Curie Law Research Articles

Coupling of ethanolamine ammonia-lyase protein and solvent dynamics characterized by the temperature-dependence of EPR spin probe mobility and dielectric permittivity.

Electron paramagnetic resonance (EPR) spectroscopy is used to address the remarkable persistence of the native Arrhenius dependence of the 2-aminopropanol substrate radical rearrangement reaction in B12-dependent ethanolamine ammonia-lyase (EAL) from Salmonella typhimurium from physiological to cryogenic (220 K) temperatures. Two-component TEMPOL spin probe mobility in the presence of 10 mM (0.08% v/v) 2-aminopropanol over 200-265 K demonstrates characteristic concentric aqueous-cosolvent mesodomain and protein-associated domain (PAD, hydration layer) solvent phases around EAL in the frozen solution. The mesodomain formed by the relatively small amount of 2-aminopropanol is highly confined, as shown by an elevated temperature for the order-disorder transition (ODT) in the PAD (230-235 K) and large activation energy for TEMPOL rotation. Addition of 2% v/v dimethylsulfoxide expands the mesodomain, partially relieves PAD confinement, and leads to an ODT at 205-210 K. The ODT is also manifested as a deviation of the temperature-dependence of the EPR amplitude of cob(II)alamin and the substrate radical, bound in the enzyme active site, from Curie law behavior. This is attributed to an increase in sample dielectric permittivity above the ODT at the microwave frequency of 9.5 GHz. The relatively high frequency dielectric response indicates an origin in coupled protein surface group-water fluctuations of the Johari-Goldstein β type that span spatial scales of ∼0.1-10 Å on temporal scales of 10-10-10-7 s. The orthogonal EPR spin probe rotational mobility and solvent dielectric measurements characterize features of EAL protein-solvent dynamical coupling and reveal that excess substrate acts as a fluidizing cryosolvent to enable native enzyme reactivity at cryogenic temperatures.

Mono- and Binuclear Copper(II) and Nickel(II) Complexes with the 3,6-Bis(picolylamino)-1,2,4,5-Tetrazine Ligand.

Four new compounds of formulas [Cu(hfac)2(L)] (1), [Ni(hfac)2(L)] (2), [{Cu(hfac)2}2(µ-L)]·2CH3OH (3) and [{Ni(hfac)2}2(µ-L)]·2CH3CN (4) [Hhfac = hexafluoroacetylacetone and L = 3,6-bis(picolylamino)-1,2,4,5-tetrazine] have been prepared and their structures determined by X-ray diffraction on single crystals. Compounds 1 and 2 are isostructural mononuclear complexes where the metal ions [copper(II) (1) and nickel(II) (2)] are six-coordinated in distorted octahedral MN2O4 surroundings which are built by two bidentate hfac ligands plus another bidentate L molecule. This last ligand coordinates to the metal ions through the nitrogen atoms of the picolylamine fragment. Compounds 3 and 4 are centrosymmetric homodinuclear compounds where two bidentate hfac units are the bidentate capping ligands at each metal center and a bis-bidentate L molecule acts as a bridge. The values of the intramolecular metal···metal separation are 7.97 (3) and 7.82 Å (4). Static (dc) magnetic susceptibility measurements were carried out for polycrystalline samples 1–4 in the temperature range 1.9–300 K. Curie law behaviors were observed for 1 and 2, the downturn of χMT in the low temperature region for 2 being due to the zero-field splitting of the nickel(II) ion. Very weak [J = −0.247(2) cm−1] and relatively weak intramolecular antiferromagnetic interactions [J = −4.86(2) cm−1] occurred in 3 and 4, respectively (the spin Hamiltonian being defined as H = −JS1·S2). Simple symmetry considerations about the overlap between the magnetic orbitals across the extended bis-bidentate L bridge in 3 and 4 account for their magnetic properties.

