Curie Law Research Articles

Magnetic Properties of Gd-Doped Bi7Fe3Ti3O21 Aurivillius-Type Ceramics.

The magnetic properties of Aurivillius-phase Bi7Fe3Ti3O21 (BFT) and Bi7-xGdxFe3Ti3O21, where x = 0.2, 0.4, and 0.6 (BGFT), were investigated. Ceramic material undoped (BGF) and doped with Gd3+ ions were prepared by conventional solid-state reaction. In order to confirm that the obtained materials belong to Aurivillius structures, XRD tests were performed. The XRD results confirmed that both the undoped and the gadolinium-doped materials belong to the Aurivillius phases. The qualitative chemical composition of the obtained materials was confirmed based on EDS tests. The temperature dependences of magnetization and magnetic susceptibility were examined for the ceramic material both undoped and doped with Gd3+ ions. The measurements were taken in the temperature range from T = 10 K to T = 300 K. Using Curie's law, the value of the Curie constant was determined, and on its basis, the number of iron ions that take part in magnetic processes was calculated. The value of Curie constant C = 0.266 K, while the concentration of iron ions Fe3+, which influence the magnetic properties of the material, is equal 3.7 mol% (for BFT). Hysteresis loop measurements were also performed at temperatures of T = 10 K, T = 77 K, and T = 300 K. The dependence of magnetization on the magnetic field was described by the Brillouin function, and on its basis, the concentration of Fe3+ ions, which are involved in magnetic properties, was also calculated (3.4 mol% for BFT). Tests showed that the material is characterized by magnetic properties at low temperatures. At room temperature (RT), it has paramagnetic properties. It was also found that Gd3+ ions improve the magnetic properties of tested material.

Synthesis, crystal structure, and thermodynamic properties of two new selenate chlorides: M2Cu(SeO4)Cl2 with M = K and Rb

Two new selenate chlorides have been prepared for the first time by hydrothermal method. Their crystal structures have been determined. Both compounds are related to the chlorothionite mineral structure type but not isostructural to each other. K2Cu(SeO4)Cl2 crystallize in the orthorhombic system with the space group Pnma (#62) and unit cell parameters a = 7.7941(2)Å, b = 6.1297(2) Å, c = 16.6644(5) Å, V = 796.15(4) Å3, Z = 4 whereas Rb2Cu(SeO4)Cl2 crystallize in monoclinic system, P21/n (#14), and parameters a = 8.0701(3), b = 12.9474(5), c = 16.9354(7), β = 103.657(2)°, V = 1719.49(12) Å3, Z = 8. Potassium compound are isostructural to the related sulfate chloride, while rubidium selenate is differ from their sulfate analogue and from prototype compound K2Cu(SO4)Cl2. Both examined crystal structures feature copper ions in planar coordination CuO2Cl2 which form isolated magnetic chains along ⟨0 1 0⟩ direction in the structure. The study of M2Cu(SeO4)Cl2 was carried out in measurements of magnetic susceptibility χ(T) = M/B in the temperature range 2–350 K, magnetization M(B) at 2 K and specific heat Cp(T) in the range 2–120 K. At lowering temperature, the magnetic susceptibility exhibits no anomalies and follows by Curie law. An increase of the Cp(T) curve below 3 ÷ 8 K indicates the release of magnetic entropy. The study of thermodynamic properties unexpectedly shows that the investigated selenates M2Cu(SeO4)Cl2 (M = K and Rb) behave like paramagnets and the interaction between copper ions in the structural chains is negligible, opposite related sulfates demonstrating 1D magnetic behavior for Cu2+ magnetic ions.

Magnetism of single-doped paramagnetic tin clusters studied using temperature-dependent Stern-Gerlach experiments with enhanced sensitivity: impact of the diamagnetic ligand field and paramagnetic dopant.

