جستجوی مقالات مرتبط با کلیدواژه "پذیرفتاری مغناطیسی" در نشریات گروه "علوم پایه"

In this study, we investigate the trajectory of magnetic nanoparticle flowing through a microvessel in the presence of cylindrical magnet. By using the equation of motion of particle in the presence of magnetic and fluidic forces, the motion trajectory of magnetic particle in the microvessel is calculated. Our numerical results show that the probability of trapping magnetic particles in the straight microvessel is a function of the intensity of the magnetic field, particle radius, particle magnetization, and diameter of vessel. In this study, we investigate the effect of particle radius, magnet magnetization, particle saturation magnetization and vessel radius on the trajectory of magnetic nanoparticle flowing through the straight vessel. The results show that with increasing particle radius, magnet magnetization, particle saturation magnetization and also with decreasing vessel radius, the probability of trapping a floating particle in the channel increases

In this study, the density of states, heat capacity, and magnetic susceptibility of carbon nanodiscs and nanowires with different diameters are calculated via the tight-binding approximation and the Green’s function approach. The results indicate that by increasing the diameter, the nanodiscs move from a semi-conductive and tend toward a semi-metal which is in agreement with other theoretical works. Also, increasing the diameter of the nanowires causes them to exhibit a metallic behavior. It is observed that increasing the diameter of these nanostructures increases the number of the Van Hove singularities in the density of states diagrams. A Schottky anomaly peak is seen in the heat capacity curves of these two nanostructures, which for the nanodisc/nanowire with the largest diameter, has a lower height. Due to the presence of the Van Hove singularities in the density of states diagram, a crossover is seen in the magnetic susceptibility curves, which splits these diagrams into two high temperature and low temperature regions. It is also concluded that at low temperatures, increase in the diameter of the nanodiscs and nanowires increases the magnetic susceptibility. These maximum values are also observed in the heat capacity and magnetic susceptibility curves of other graphene and graphene-like nanostructures.

In this paper, temperature dependence of the magnetic susceptibility of the Mn12 magnetic molecular cluster is investigated in different fields. Until now, only dipole excitations were considered in calculations to calculate magnetic susceptibility, but due to the spin number of this molecular cluster and in order to obtain higher computational accuracy, more multipolar excitations should be included in the calculations. For this purpose, in this paper, in the calculations related to the magnetic susceptibility of the molecule, in addition to dipolar excitations, quadrupole excitations are also considered, and the relevant diagrams are drawn. Calculations show that the results obtained in a situation where quadrupole excitations are considered, are more consistent with the experimental results.

Monitoring the magnetic properties of suspended particles in the air deposited on the leaves of trees provides useful information on the spatial distribution of the suspended particles in urban and industrial areas. This study was carried out to extend and develop the application of peripheral magnometry method to investigate environmental pollution and metal contaminants resulted from vehicle traffic in some areas of Tehran with heavy traffic. The leaves of Platanus Orientalis in the inland areas of Chitgar Park as a clean area and Azadi Square and Geisha Bridge as crowded areas were collected. Magnetic components such as natural magnetic residual, mass magnetic susceptibility, isothermal magnetic residual and saturated induction magnetic residual were measured in the samples. The concentration of copper, iron, lead and cadmium was measured by mass spectrometry and the relationship between magnetic components and metals was investigated. The results showed that the highest value of susceptibility and magnetic residual of leaf saturation was associated with heavier traffic of vehicles in Azadi and Geisha. The study of the composition of particles in the Chitgar showed a combination of hard ferromagnetic minerals such as hematite with high concentration and soft ferromagnetic minerals with low concentration, which are the result of the activities of the peripheral industries and traffic in Tehran-Karaj highway. The presence of soft magnetic minerals in both Azadi and Geisha regions was higher than Chitgar. In Azadi, the size of particles was larger and the mineral behavior indicated a combination of the presence of soft and hard minerals, while the size of particle was smaller in Geisha.

