant biological turnover. Although this event has been well studied in the northern hemisphere, the evolution and character of OAE 2, particularly in terms of the vertical and lateral extent of anoxia, is poorly constrained in the palaeo-Pacific Ocean. Furthermore, the precise timing, duration and character of this event, and the exact mechanisms driving OAE 2 environmental changes, are still being debated. Here, we present the first high-resolution records of carbon isotopes, total organic carbon and magnetic susceptibility from the southern palaeo-Pacific Ocean during OAE 2, sampled at two sections in New Zealand. The carbon isotope records from both localities reveal a ∼2‰ positive excursion that represents the global change in the carbon cycle associated with OAE 2. When combined with a cyclostratigraphic age model, these new records constrain the duration of the OAE 2 carbon isotope excursion to at least 930 ± 25 ky and indicate a minimum duration of 200 ± 25 ky for the ‘Plenus Cold Event’ that took place during OAE 2. The lithologies and low organic-carbon contents of the New Zealand sections imply that oxic conditions prevailed along, at least parts of, the margins of the palaeo-Pacific Ocean at mid- to high southern latitudes during OAE 2 while, contemporaneously, conditions were locally anoxic in the mid-water column of the equatorial Pacific Ocean. Despite these apparently oxic conditions in the New Zealand region, there was a partial collapse of benthic ecosystems leading up to, and during, OAE 2, suggesting environmental deterioration caused by intermittent oxygen deprivation, or other chemical or biological disturbances in the South Pacific region that remain to be elucidated.

Iron speciation in sediment cores near the Jiulong Methane Reef and its implication

Variability in iron species in marine deposits are excellent geochemical archives for exploring variations in redox conditions during early diagenesis and seepage dynamics over time. Two sediment cores (DS07 and DS08) were collected in the Jiulong Methane Reef, a typical cold seep site that is located in the South China Sea (SCS), and analyzed for iron species using Mössbauer spectrometry and magnetic procedures. Excluding the surface layer (0-10 cm) in DS07, Fe2+/Fe3+ ratios indicated that core sediments were under anoxic conditions. The Fe2+/Fe3+ and frequency-dependent susceptibility (χfd) at this site were higher while the total organic matter content (TOC) and magnetic susceptibility (χ) were significantly lower at approximately 170 cm depth. Combined with chromium reducible sulfur (CRS), Fe/Al and sulfur to organic content (S/C) ratios suggested that there was a sulfate-methane transition zone (SMTZ) at approximately 170 cm. Moreover, thermomagnetic analyses indicated that magnetite was the dominant ferrimagnetic mineral at 21–23 cm, 165–185 cm, 213–233 cm and 285–295 cm depths, however, magnetite content was relatively lower between the 165 and 185 cm depth, which suggested that magnetite had been largely transformed to paramagnetic iron minerals during the anaerobic oxidation of methane (AOM) process. The DS08 sediment core was also mostly anoxic , however, no obvious methane seepage activity was observed because the maximum values of Fe2+/Fe3+, Fe/Al, CRS, S/C and the minimum values of TOC and χ did not simultaneously occur at the same depth. The study revealed that the speciation of Fe in sediment cores varied under different redox conditions which was of interest when utilizing iron speciation and magnetic minerals as indicators of historical environmental conditions and seepage activities.

Phytolith-inferred transfer function for paleohydrological reconstruction of Dajiuhu peatland, central China

Depth to water table (DWT, the depth from the water surface to the top of the peat surface) is one of the most important environmental variables related to the habitat types and distribution of vegetation within a subalpine peatland. The distribution of phytolith assemblages and basic environmental data from 43 surface soil samples with significant ecological and hydrological gradients were investigated to generate transfer functions for quantitative reconstruction of paleoenvironmental changes in Dajiuhu peatland, central China. Detrended correspondence analysis (DCA) and redundancy analysis (RDA) were employed to explore the relationship between main environmental variables and phytolith morphotypes and distributions. Our results indicate that the spatial distribution of phytoliths was significantly correlated with the DWT (25% variance), total organic carbon (TOC, 10% variance) and magnetic susceptibility (χ, 7% variance). We established the transfer functions for the significant variables based on modern analogue technique (MAT), weighted averaging techniques (WA) and weighted averaging partial least squares (WA-PLS), and model performance was assessed using bootstrap cross-validation. The high correspondence of the predicted DWT results based on phytolith-environment calibration data with observed data reflects that the phytolith-based WA-PLS is a reliable effective calibration method for the quantitative DWT reconstruction of ombrotrophic (rain-fed) subalpine peatland.