In this work, the magnetic properties of tetrel clusters SnNTM, which are singly doped with transition metals (TM), are investigated. On the one hand, the number of tetrel atoms (N = 11, 12, 14 and 17 with TM = Mn) is varied; on the other hand, different transition metals (N = 14, TM = Cr, Mn, Fe) are studied. Magnetic deflection experiments under cryogenic conditions show that the variation of the number of tetrel atoms strongly changes the magnetic properties of the Mn-doped clusters. It is observed that Sn12Mn, Sn11Mn and Sn14Mn partially show super-atomic behaviour, while spin relaxation occurs in Sn17Mn. Magnetic deflection experiments at higher nozzle temperatures were carried out for the first time enhanced by a second parallel-aligned Stern-Gerlach magnet to achieve larger deflections. The resulting temperature-dependent one-sided deflections are quantitatively analysed using Curie's law and show that Sn17Mn possesses the highest magnetic moment of these clusters, followed by Sn12Mn and Sn11Mn. Sn14Mn shows the lowest magnetic moment. The replacement of Mn by Cr in Sn14Mn leads to a diamagnetic singlet, i.e., the magnetic moment of Cr in Sn14Cr is completely quenched. The replacement of Mn by Fe in turn leads to a paramagnetic species, whereby Sn14Fe is most likely present as a triplet. On this basis, the geometrical and electronic structures are analysed using quantum chemical calculations, indicating an arachno-type structure for Sn14Cr, Sn14Mn and Sn14Fe, which has already been predicted in the literature for Si14Cr. This is experimentally confirmed by deflection of molecular beams with an electric field under cryogenic conditions, suggesting that the arachno-type geometry is crucial for the overall stability of the transition-metal-doped tetrel clusters Sn14TM with TM = Cr, Mn, Fe.

On a Heuristic Point of View about the Generalization of Curie Law to Cosmic Higgs Fields with the Casimir Effect

On a Heuristic Point of View about the Generalization of Curie Law to Cosmic Higgs Fields with the Casimir Effect

The physical properties of Hastelloy® C-276TM and Hastelloy® C-276TM with Al2O3/Y2O3/MgO/LaMnO3 buffer layers down to cryogenic temperatures for applications in superconducting magnets

For many years, the Ni–Mo–Cr superalloy Hastelloy® C-276™ has been employed as a substrate material for depositing superconducting REBa2Cu3O7-x (RE - rare earth element) and MgB2 layers with various intermediate buffer layers. The resulting superconducting tapes are widely used in various industrial applications. However, the presence of various intermediate buffer layers between the substrate and the superconducting layer can influence the magnetic and thermal properties. At present, there is a dearth of significant data in literature concerning the impact of buffer layers. In this study, we provide data on the physical properties of a commercial Hastelloy® C-276™ tape with deposited Al2O3/Y2O3/MgO/LaMnO3 buffer layers, along with an electro-polished Hastelloy® C-276™ substrate. Physical properties such as magnetic susceptibility (dc) and specific heat, Cp, were measured from 5 to 300 K and the chemical composition was investigated. In low magnetic fields and relevant temperature range (5–200 K), the magnetization of a Hastelloy substrate demonstrates the Curie law, while Hastelloy with deposited buffer layers demonstrates Curie-Weiss law. At the magnetic field of 9 T and temperature 5 K, the resultant relative specific magnetization, compared to electro-polished Hastelloy, was lower by 16%. For heat capacity, Debye T3 law provides a good approximation from 22 to 48 K but the impact of buffer layers at 100 K was higher by 9.5%, compared to electro-polished Hastelloy, and decreases gradually with decreasing the temperature.

Response of the competitive balance model to the external field.