 One of the processes of the Quaternary era is the glacial and interglacial periods. In the glacial period, loesses deposited and in the interglacial period, Paleosoils were formed. The northern part of Iran is geographically the same as countries such as China, a large part of which has been covered with loess sediments during the Pleistocene glacial period. Loess sediments in northern Iran reflect several cycles of climate changes and the evolution of the earthchr('39')s appearance for the middle to late Quaternary period. In this region, the Loes-Paleosoil sequences are one of the most important terrestrial archives of climate change and provide a bridge between Southeast European and Central Asian loess sediments. To reconstruct paleoclimate changes, magnetic susceptibility is used as a climate proxy. The high magnitude of the magnetic susceptibility indicates the large volume of magnetic minerals. Chemical weathering causes the formation of magnetic minerals such as magnetite and maghemitite. These minerals are abundant in Paleosoils and can be determined by analyzing the magnetic susceptibility of Loess and Paleosoils. The magnetic properties of the Loess-Paleosoil sequence are considered to be evidence of paleo precipitation and weathering.Study area Geographical location of Saadabad sedimentary section in the northern region is 36° 49chr('39') N and 54° 22chr('39') E, at an altitude of 140 m a.s.l. Saadabad sedimentary section is located in the construction zone of Alborz and in terms of the main sedimentary-structural zones of Iran is part of the southern Caspian coast. This zone includes areas, which are located in the north of Alborz fault and block the Caspian Sea coast on the coast of Iran and are covered to the east with thick layers of loess.

In the field work that was carried out in May 2017, after determining the exact location of the sedimentary section, sampling was performed. Before sampling, aerated sedimentary layers are dug up and removed to reveal fresh deposits. Then, using the meter, the layers were divided into 10 cm intervals. 92 samples were prepared at 10 cm intervals from the sequence. Measurement of natural residue magnetic (NRM), by the model rotating magnetometer (JR-6A), and measurement of magnetic susceptibility by magnetic intensity measuring device, in the magnetometry laboratory of the Geological Survey of Iran.

Table 1 shows the measured values of the magnetic parameters. Due to the length of the table, only a few examples are given in the table. Since high magnetic susceptibility can indicate a greater concentration of magnetic minerals in the sample, it can be concluded that the paleosils of the sequence studied have more magnetic materials than the loesses, which are inside the soils. They can be the result of podogenesis processes. Because rising temperatures and humidity cause soil erosion processes and increase oxidation and thus increase the amount of magnetic materials, it can be concluded that in paleosoils with higher magnetic susceptibility, warm and humid climates dominate in the environment. Micromorphological studies of directional clay layers, Fe-Mn hydroxide, show that the palaeosoil of section 5 is moderate to well developed. As the climate changes to higher temperatures and higher humidity, weathering and pedogenesis also increase, leading to the development of a pedogenic oxidation environment as a result this produce the formation of tiny magnetic grains such as maghemite and magnetite in this oxidizer environment and thus increases the magnetic susceptibility. In Saadabad, the high amount of xlf along with the high percentage of xfd suggests that many of the ultra-fine maghemite and magentite grains may have been formed during pedogenesis under a long, humid, warm climate. The findings show that the different behaviors of magnetic susceptibility between the loess of the drier and wetter areas are mainly caused by their different pathogenic environments, which in turn are related to local topography and climatic conditions.

High levels of xlf and xfd indicate high precipitation during the formation of Paleosoils. Post-sedimentation processes may increase the amount of MS by producing new ferromagnetic minerals during the oxidation of wheathered soils, and may also reduce the amount of MS by reducing the processes. The clay material in which the soil is made is the main factor influencing the change in magnetic mineralogy and magnetic susceptibility. This study also shows that magnetic susceptibility is a complex parameter and its use as a precipitation control has certain limitations and conditions, and when the magnetic properties of the loesses are used for paleo climate reconstruction, more attention should be paid to topography, environment. Sediment and weather factors.

