Temperature Dependence Of Paramagnetic Susceptibility Research Articles

Visualization and analysis of magnetothermal convection of paramagnetic liquid in the Rayleigh-Benard model

We examined the heat transfer of magnetothermal convection in a Rayleigh-Benard model (height 9.2 mm, vessel diameter 20 mm, aspect ratio 2.17). The working fluid was an aqueous gadolinium nitrate solution of 0.15 mol/kg ($\mathrm{pH}=4.52$ at 305.5 K, paramagnetic substance). Not only the magnetic body force but also the temperature dependence of paramagnetic susceptibility according to Curie's law provides the driving body force of convection and exerts a decisive influence over the heat transfer performance. The visual observation of the isothermal contour of convection was realized by the addition of a thermochromic liquid crystal (TLC). Using a large upward magnetic body force, i.e., $(\stackrel{P\vec}{b}\ifmmode\cdot\else\textperiodcentered\fi{}\stackrel{P\vec}{\ensuremath{\nabla}})\phantom{\rule{0.16em}{0ex}}{b}_{z}=83.31\phantom{\rule{0.16em}{0ex}}{\mathrm{T}}^{2}/\mathrm{m}$ at the vessel center, we succeeded in visualizing the horizontal isothermal illuminant of the TLC, which revealed the realization of a quasiweightless condition in the Rayleigh-Benard model. The heat transfer on convection was analyzed by the method of Churchill and Ozoe. Its performance was enhanced by the downward magnetic body force and was suppressed by the upward magnetic body force, as compared with Rayleigh-Benard convection. The convective flows in the experiment ($\mathrm{Prandtl}\phantom{\rule{0.16em}{0ex}}\mathrm{number}=5.17$, $\mathrm{Ra}=1.53\ifmmode\times\else\texttimes\fi{}1{0}^{5}$, aspect ratio 2.0) were numerically simulated by three-dimensional computation. All the experimental and numerical results were arranged by Rayleigh number (Ra) and Nusselt number (Nu). In addition, we introduced the magnetic Rayleigh number (${\mathrm{Ra}}_{\mathrm{m}}$) instead of Ra. The results of Nu plotted versus the ${\mathrm{Ra}}_{\mathrm{m}}$ were closely distributed in the vicinity of the Silveston curve. This relationship reveals that the heat transfer on magnetothermal convection is controlled by the use of ${\mathrm{Ra}}_{\mathrm{m}}$.

CuIIand CuICoordination Complexes Involving Two Tetrathiafulvalene-1,3-benzothiazole Hybrid Ligands and Their Radical Cation Salts

Preparations, crystal structure analyses, and magnetic property investigations on a new Cu(II)(hfac)2 complex coordinated with two TTF-CH═CH-BTA ligands, where hfac is hexafluoroacetylacetonate, TTF is tetrathiafulvalene, and BTA is 1,3-benzothiazole, are reported together with those of its dicationic AsF6(-) salt, [Cu(hfac)2(TTF-CH═CH-BTA)2](AsF6)2, in which each TTF part is in a radical cation state. In these Cu(II)(hfac)2 complexes, two ligands are bonded to the central Cu atom of the Cu(hfac)2 part through the nitrogen atom of the 1,3-benzothiazole ring and occupy the two apical positions of the Cu(hfac)2 complex with an elongated octahedral geometry. These two ligands are located parallelly in a transverse head-to-tail manner, and the Cu(hfac)2 moiety is closely sandwiched by these two ligands. In the AsF6(-) salt of the Cu(hfac)2 complex, each TTF dimer is separated by the AsF6(-) anions and has no overlap with each other within the one-dimensional arrays, resulting in an insulating behavior. Both Cu(hfac)2 complexes showed the simple Curie-like temperature dependence of paramagnetic susceptibilities (χM), indicating that no interaction exists between the paramagnetic Cu(II) d spins. Furthermore, crystal structure analysis and magnetic/conducting properties of a radical cation ReO4(-) salt of the Cu(I) complex with two TTF-CH═CH-BTA ligands, [Cu(TTF-CH═CH-BTA)2](ReO4)2, are also described. Two nitrogen atoms of the ligands are connected to the central Cu(I) in a linear dicoordination with a Cu-N bond length of 1.879(9) Å. Two TTF parts of the neighboring complexes form a dimerized structure, and such a TTF dimer forms a one-dimensional uniform array along the a direction with a short S-S contact of 3.88 Å. Magnetic property measurement suggested the existence of a strongly antiferromagnetic one-dimensional uniform chain of S = 1/2 spins that originate from the radical cation states of the TTF dimers. Due to the construction of the one-dimensional uniform array of the radical cation state of the TTF dimer along the a axis, a semiconducting behavior is observed with σ(rt) = of 6 × 10(-5) S cm(-1) and an activation energy of E(a) = 0.16 eV.