Universal thermodynamics in the Kitaev fractional liquid

In the Kitaev honeycomb model, the quantum spin fractionalizes into itinerant Majorana and gauge flux spontaneously upon cooling, leading to rich experimental ramifications at finite temperature and an upsurge of research interest. In this work, we employ the exponential tensor renormalization group approach to explore the Kitaev model under various perturbations, including the external fields, Heisenberg, and the off-diagonal couplings that are common in the Kitaev materials. Through large-scale manybody calculations, we find a Kitaev fractional liquid at intermediate temperature that is robust against perturbations. The fractional liquid exhibits universal thermodynamic behaviors, including the fractional thermal entropy, metallic specific heat, and an intermediate-temperature Curie law of magnetic susceptibility. The emergent universal susceptibility behavior, with a modified Curie constant, can be ascribed to the strongly fluctuating $\mathbb{Z}_2$ fluxes as well as the extremely short-ranged and bond-directional spin correlations. With this insight, we revisit the susceptibility measurements of Na$_2$IrO$_3$ and $\alpha$-RuCl$_3$, and find evident signatures of finite-temperature fractionalization and ferromagnetic Kitaev couplings. Moreover, the peculiar spin correlation in the fractional liquid corresponds to a stripy structure factor which rotates in the extended Brillouin zone as the spin component changes. Therefore, our findings encourage future experimental exploration of fractional liquid in the Kitaev materials by thermodynamic measurements and spin-resolved structure factor probes.

Thermodynamics and Screening in the Ising–Kondo Model

A simplification of the symmetric single‐impurity Kondo model is introduced and studied. In the Ising–Kondo model, host electrons scatter off a single magnetic impurity at the origin whose spin orientation is dynamically conserved. This reduces the problem to potential scattering of spinless fermions that can be solved exactly using the equation‐of‐motion technique. The Ising–Kondo model provides an example for static screening. At low temperatures, the thermodynamics at finite magnetic fields resembles that of a free spin‐1/2 in a reduced external field. Alternatively, the Curie law is interpreted in terms of an antiferromagnetically screened effective spin. The spin correlations decay algebraically to zero in the ground state and display commensurate Friedel oscillations. In contrast to the symmetric Kondo model, the impurity spin is not completely screened, i.e., the screening cloud contains less than a spin‐1/2 electron. At finite temperatures and weak interactions, the spin correlations decay to zero exponentially with correlation length ξ(T) = 1/(2πT).

Decreasing iron susceptibility with temperature in quantitative susceptibility mapping: A phantom study

To clarify the temperature dependence of susceptibility estimated by quantitative susceptibility mapping (QSM) analysis, we investigated the relationship between temperature and susceptibility using a cylinder phantom with varying temperatures. Six solutions with various concentrations of superparamagnetic iron oxide (SPIO) nanoparticles were employed. These tubes were placed in a cylinder phantom and surrounded with water. The temperature of the circulated water was adjusted to change the temperature in the cylinder phantom from 25.8 °C to 42.5 °C. The cylinder phantom was scanned via a three-dimensional multiple spoiled gradient-echo sequence for R2* and QSM analyses with varying temperatures. The relationships between temperature, susceptibility, and R2* values were determined. Moreover, the temperature coefficients of susceptibility (χ-Tc) and (R2*-Tc) were calculated at each concentration and the linearities in these indices against each SPIO concentration were validated. Significant inverse correlations were found between temperature, susceptibility, and R2* values at each SPIO concentration due to the decrease in paramagnetic iron susceptibility that occurred with increasing temperature based on Curie's law. Moreover, although there were significant correlations between the susceptibility and R2* values at any temperature, the slopes of the regression lines grew in height with greater temperatures. The percentage of difference per Celsius degree in susceptibility in any SPIO concentration was lower than the corresponding finding among the R2* results. There were strong linearities between the SPIO concentration, χ-Tc (r = −0.994; p < 0.001), and R2*-Tc (r = −0.998; p < 0.001). The χ-Tc and R2*-Tc outcomes in a particular voxel varied considerably with the iron contents. Although there was an inverse correlation noted between temperature and susceptibility, the susceptibility analysis showed smaller temperature dependence relative to the R2* analysis. QSM analysis might be a more suitable option for magnetic resonance-based iron quantification in comparison with R2* relaxometry.