The competitive balance model was proposed as an extension of the structural balance theory, aiming to account for heterogeneities observed in real-world networks. In this model, different paradigms lead to form different friendship and enmity. As an example, friendship or enmity between countries can have a political or religious basis. The suggested Hamiltonian is symmetrical between paradigms. Our analyses show that a balanced state can be achieved if just one paradigm prevails in the network and the paradigm shift is possible only by imposing an external field. In this paper, we investigate the influence of the external field on the evolution of the network. We drive the mean-field solutions of the model and verify the accuracy of our analytical solutions by performing Monte-Carlo simulations. We observe that the external field breaks the symmetry of the system. The response of the system to this external field, contingent upon temperature, can be either paramagnetic or ferromagnetic. We observed a hysteresis behavior in the ferromagnetic regime. Once communities are formed based on a certain paradigm, then they resist change. We found that to avoid wasting energy we need to know the level of stochastic behavior in the network. Analogous to magnetic systems, we observe that susceptibility adheres to Curie's law.

Study of Crystal Structure and Magnetics Properties in the Normal State of Electron-Doped Eu<sub>2-</sub><i><sub>x</sub></i>Ce<i><sub>x</sub></i>Cu<sub>0.97</sub>Zn<sub>0.03</sub>O<sub>4+</sub><i><sub>α-δ</sub></i> in Overdoped Regime

The normal state of high-Tc superconducting cuprates is crucial to understanding of the mechanism in superconductivity. There are two main ways to remove superconductivity so that the sample is in a normal state, that is by applying a large magnetic field or adding impurities such as Zn to the sample. To investigate the crystal structure and magnetic properties in the normal state of electron-doped high-Tc cuprates in overdoped regime, Eu2-xCexCu0.97Zn0.03O4+α-δ (ECCZO) with x = 0.16, 0.17, 0.18, and 0.19 has been synthesized by the solid-state reaction method. The crystal structure and magnetic properties of the samples were characterized by XRD and SQUID measurements. The results of XRD measurements shows all samples have T’-structure and the values of lattice parameters a, CuO bond length, and crystallite size increased with increasing x. On other hand, the value of lattice parameters c decreased with increasing x, causing the expansion of the tetragonal unit cell in the horizontal direction. From susceptibility measurements, in the normal state with 3% of Zn impurity all samples have the paramagnetic behaviour. The magnetic parameters of these samples analysed by the Curie law. With increasing of Ce concentration, the C and the are increased. The increase in the magnetic parameters since the increasing in magnetic ordering.

Dielectric response in the antiferromagnetic phase of Fe1.10Te

Fe1.10Te was studied by scanning tunneling microscopy (STM) and dielectric response to elucidate the charge fluctuation. The cleaved a-b surface was clearly imaged by UHV-STM at T = 8.3 K. From the line profiles, each Fe site was thought to be equivalent suggesting no static charge order in the antiferromagnetic phase. The temperature dependence of the dielectric permittivity was obtained by measuring the complex impedance. The dielectric permittivity increased with decreasing temperature below the Neel temperature TN. The temperature dependence followed the Curie law, indicating the paraelectric state. It suggests charges fluctuate dynamically in the antiferromagnetic state. We conclude that the dynamical charge fluctuation cooperates with the antiferromagnetic order in Fe1.10Te.

Field-Induced Single-Ion Magnet Behavior in Nickel(II) Complexes with Functionalized 2,2':6'-2″-Terpyridine Derivatives: Preparation and Magneto-Structural Study.