Magnetic susceptibility is one of the most important tools for monitoring the sediment composition during environmental studies. In this research, in order to reconstruct the Caspian Sea level changes, magnetic susceptibility variations were used during the studies of 5 sedimentary cores (K1, K3, K5, K7, N1), collected from bottom sediments of Gorgan Bay. Samples were analyzed for grain size, total organic matter, carbonate content and magnetic susceptibility (MS). The results showed a close relationship between particle size distribution and MS magnitude due to variation in terrestrial influx, which was caused by sea-level fluctuations in different times. This process increases with rising particle size and magnitude of MS simultaneously with sea level fall and decreases during sea-level rise. Moreover, no relationship between magnitude of MS and carbonate content was observed. It could be concluded that using magnetic susceptibility curves with other data, such as geological and historical data, could be suitable for the reconstruction of marine environments, especially in the near shore coastal area.

The high-Tc Y1-xNixBa2Cu3O7-δ samples doped by Ni for Y atom, with x=0, 0.002, 0.004, 0.006 and 0.01 were synthesized by the standard solid-state reaction method. The XRD diffraction of samples showed no impurity phase in all samples. Magnetic susceptibility of the samples under two different magnetic fields of 0.8 and 400 A/m was measured. The results showed that by increasing nickel element to an optimum value, the intragranular connection and flux pinning were improved.

In this research single phaseLa0.7(Sr 1-xBax)0.3MnO3(x =0, 0.1 , 0.2 , 0.3) nanomanganite with crystalline size of 18-28 nm have been prepared by sol gel method. The structural properties have been studied using X-ray diffraction spectra with its Rietveld analysis and scaning electron microscope images. The magnetic and elctrical properties have been investigated by measuring the ac magnetic susceptibility and resistivity in the presence of magnetic fields in the range of 0-20 kOe. The obtained results from ac magnetic susceptibility show that the Curie temperture of the samples are above room temperture. The results of resistivity show that the metal-insulator phase transition temperture of La0.7 Sr0.3 MnO3 and La0.7 (Sr0.3 Ba0.2) MnO3 compounds are below room temperture. The resistivity of the samples strongly decreases and their magnetoresistance almost linearly increases by incrasing the applied magnetic field at different tempertures. The value of magnetoresistance for La0.7 (Sr0.3 Ba0.2) MnO3 Ecompound is 10 % and 14 % at 275 K and 200 K, and for La0.7 Sr0.3 MnO3 Ecompound is 13 % and 27 % at 275 K and 100 K, respectively which are suitable for magnetic field sensing applications. The magneto-transport properties of La0.7 (Sr1-x Bax) MnO3 nanomanganite are described in terms of spin dependent scattering of charge carriers from grain boundaries and their spin dependent tunneling between grains.

Nanomagnetism is a branch of nanotechnology, which studies the magnetic properties of nanoparticles. Single-domain superparamagnetim, superferromagnetism and superspin glasses are different magnetic states which have been observed in a system of nanoparticles. Each of these magnetic states has unique features which determines the application range of magnetic nanoparticles assembly. Shell of nanoparticles is composed of canted spins while the core spins are almost regular. Study of nanoparticles system needs to explore and characterize several features, including different anisotropies, interactions between the particles, relaxation times, coercivity, remanent magnetization, saturation magnetization and etc. Researchers have made great efforts to characterize magnetic nanoparticles. Investigations in nanomagnetism field increases by developing the application range of nanoparticles in industry, medicine and daily life.

In this work, La0.6Sr0.4MnO3 manganite particles with nano and micro scales were prepared by Sol-gel and solid state reaction methods. The results from X-ray diffraction analysis by Fullprof software showed that the samples have been crystallized in the rhombohedral structure with (R-3C) space group. Investigation of magnetic properties showed that this compound belong to soft ferromagnetic materials and Curie temperature of the samples shifted to lower temperatures with particle size reduction. Calculation of the effective magnetic moment using Curie-Weiss model showed the magnetic moment reduction of the samples with particle size decreasing. Using magnetization versus field, magnetic saturation reduction, due to particle size decreasing, was observed. The observed behavior described with Core-shell model and the thickness of magnetic dead layer was estimated.