Localization of conduction electrons in hydrothermally reduced graphene oxide: electron paramagnetic resonance studies

Partially reduced graphene oxide (prGO) obtained by hydrothermal reduction was studied by electron paramagnetic resonance (EPR) spectroscopy in the temperature range 4.2–300 K. The EPR absorption is accompanied by nonresonant microwave absorption due to dielectric and conduction losses in prGO. This additional absorption is taken into account to determine correctly intensities of EPR spectra. The EPR spectra of prGO consist of the broad and narrow components. Above 100 K, the intensity of the broad component exhibits the Curie-Weiss behavior, but below 100 K it follows the Curie law revealing the disappearance of antiferromagnetic correlations. For the first time, the unusually strong increase of the narrow EPR signal intensity with lowering temperature is observed. This effect is explained by the Anderson localization of conduction electrons in the defected crystalline structure of prGO. Due to low spin density, the localized electrons become isolated and their magnetic susceptibility follows the Curie law with the temperature-dependent number of magnetic moments. Effects of adsorption of atmospheric gases on the observed properties are analyzed.

Magnetic sensitivity of the microwave cryogenic sapphire oscillator

The Cryogenic Sapphire Oscillator (CSO) is today recognized for its unprecedented frequency stability, mainly coming from the exceptional physical properties of its resonator made in a high-quality sapphire crystal. With these instruments, the fractional frequency measurement resolution, currently of the order of 10−16, is such that it is possible to detect very small phenomena such as residual resonator environmental sensitivities. Thus, we highlighted an unexpected magnetic sensitivity of the CSO at low magnetic fields. The fractional frequency sensitivity has been preliminarily evaluated to be 10−13/G, making this phenomenon a potential cause of frequency stability limitations. In this paper, we report the experimental data related to the magnetic sensitivity of the quasi-transverse magnetic Whispering Gallery (WGH) modes excited in sapphire crystals differing from their paramagnetic contaminant concentration. The magnetic behavior of the WGH modes does not follow the expected theory combining the Curie law and the Zeeman effect affecting the electron spin resonance of the paramagnetic ions present in the crystal.

On the Possibility of Studying Ferrofluids by a Nuclear Magnetic Magnetometer with a Flowing Sample

In this paper, we consider a new method that employs a highly sensitive nuclear magnetic magnetometer with flowing water to determine the magnetic susceptibility and Curie constant of magnetic fluids with an error no greater than 1.0%. The Curie law was shown to be fulfilled in the temperature range of 283–323 K, in which ferrofluidic cells are used. A further increase in the temperature of the ferromagnetic fluid leads to an insignificant change in the Curie constant. The results of experimental studies are presented.

Universal Curie constant and pyroelectricity in doped ferroelectric HfO2 thin films

Abstract Pyroelectric coefficients are measured for Si, Sr, La, Al, and Gd doped HfO2 thin films as well as the solid-solution Hf0.5Zr0.5O2 composition from 280 to 440 K. Pyroelectric currents show sensitivity to the dopant used to stabilize ferroelectricity in HfO2. Large pyroelectric coefficients up to 70 μC cm−2 K−1 were measured in films with the largest remanent polarization magnitudes, La-doped HfO2 and Hf0.5Zr0.5O2. A temperature-driven ferroelectric to antiferroelectric-like transition influences the pyroelectric coefficient and is found only in Si-doped HfO2 thin films. The transition is shown to produce a decrease in the Curie constant with temperature and thus deviates from the Curie law, although most ferroelectric films reported here obey the Curie law. Independent measurements of the remanent polarization, relative permittivity, and pyroelectric coefficient are used to extract the Curie constants of the thin films. The fundamental thermodynamic relationship between the dielectric, ferroelectric, and pyroelectric properties of ferroelectric HfO2 thin films are established based on Landau theory with a universal Curie constant of 5.8 × 10−7 ± 0.46 × 10−7 K C V−1 m−1 (Landau coefficient, α0 = 1.72 × 106 ± 0.138 × 106 V m K−1 C−1) for ferroelectric HfO2 independent of doping concentration and dopant type. An electro-thermal coupling factor of 1.9 × 10−3 and a voltage responsivity figure of merit of 0.085 m2/C illustrate the promising potential of ferroelectric HfO2 thin films for use in embedded energy harvesting and infrared sensing circuits.