Spin state transition in the ferromagnet Sr 0.9Ce 0.1CoO 2.85

The sample Sr 0.9Ce 0.1CoO 2.85, prepared by a chemical method, has a cubic perovskite structure with lattice parameter, a = 3.8368 ( 2 ) Å . The effective magnetic moment obtained from temperature dependent paramagnetic susceptibility suggests that the cobalt ions, Co 3+ (50%) and Co 4+ (50%), are in the intermediate spin states (IS), Co 3+ (t 2g 5e g 1) and Co 4+ (t 2g 4e g 1). Further, this compound undergoes a ferromagnetic as well as a metal–metal transition at T C ∼ 160 K which coincides with a spin state transition of cobalt ions that is likely to be associated with the IS state of Co 3+ (t 2g 5e g 1) ions going to the low spin (LS) state (t 2g 6e g 0) as inferred from the softening of infrared optical phonons.

Analysis of the magnetic properties of (La1 − x Sr x )0.93MnO3 manganites at high temperatures

For the first time, the Faraday method is used to measure the temperature dependence of paramagnetic susceptibility χ(T) of (La1 − x Sr x )0.93MnO3 (x = 0.2, 0.25, or 0.3) manganites in the temperature interval 60–850°C. It is demonstrated that the dependences have two kinks and three linear sections. The kink of curve χ−1(T) is related to polymorphic transformations (Q′ → Q* and Q* → R) that take place in the crystal lattices of the samples. The main magnetic characteristics of the samples are determined with the least-squares processing of curve χ−1. Is is demonstrated that dependence χ−1(T) obeys the Curie-Weiss law. The energy state of the magnetoactive manganese atom in the Q′-and Q*-phase samples is close to the energy state of a free Mn2+ ion. In the R phase, this state is close to the state of a free Mn3+ ion.

Mixed alkali effect in Li2O–Na2O–B2O3 glasses containing CuO – An EPR and optical study

Electron Paramagnetic Resonance (EPR) and optical absorption spectra of 0.5mol% CuO doped xLi2O–(30−x)Na2O–69.5B2O3 (5⩽x⩽25) mixed alkali glasses have been investigated. The EPR spectra of all the investigated samples exhibit resonance signals characteristic of Cu2+ ions in octahedral sites with tetragonal distortion. It is found that the spin-Hamiltonian parameters do not vary much with x. It is interesting to observe that the number of Cu2+ ions participating in resonance (N) and its paramagnetic susceptibility (χ) exhibits the mixed alkali effect with composition. It is observed that the temperature dependence of paramagnetic susceptibility (χ) obeys Curie–Weiss law. The paramagnetic Curie temperature (θp) is negative for the investigated sample, which suggests that the copper ions are antiferromagnetically coupled by negative super exchange interactions at very low temperatures. A broad band corresponding to the transition 2B1g→2B2g in the optical absorption spectrum shows a blue shift with x. By correlating the EPR and optical absorption data, the molecular orbital coefficients α2 and β12 have been evaluated. It is interesting to observe that the optical band gap (Eopt) and Urbach energies (ΔE) exhibit the mixed alkali effect. The theoretical values of optical basicity (Λth) have also been evaluated.

Comment on “Spectra and energy levels of Er3+(4f11) in NaBi(WO4)2” [J. Appl. Phys. 94, 7128 (2003)

A recent article by Gruber et al. [Gruber, J. Appl. Phys. 94, 7128 (2003)] reports the measurements of the optical absorption and photoluminescence spectra of Er3+ in NaBi(WO4)2 (NBW) and the results of the interpretation and fitting of the observed crystal-field (CF) splitting of Er3+ multiplets with a quasicenter model. In the light of available, previously published information, we argued that these conclusions are not warranted. As a proof, the composition of the Er3+-NBW wave functions and the energy levels derived from the final obtained CF parameters have been checked through the simulation of the temperature-dependent paramagnetic susceptibility χm according to the Van Vleck formalism and, unfortunately, experimental curves of χm versus T, measured in parallel and perpendicular directions to the c axis of the NBW crystal, were not adequately reproduced. The same simulation was carried out with a set of free ions and CF parameters resulting from our previous polarized CF analysis of Er3+ in a NBW crystal, and the agreement with the measured χm versus T curves is a clear indication of the validity and physical meaning of our earlier performed CF analysis.

The study of thermodynamic properties of PrNi 5

We have studied the influence of interaction of magnetic ions with conduction electrons on the thermodynamic properties of PrNi5 rare earth intermetallic compound. Starting in the zero approximation from the model of the crystal field and using equations of the thermodynamic perturbation theory, we have derived the formalism for evaluation of the partition function in the n-th order. The computations of higher order terms were performed by symbolic programming. The derived formalism was applied for explanation of temperature dependence of paramagnetic susceptibility, specific heat and electrical resistivity of PrNi5 compound.