Dust is a significant environmental medium that can provide information about the level, distribution and fate of contaminants present in the surface environment. Dust could be an indicator of pollutants such as heavy metal in the atmosphere. Furthermore, the elemental composition and concentrations in dust reflects the characteristics of short and long term activities in the area. Atmospheric dust is investigated as an important source of heavy metals in urban and industrial areas. Heavy metals can accumulate in dust and disperse in large scale. Thus, in these areas dust contains considerable amount of heavy metals. Both dust and heavy metals may cause human health issues and adverse environmental effects. Various and conventional methods have been used to determine heavy metal contamination in soil, dust, water, and sediment. Almost all of these methods are based on chemical analysis and particularly acid digestion. In recent years, researchers have used magnetic susceptibility (MS) technique as an acceptable approach to identify pollution sources. Magnetic measurements are fast, cost-effective, non-destructive, sensitive and informative. Strong correlation between heavy metal concentration and magnetic susceptibility in dust can be used for fast assessment of heavy metals contamination and their spatial distribution. Studies have shown that magnetic susceptibility is a useful tool to identify industrial pollutants, traffic pollutants and other atmospheric pollutants.

Human activities in areas with a high rate of urbanization and industrialization growth have contributed to the increase of environmental pollution. Soils and sediments pollution is also significantly threatening human health and environmental quality. The main reasons of anthropogenic particulate pollution in urban areas have been industrial activities and vehicle emission among others. The magnetic susceptibility (χ) of soils results mainly from their magnetite and magnetite contents. Parts of the magnetic materials in the soil are inherited from soil parent material. Magnetic susceptibility could also be increased or decreased by biochemical and transformation processes. Water, organic matter and carbonates have very low magnetic susceptibility and; therefore, their existence in the soil greatly influence the soil overall magnetic susceptibility. Soil magnetic enhancement can be due to anthropogenic origin such as industrial and urban dusts containing magnetic particles. Magnetic particles, emitted from vehicular sources are accompanied with increasing metal concentrations, especially Cu, Pb, Cd and Zn as a result of paint, fuel additives, tires, and brake dust. Pollutants are transported through atmospheric pathways and deposited on the ground. Very little information exists about the relationship between soil properties and magnetic susceptibility, particularly calcareous soils which are abundant in Iran. Therefore, this study has been aimed to determine the magnetic susceptibility and its relationship with selected heavy metals and soil properties and to determine the correlation between the magnetic properties and heavy metal concentrations in surface soils of the Isfahan region, central Iran.

In this paper Sb2O3 nanoparticles are synthesized by solution method. The effect of these nanoparticles on the Bi-2223 superconductor properties has been investigated. The critical temperature, critical current density and activation energy were measured by the standard four-probe method. Magnetic properties of the samples were measured by using the AC magnetic susceptibility. The microstructure and morphology of samples have been studied by X-ray diffraction, scanning electron microscope and energy dispersive X-ray. The results of X-ray diffraction patterns show that the low amount of Sb2O3 and long annealing time enhance the fraction of Bi -2223 phase. Also the results show that the Sb2O3 nanoparticles do not change the phases and critical temperature of Bi-2223 superconductor, but by increasing the amount of Sb2O3 nanoparticles, the critical current density and the activation energy of the samples increase.

The study area is located 92 Km south-east of Torbat-e-Heydariyeh and 12 Km to the north of Shahrak village in Khaf-Dorouneh volcanic-plutonic belt. Mineralization was formed in fault zones where they cross the intermediate plutonic rocks. Propylitic alteration is widespread and is the dominant type in the area. Magnetite and Specularite with variation in the amount form major portion of mineralization zones. Other primary minerals are Quartz, Calcite, Pyrite, Chalcopyrite and Chlorite. Analysis of a few samples of mineralization for Au, Cu, Pb and Zn elements using the A.A.S method. The amount of copper is 0.2 percent and gold 44 ppb. Microthermometry study of fluid inclusions in Quartz indicated temperature ranges from 160˚C to more than 430˚C and relatively high salinity for mineralization zones. Thermometry study of fluid inclusions in Quartz-Chalcopyrite veins showed Temperatures between 160˚C - 203˚C and relatively high salinity for the solution. Minimum and maximum salinity that obtained were equal to 19 and 31 percent respectively in terms of NaCl. The closest compound system for fluid inclusions was determined H2O-NaCl-CaCl2 triple system. Considering high amount of magnetite and high value of magnetic susceptibility in mineralization, ground magnetic survey was carried out which resulted to the delineation of areas of covered mineralization. Interpretation of magnetic anomalies in profiles, was indicative of the continuation of surface mineralization and increase of magnetite with depth.