On the Possibility of Determining the Curie Constant and Magnetic Susceptibility of Colloidal Solutions by Method of Nuclear Magnetic Resonance

A new universal technique was suggested to determine the Curie constant С and magnetic susceptibility of colloidal solutions placed in hermetically sealed vessels (for instance, ferrofluid cells) with an error of no more than 1.0%. Experimental research demonstrated that in the temperature range Т from 283 to 323 K, in which ferrofluid cells are used, the Curie law is fulfilled. It was established that increase in temperature Т of the colloidal solution from 324 to 363 K in a ferrofluid cell leads to an insignificant increase in С, which needs to be taken into account when conducting experiments using these cells. Results of research on colloidal solutions are presented in the paper.

NMR Studies of the Dynamics of 1D $$^3\hbox {He}$$ in $$^4\hbox {He}$$ Plated MCM-41

Pulsed NMR techniques have been used to study the dynamics of $$^3\hbox {He}$$ confined to the interior of the hexagonal nanochannels of MCM-41 for which the walls were coated with a monolayer of $$^4\hbox {He}$$ as determined by isotherm measurements. The $$^3\hbox {He}$$ was added afterward to form a 1D $$^3\hbox {He}$$ line density of about 0.1 $$\hbox {A}^{-1}$$ , corresponding to a Fermi temperature of $$T_{\mathrm{F}} \sim$$ 120 mK. A distinct and appreciable departure from the Curie law was observed for the nuclear spin magnetization below 0.5 K. The temperature dependence of the nuclear spin–lattice relaxation times, $$T_1$$ , for temperatures $$0.05<T<2.5$$ K, followed the expected linear behavior at low temperatures, and a peak was observed at $$T\sim 2T_{\mathrm{F}}$$ consistent with the Luttinger liquid theory as predicted by Polini et al. (Phys Rev Lett 98:266403, 2007). The observed temperature dependence of the nuclear spin–spin relaxation times, $$T_2$$ , differed considerably from that observed for $$T_1$$ , with a minimum at $$T= 0.8$$ K, similar to the tendency reported by Matsushita and colleagues.

Electron spin resonance, dynamic Jahn-Teller effect, and electric transport mechanism in Na-doped type II silicon clathrates

Silicon clathrates are Si-cage-based structures capable of hosting other atoms, such as sodium, in their Si-polyhedron cages. Electron spin resonance (ESR) can provide information on the electronic structure of localized or delocalized electrons in cage-like type II silicon clathrates of the form NaxSi136 (0<x≤ 24). The ESR lines observed at low temperatures are classified into four distinct groups ascribed to (1) an isolated single-Na-containing cage, (2) a pair of single-Na-containing cages or clusters composed of more than two single-Na-containing cages, (3) an electron localized around a silicon deficit with dangling bonds, and (4) a conduction electron. The spin-Hamiltonian parameters for the Na atom of group 1 can be explained by the combination of an off-center model and the dynamic Jahn-Teller effect for the single-Na-containing Si polyhedron. The Na content, x, dependence of the ESR signal of group 1 can be explained by the statistical formation probability of the isolated single-Na-containing cage in type II silicon clathrates. Deviation of the ESR signals of groups 1–3 from Curie's law as temperature increases from 110 to 500 K indicates the transition of bound electrons to delocalized states in type II silicon clathrates. The higher transition temperatures of approximately 170 K for the ESR signals of groups 1 and 2 and approximately 300 K for the ESR signals of group 3 correspond to large activation energies of approximately 0.12 eV and approximately 0.35 eV, respectively, from the electron-localized states to the conduction band.