Two mononuclear nickel(II) complexes of the formula [Ni(terpyCOOH)2](ClO4)2∙4H2O (1) and [Ni(terpyepy)2](ClO4)2 MeOH (2) [terpyCOOH = 4'-carboxyl-2,2':6',2″-terpyridine and terpyepy = 4'-[(2-pyridin-4-yl)ethynyl]-2,2':6',2″-terpyridine] have been prepared and their structures determined by single-crystal X-ray diffraction. Complexes 1 and 2 are mononuclear compounds, where the nickel(II) ions are six-coordinate by the six nitrogen atoms from two tridentate terpy moieties. The mean values of the equatorial Ni-N bond distances [2.11(1) and 2.12(1) Å for Ni(1) at 1 and 2, respectively, are somewhat longer than the axial ones [2.008(6) and 2.003(6) Å (1)/2.000(1) and 1.999(1) Å (2)]. The values of the shortest intermolecular nickel-nickel separation are 9.422(1) (1) and 8.901(1) Å (2). Variable-temperature (1.9-200 K) direct current (dc) magnetic susceptibility measurements on polycrystalline samples of 1 and 2 reveal a Curie law behavior in the high-temperature range, which corresponds to magnetically isolated spin triplets, the downturn of the χMT product at lower temperatures being due to zero-field splitting effects (D). Values of D equal to -6.0 (1) and -4.7 cm-1 (2) were obtained through the joint analysis of the magnetic susceptibility data and the field dependence of the magnetization. These results from magnetometry were supported by theoretical calculations. Alternating current (ac) magnetic susceptibility measurements of 1 and 2 in the temperature range 2.0-5.5 K show the occurrence of incipient out-phase signals under applied dc fields, a phenomenon that is characteristic of field-induced Single-Molecule Magnet (SMM) behavior, which herein concerns the 2 mononuclear nickel(II) complexes. This slow relaxation of the magnetization in 1 and 2 has its origin in the axial compression of the octahedral surrounding at their nickel(II) ions that leads to negative values of D. A combination of an Orbach and a direct mechanism accounts for the field-dependent relation phenomena in 1 and 2.

Enhanced Thermoelectric Performance by Resonant Doping and Embedded Magnetic Impurity

The thermoelectric energy-conversion efficiency is significantly enhanced by introducing magnetism. Doping $\mathrm{Cr}$ atoms in a ${\mathrm{Cu}}_{2}{\mathrm{Sn}\mathrm{S}}_{3}(\mathrm{CTS})$ matrix modifies the electron density of state (e-DOS) and causes a special electron-transport mechanism by localized impurity spin moments. The localized spin moments cause a spin-spin exchange interaction with the spin of itinerant electrons of the CTS matrix. This is clearly verified in M-T measurement, which deviated from Curie's law. The figure of merit (zT) of the magnetic nanocomposite was 8 times higher than that of pristine CTS by the synergetic effect of modifying e-DOS near the Fermi level and electron transport by localized spin moments.

The Magnetic Properties and Magnetocaloric Effect of Pr0.7Sr0.3MnO3 Thin Film Grown on SrTiO3 Substrate

The magnetic behaviors and magnetocaloric effect (MCE) of Pr0.7Sr0.3MnO3 (PSMO-7) film grown on a (001) SrTiO3 single-crystal substrate by a pulsed laser deposition (PLD) were studied in this paper. X-ray diffraction with a high resolution (HRXRD) measurement shows that PSMO-7 film is grown with a (001) single orientation. The magnetic properties and the MCE related to the ferromagnetic (FM) phase transition of the PSMO-7 film are investigated using the temperature dependence of magnetization M(T) and the magnetic field dependence of magnetization M(H). The M(T) data suggest that with decreasing temperatures, the PSMO-7 film goes through the transition from the paramagnetic (PM) state to the FM state at around the Curie temperature (TC). The TC (about 193 K) can be obtained by the linear fit of the Curie law. Magnetic hysteresis loop measurements show that the PSMO-7 film exhibits the FM feature at temperatures of 10, 100, and 150 K (low magnetic hysteresis can be found), while the film reveals the PM feature with the temperature increased up to 200 and/or 300 K. The research results of M(H) data are consistent with the M(T) data. Furthermore, the magnetic entropy change (-ΔSM) of the PSMO-7 film was studied. It was found that the maximum value of (-ΔSM) near TC reaches about 4.7 J/kg·K under the applied field change of 20 kOe, which is comparable to that of metal Gd (-ΔSM of 2.8 J/kg K under 10 kOe), indicating the potential applications of PSMO-7 film in the field of magnetic refrigeration.