Manganites are considered as subbranches of condensed matter physics with a great wealth of physical mechanisms. In this investigation we have studied the structural, electrical and magnetic properties of a series of La1-xCaxMnO3 manganite with x=0.1, 0.2, …,0.5. We observed that the crystal structure of this manganite, with small dopping, at room temperature is orthorhombic and by increasing the amount of dopping, its structure changes towards tetragonal. Also, by increasing calcium dopping a metallic phase induction occurs at low temperature and also a metal-insulator transition occurs at the samples Curie temperature. By increasing the amount of dopping to 0.5 the metalic-insulator transition temperature and the Curie temperature of the samples both increase first and then decrease. We suggest a theoretical model with which we can interpret qualitatively many properties of manganites, such as their metal-insulator phase transition and their colossal magnetoresistance.

KC5 copper exploration prospect is located 80 Km to the northwest of Bardaskan and 4 Km to the Northeast of Dahaneh Siah copper mine in Khorasan Razavi. KC5 and Dahaneh Siah areas belong to Sabzevar geological Zone. Copper mineralization is observable mainly as secondary minerals such as Malachite and Chlorite which fills joints and fractures in a faulty contact at the boundary of the volcanic and Oriyan sedimentary (carbonaceous and tuff) rocks. High intensity ellipsoidal aeromagnetic anomaly overlies the boundary between the volcanic and carbonaceous rocks which follows old abandoned copper mines and extends to the KC5 prospect and Dahaneh Siyah area. Studies indicate the presence of magnetite up to maximum 5% in the volcanic rocks. Magnetic susceptibilities of the volcanic rocks in the KC5 west, KC5 east and Dahaneh Siyah show that this parameter is 2 times smaller in the first area than in the second and third. Magnetic anomalies of the two volcanic units in the KC5 east are similar but their amplitudes are lower than the anomalies produced by the same units in the KC5 west. Anomaly amplitudes of the Dahaneh Siyah volcanic are smaller than those produced by the same volcanic unit in the KC5 west and east. Lower magnetic susceptibilities of surface volcanic samples in the KC5 west and their higher amplitude anomalies in comparison with the anomalies from similar volcanic units in the KC5 east and Dahaneh Siyah implies that the source of the anomaly and main mineralization at KC5 west must be deep. Correlation of aeromagnetic anomaly with old abandoned copper mine (including the Dahaneh Siyah copper mine and the KC5 prospect area), uuper boundary of the volcanic and carbonaceous sediment and geochemical anomaly of the region are indications of the relation of main mineralization with aeromagnetic anomaly.

Magnetostriction and low field ac-susceptibility of polycrystalline Gd1-xPrxCo5 (x = 0, 0.1 and 0.5) alloys are measured in temperature region of 77-300 K. XRD patterns show that our samples are single phase. For x = 0 (GdCo5) there are no anomaly in temperature dependence of magnetostriction and ac-susceptibility curves. For x = 0.1 and 0.5 temperature dependence of ac-susceptibilities show easy-axes phase transitions. In the case of x = 0.1 sample, the easy-axes of magnetization changes from canted to axial (practically, hexagonal c-axis) direction as temperature increases, and ac-susceptibility of x = 0.5 sample shows two iterative transitions, first from basal to canted then canted to axial. Magnetostriction of Pr contained samples anomalously decreases at spin reorientation regions.