Quantum Monte Carlo study of dynamic magnetic properties of nano-graphene

Using the Quantum Monte Carlo simulation (QMCS), the dynamic blocking temperature of a nano-graphene bilayer has been investigated within the framework of the Transverse Ising Model (TIM) with mixed spins, under the existence of the time-dependent oscillating longitudinal magnetic field (h(t)=hb+h0cos(ωt)) and the transverse field (Ω). The influence of the time-dependent oscillating longitudinal magnetic field, the period of magnetic field (τ) and the transverse field (Ω) on the thermal behavior of the total longitudinal and transverse dynamic order parameters, the total dynamic magnetic susceptibility and the dynamic hysteresis of the nano-graphene bilayer are also studied. As results, we remark the appearance of multiple hysteresis loops and the system exhibits the superparamagnetic behavior at the dynamic blocking temperature.

Quantitative susceptibility mapping (QSM) as a means to monitor cerebral hematoma treatment.

Quantitative susceptibility mapping (QSM) offers a consistent hemorrhage volume measurement independent of imaging parameters. To investigate the magnetic susceptibility of intracerebral hemorrhage (ICH) as a quantitative measurement for monitoring treatment in hematoma patients. Prospective. Twenty-six patients with acute ICH were recruited and enrolled in treatment including surgery or medication (mannitol) for 1 week. A 3D gradient echo sequence at 3.0T. The hematoma volumes on computed tomography (CT) and QSM were calculated and used for correlation analysis. Magnetic susceptibility changes from pre- to posttreatment were calculated and compared to the National Institutes of Health stroke scale (NIHSS) measure of neurological deficit for each patient. Mean susceptibility values were calculated over each region of interest (ROI). A one-sample t-test was used to assess the changes of total volumes and mean magnetic susceptibility of ICH identified between pre- and posttreatment images (P < 0.05 was considered significant) and the Bland-Altman analysis with 95% limits of agreement (average difference, ±1.96 SD of the difference). Regression of volume measurements on QSM vs. CT and fitted linear regression of mean susceptibility vs. CT signal intensity for hematoma regions were conducted in all patients. Good correlation was found between hemorrhage volumes calculated from CT and QSM (CT volume = 0.94*QSM volume, r = 0.98). Comparison of QSM pre- and posttreatment showed that the mean ICH volume was reduced by a statistically insignificant amount from 5.74 cm3 to 5.45 cm3 (P = 0.21), while mean magnetic susceptibility was reduced significantly from 0.48 ppm to 0.38 ppm (P = 0.004). A significant positive association was found between changes in magnetic susceptibility values and NIHSS following hematoma treatment (P < 0.01). QSM in hematoma assessment, as compared with CT, offers a comparably accurate volume measurement; however, susceptibility measurements may enable improved monitoring of ICH treatment compared to volume measurements alone. 2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018;48:907-915.

Investigation by Monte Carlo simulation of substitution doping in the Double Perovskite Sr2CrRe1−xWxO6

Re-substitution doping by W has been investigated in the Double Perovskite (DP) Sr2CrRe1−xWxO6 for x ranging from 10 to 90% by using a Monte Carlo Simulation (MCS) in the framework of Ising model. Exchange couplings used in the simulation have been approximated in previous work for experimental Curie temperatures (TC). Doping effect on: partial and total magnetization, magnetic susceptibility, internal energy, specific heat, and Curie temperature has been studied. A sharp drop of partial magnetizations at 40% of W-concentration has been noticed at the magnetic transition. Apparition of a non-monotonic behavior of the total magnetization at 20% of W-concentration. Effect of doping on the stability of the compound has been emphasized. A quasilinear decrease of TC has been observed by increasing the concentration percentage of substitution doping by W.