Effect of Compensation on Low-Temperature Spin Ordering in Ge:As Semiconductor Near the Insulator–Metal Phase Transition

An electron-spin resonance technique has been used to examine the influence exerted by the degree of compensation on spin effects in a set of nonmagnetic Ge:As semiconductor samples in the vicinity of the insulator–metal phase transition at temperatures 2 K ≤ T ≤ 80 K. It was found that the behavior of the paramagnetic susceptibility, specific to the Pauli paramagnetism and manifested in the spin density resonance, is drawn deep into the insulator state and is observed up to rather large degrees of compensation K ≈ 0.7 at temperature 20 K ≥ T ≥ 5–10 K. Outside this temperature range, both the quantities rapidly grow with increasing compensation and their behavior approaches the Curie law characteristic of the strong insulator state. The reason for this behavior is that the degeneracy is lifted at high temperatures and, at low temperatures, electron states are localized at the Fermi level as a result of the Coulomb blockade by compensating acceptors of the most closely lying donor states and the resulting formation of a narrow Coulomb band in the metallized impurity band. At temperature T ≥ 5–10 K, the gap is blurred by thermal excitations and has no effect on the manifestation of the Pauli paramagnetism. The behavior of the line width of the electron-spin resonance is determined by the scattering on quasi-stationary electric dipoles created by the Coulomb blockade at low temperatures and by the scattering on phonons at high temperatures. The behavior of the g-factor is qualitatively correlated with the specific features of the paramagnetic susceptibility and spin density: with decreasing temperature it weakly grows in the range of the Pauli paramagnetism and then rapidly increases in the range in which the Coulomb blockade is manifested and a transition occurs to the Curie law. By an analogy with ferromagnetic materials in which such a fast increase in the g-factor is observed, the possibility of a compensation caused ferromagnetic coupling of spins localized on donors. The microscopic model of such a coupling is discussed.

In situ Electron paramagnetic resonance spectroelectrochemical study of graphene-based supercapacitors: Comparison between chemically reduced graphene oxide and nitrogen-doped reduced graphene oxide

An in situ electrochemical electron paramagnetic resonance (EPR) spectroscopic study of N-doped reduced graphene oxide (N-rGO) is reported with the aim of understanding the properties of this material when employed as an electrical double-layer capacitor. N-rGO shows a capacitance of 100 F g−1 in 6 M KOH, which is twice that found for reduced graphene oxide (rGO). The temperature dependence of the rGO EPR signal revealed two different components: a narrow component, following the Curie law, was related to defects; and a broad curve with a stronger Pauli law component was attributed to the spin interaction between mobile electrons and localised π electrons trapped at a more extended aromatic structure. The N-rGO sample presented broader EPR signals, indicative of additional contributions to the resonance width. In situ EPR electrochemical spectroscopy was applied to both samples to relate changes in unpaired electron density to the enhanced capacitance. The narrow and broad components increased and diminished reversibly with potential. The potential-dependent narrow feature was related to the generated radical species from corresponding functional groups: e.g. O- and N-centred radicals. Improved capacitance seen for the N-modified basal graphene planes can be accordingly suggested to underlie the enhanced capacitance of N-rGO in basic electrolytes.

The Impurity Magnetic Susceptibility of Semiconductors in the Case of Direct Exchange Interaction in the Ising Model

The numerical simulation was applied to study the temperature dependence of the impurity magnetic susceptibility. The direct exchange interaction of the impurity magnetic moments randomly distributed in space was considered within the Ising model. When the temperature in a system decreases, the magnetic susceptibility behavior in this system ceases to comply with the Curie law, which is associated with the formation of a spin glass phase. It is shown that the expression of the preexponential factor in the formula for the direct exchange interaction considerably influences the temperature dependence of the magnetic susceptibility only in the case of ferromagnetic exchange.