Temperature dependences of paramagnetic response in oxidized spark plasma sintered carbon nanotubes: The way of understanding the local electronic structure

Electron paramagnetic resonance (EPR) spectroscopy was used to study an electronic structure of carbon nanotubes (CNTs) consolidated by spark plasma sintering and additionally oxidized in vapor of boiling nitric acid. Two components were distinguished in the EPR absorption spectra: narrow and broad lines with different g-factors. This testified to the different surrounding of paramagnetic centers associated with the lines. Temperature dependence of spin numbers, associated with the narrow line, transfers from Curie-Weiss law to Curie law with increasing temperature. EPR susceptibility, associated with the broad line, can be attributed to a paramagnetic matrix with superparamagnetic inclusions.

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.

Analysis of the nagnetic properties of core-shell iron oxide nanoparticles

We report on the magnetization of core-shells nanoparticles. Magnetic nanoparticles with a core of magnetite of 13 nm diameter covered with a shell of dopamine (1.1 nm thickness) are studied through vibrating sample magnetometer (VSM), Monte Carlo (MC) computer simulations, and analytical equations. All parameters involved in the theoretical analysis are experimentally determined, namely, the magnetic moment, temperature, magnetic field, core diameter, shell thickness, magnetic anisotropy, and particle concentration. The dependence of the magnetization with the magnetic field obtained through VSM and MC shows a 1% discrepancy in the magnetic saturation and up to 40% in the initial magnetic susceptibility. However, the dependence of the magnetization with the temperature obtained by MC indicates that the MNPs obey the Curie law above a critical temperature of 100 K, and dipolar interactions play an important role in the interval 20 < T < 100 K. That critical temperature is very close to the blocking temperature measured following the zero-field-cooled and zero-cooled protocols, where the dipolar interactions between MNPs become significant. Further analysis shows a Langevin-like behavior for both experimental and theoretical magnetizations.

Dynamical mean-field theory study of a ferromagnetic CrI3 monolayer

We have employed one of the well-known many-body techniques, density functional theory plus dynamical mean-field theory (DFT + DMFT), to investigate the electronic structure of ferromagnetic monolayer CrI3 as a function of temperature and hole-doping concentration. The computed magnetic susceptibility follows the Curie's law, indicating that the ferromagnetism of monolayer CrI3 originates from localized magnetic moments of Cr atoms rather than Stoner-type itinerant ones. The DFT + DMFT calculations show a different coherent temperature for each spin component, demonstrating apparent strong spin-dependent electronic correlation effects in monolayer CrI3. Furthermore, we have explored the doping-dependent electronic structure of monolayer CrI3 and found that its electronic and magnetic properties are easily tunable by the hole-doping.

The heterospin cobalt complexes: peculiarities of high-resolution NMR spectra

The high-resolution 1H and 13C NMR spectra (CHCl3 solution) of sterically non-rigid heterospin complexes CoL2, CoL2-dipy, and CoL2-phen (where L is 4-(3′,3′,3′-trifluoro-2′-oxopropylidene)-2,2,5,5-tetramethyl-3-imidazolidine-1-oxyl) have been studied. The specific of the NMR phenomenon in paramagnetic systems is briefly analyzed. It is shown that the NMR spectra modified by hyperfine coupling can be successfully employed for investigation of the complexation processes. In accordance with the common protocols, the 1H and 13C NMR signals are assigned using the information on 13С – 1Н spin-spin coupling. In addition, the preliminarily recorded 1H and 13C NMR spectra of radical L are also used in the work.The temperature dependences of 1H and 13C paramagnetic shifts in the complexes under study have been obtained. A fundamental feature of these dependences is that they obey to the Curie law in a fairly wide temperature range (up to 100 °C). This observation can be used to control intramolecular processes of sterically nonrigid heterosystems in solutions.