Magnetic response of bovine spleen

Abstract Bovine spleen has been used as a sample for deep magnetochemical investigation. Temperature dependence of the magnetic susceptibility and field dependence of the magnetization reveal a paramagnetic behaviour that violates the Curie law. The zero-field cooled magnetization and field cooled magnetization experiments show the bifurcation point at ca TC = 20 K and the blocking temperature TB = 10 K confirming a dominating portion of ferritin along with the organic tissue. There is a remnant magnetization at temperature below 20 K and the search for the magnetic hysteresis was positive.

Lambda (λ) Transition in the Heat Capacity by Finite Block Spin Phenomenology

We explain the lambda (λ) transition in the heat capacity in terms of spin freezing on the basis of finite-sized block spin concepts. Thus, the spin-glass phase or the antiferromagnetic/paramagnetic phase near the Neel temperature may be considered as a short-range ordering of the block spins comprised of many random spins with respective majority spin directions. Using the Curie law for the block spins, we obtain the λ-type heat capacity in the lower and the higher temperature approximations of the Brillouin function. The theoretical heat capacity gives a good fit to the experimental data.

Magnetic and Magnetotransport Characteristics of Cr-Substituted Ni55Mn34Sn11 Thin Films Grown by Magnetron Sputtering

Highly oriented Cr-substituted Ni55Mn34Sn11 Heusler thin films having thickness ~ 400 nm were deposited by Ultrahigh vacuum dc magnetron sputtering on MgO (100) substrates. At room temperature, the films exhibit a mixture of dominant L21 cubic austenite phase, as revealed by the intense (002) and (004) peaks, along with small fraction of the orthorhombic–martensitic phase. Surface morphology of the thin films showed distribution of Cr-rich and Cr-deficit regions together with patterned and aligned magnetic domains, thus bringing out the inherent room temperature ferromagnetism of the film. At temperatures above the Curie temperature, TC ~ 321 K, the magnetic behaviour of the films is seen to follow the Curie law rather than the Curie–Weiss law. Ferromagnetic to antiferromagnetic transition appears at TN ~ 247 K, which gives rise to exchange bias at low temperatures due to the coexistence of the two magnetic orders. This phase coexistence also leads to the formation of a spin glass state deep into the martensitic region. The film exhibits metal-like nature at high temperature and semiconductor-like behaviour with the lowering of temperature. A reentrant metallic state is observed at T ≤ 38 K during cooling that persists up to ≤ 62 K in warming cycle. The hysteresis in the ρ–T curve spread over a very wide temperature range confirms the magnetic phase coexistence in the martensitic state in the present thin films. The magnetoresistance (MR) first increases (2.4% at 300 K and H = 50 kOe) with temperature and maximizes to around ~ 3.25% at T = 150 K and then starts decreasing. Its value in the glassy state is very small. This shows that a magnetic liquid like state is more conducive to larger MR.

X-ray diffraction and magnetic properties of vanadium dioxide VO2±X solid solutions V1-XFeXO2

The article considers the results of vanadium dioxide VO2±X study (within the homogeneity range) and solid solutions V1-XFeXO2, obtained by X-ray diffraction and the Faraday method. The temperature dependences of the magnetic susceptibility samples are presented, and it follows that dependence χ (T) character in the temperature range from 100 К up to 250 К is close to Curie law for paramagnetic in the area of the phase transition at temperature Tmp ∼ 340 К, and there is an abrupt change in χ. It is considered that the magnetic properties of vanadium dioxide vary both with the change in the oxygen content in the samples and with the doping of vanadium dioxide with iron. It was established that vanadium dioxide VO2±X and solid solutions V1-XFeXO2 are paramagnetic both in the semiconductor and metallic states.

Примесная магнитная восприимчивость полупроводников в случае прямого обменного взаимодействия в модели Изинга

The dependence of the impurity magnetic susceptibility on temperature was studied by numerical simulation. The direct exchange interaction of magnetic moments of randomly distributed impurities was considered within the Ising model. The dependence of the magnetic susceptibility in such a system deviates from the Curie law at low temperature, which is associated with the formation of a spin glass phase. It is shown that the pre-exponential factor of the direct exchange interaction significantly influences on the temperature dependence of the magnetic susceptibility only in the case of ferromagnetic exchange.