Magnetic dipolar correlations in sillenite-structure bismuth ferrite: magnetic and Mössbauer effect studies

Results of the magnetic and Mössbauer effect studies of the polycrystalline Bi25FeO39 sillenite-structure bismuth ferrite are reported. A deviation of the magnetic susceptibility temperature dependence below 50 K from the Curie law is found that we relate to an onset of antiferromagnetic correlations due to the magnetic dipole-dipole interaction. The value of the Néel temperature less than 0.5 K is estimated. Mössbauer spectrum is represented by a single Lorentz-shape line down to 5 K that experiences significant broadening on cooling. Possible mechanisms of this broadening are discussed.

Unusual slow magnetic relaxation in a mononuclear copper(II) complex.

A hexacoordinate Cu(II) complex with the {CuO4O'N} donor set shows an intermolecular π-π stacking owing to which a 1D-chain structure is formed. The DC magnetic data at low temperature are consistent with the Curie law. The AC susceptibility shows a field supported slow magnetic relaxation that survives up to 7 K. The relaxation time at T = 2.0 K and BDC = 0.2 T is τ = 0.23 ms and it increases at BDC = 0.6 T to τ = 2.9 ms.

Are radicals responsible for the variable deuterium enrichments in chondritic insoluble organic material?

The insoluble organic material (IOM) in primitive chondritic meteorites is very enriched in D (up to δD ≈ 3500‰ in bulk). Based largely on a series of electron paramagnetic resonance (EPR) studies of IOM from three meteorites (Orgueil, Murchison and Tagish Lake), it has been suggested that these enrichments are the result of exchange with H2D+ in the solar nebula and that exchange with radicals in the IOM was particularly facile so that they are enormously enriched in D (δD ≥ 95000‰). To try to test whether radicals are largely responsible for the D enrichments in IOM, we have used EPR to measure the radical concentrations (spins/g) and g-factors of 18 IOM separates from C1-2 chondrites of varying petrologic type and chemical group that have a much wider range of H isotopic compositions (δD ≈ 600–3500‰) than in previous studies. We confirm the previous studies findings that IOM exhibits non-Curie law behavior and that it does not completely saturate even at microwave excitation powers of 200 mW. We also have obtained similar g-factor values. However, our IOM samples typically exhibit a lower and more limited range of spin concentrations, and smaller deviations from Curie law behavior than in previous studies. Nor do we observe correlations between bulk δD and either spins/g or non-Curie law behavior that would be expected if exchange between H2D+ and radicals, as previously proposed, was the cause of the D-enrichments in IOM. Indeed, in general the radical concentrations and the degree of non-Curie law behavior do not seem to correlate with any of the measured IOM properties, with chondrite group or parent body history (e.g., degree of aqueous alteration). The only exceptions are the IOM in four Tagish Lake lithologies whose spin concentrations increase with increasing degree of thermal processing as indicated by decreasing H/C and δD, and increasing aromaticity.

Decompose quantitative susceptibility mapping (QSM) to sub-voxel diamagnetic and paramagnetic components based on gradient-echo MRI data

PurposeA method named DECOMPOSE-QSM is developed to decompose bulk susceptibility measured with QSM into sub-voxel paramagnetic and diamagnetic components based on a three-pool complex signal model. MethodsMulti-echo gradient echo signal is modeled as a summation of three weighted exponentials corresponding to three types of susceptibility sources: reference susceptibility, diamagnetic and paramagnetic susceptibility relative to the reference. Paramagnetic component susceptibility (PCS) and diamagnetic component susceptibility (DCS) maps are constructed to represent the sub-voxel compartments by solving for linear and nonlinear parameters in the model. ResultsNumerical forward simulation and phantom validation confirmed the ability of DECOMPOSE-QSM to separate the mixture of paramagnetic and diamagnetic components. The PCS obtained from temperature-variant brainstem imaging follows the Curie's Law, which further validated the model and the solver. Initial in vivo investigation of human brain images showed the ability to extract sub-voxel PCS and DCS sources that produce visually enhanced contrast between brain structures comparing to threshold QSM.