Spin susceptibility of the superfluid3He−Bin aerogel

The temperature dependence of paramagnetic susceptibility of the superfluid ^{3}He-B in aerogel is found. Calculations have been performed for an arbitrary phase shift of s-wave scattering in the framework of BCS weak coupling theory and the simplest model of aerogel as an aggregate of homogeneously distributed ordinary impurities. Both limiting cases of the Born and unitary scattering can be easily obtained from the general result. The existence of gapless superfluidity starting at the critical impurity concentration depending on the value of the scattering phase has been demonstrated. While larger than in the bulk liquid the calculated susceptibility of the B-phase in aerogel proves to be conspicuously smaller than that determined experimentally in the high pressure region.

A uniform and one-dimensional stacking of 2,5-dichlorotetracyanoquinodimethanide molecules in the tetramethylarsonium salt.

In the tetramethylarsonium salt of 2,5-dichloro-7,7,8,8-tetracyanoquinodimethanide [systematic name: tetramethylarsonium 2,2'-(2,5-dichlorocyclohexa-2,5-diene-1,4-diylidene)bis(propanedinitrile)], C(4)H(12)As(+).C(12)H(2)Cl(2)N(4)(-) or [As(CH(3))(4)](C(12)H(2)Cl(2)N(4)), the cation lies disordered about a twofold axis and the radical ion lies about an inversion center forming a uniform [interplanar distance 3.35 (2) A] and one-dimensional stacking without any slip. The electrical conductivity of the single crystal at room temperature was less than 10(-9) S cm(-1), and the temperature dependence of paramagnetic susceptibility obeyed a one-dimensional antiferromagnetic Heisenberg model with a spin-exchange integral of 83 K in the temperature range 1.8-320.0 K.

Crystal structures and electrical conducting/magnetic properties in 1 ∶ 1 FeCl4 and FeBr4 salts of dimethylthio- and ethylenedithio-(1,3-dithiolylidene)thioxotetrathiafulvalene radical cations

The 1 ∶ 1 radical cation salts of new donor molecules, dimethylthio- (1) and ethylenedithio-(1,3-dithiolylidene)thioxotetrathiafulvalenes (2) with a magnetic FeCl4 or FeBr4 counteranion (1·FeBr4, 2·FeCl4 and 2·FeBr4) were prepared, and their electrical conducting and magnetic properties were investigated. The room-temperature electrical conductivities of 1·FeBr4 (compressed pellet), 2·FeCl4 (single crystal) and 2·FeBr4 (single crystal) were <10−5, 1.8 × 10−4 and 7.0 × 10−2 S cm−1, respectively. The temperature dependence of paramagnetic susceptibility obeyed the Curie–Weiss law in all cases, and the Curie constant (C) and Weiss temperature (θ) were as follows: C = 4.61 emu K mol−1 and θ = −5.4 K for 1·FeBr4; C = 4.53 emu K mol−1 and θ = −13.4 K for 2·FeCl4; C = 4.55 emu K mol−1 and θ = −31.2 K for 2·FeBr4. The remarkably different θ values between the three salts, considered together with their crystal structures, suggest significant interaction between Fe(III) spins by aid of π spins on 1 or 2 molecules.

Synthesis and magnetic properties of (C5H5)3Ce·HMPA

The 1:1 adduct (C5H5)3Ce·OP(NMe2)3 of cerium(III)-triscyclopentadienide with hexamethylphosphoric triamide (HMPA) was synthesized, isolated, purified and characterized by elemental analysis, IR- and 1H-NMR spectroscopy. The 1H-NMR spectrum obtained in solution in CDCl3 at room temperature exhibits a single signal for the Cp-proton at 5.6 ppm and a signal for the CH3-proton of the base HMPA at 0.49 ppm. The paramagnetic shift due to the Ce(III) ion could be evaluated by comparison to the corresponding signals of the homologous diamagnetic compound Cp3La·HMPA. The temperature-dependent paramagnetic susceptibility of the compound was measured within the temperature range from 4.2 up to 300 K. From the 1/χmol vs. T-plot the empirical constant C=0.78 m3 K mol−1 was evaluated with a Curie-Weiss constant θ of −71 K. The temperature dependence of the magnetic moment (μeff) is consistent with a Ce(III) ion. The ground state of the Ce ion is only partially populated. The magnetic moment at room temperature is 2.25 μB, an indication of covalency, as it has been observed for several Ce(III)-organometallics.

Electron density of states and spin fluctuations in weak itinerant magnets

The influence of zero-point and thermal spin fluctuations on the electronic structure and magnetic properties of weak itinerant magnets is considered. The possibility of considerable complex reconstruction of electron state density in fluctuating exchange and charge fields is demonstrated for Fe1−xCoxSi. The temperature dependence of paramagnetic susceptibility is in agreement with experimental data obtained for Fe1−xCoxSi.

Itinerant-electron theory of metamagnetism

Itinerant-electron theory of metamagnetism taking into account the effect of spin fluctuations is proposed on the Hubbard model within the static approximation in the functional integral formalism. It is possible to treat the metamagnetism of the system with large amplitudes of the moment and spin fluctuation. Effects of spin fluctuations and Stoner excitations on the temperature-dependence of paramagnetic susceptibility and the metamagnetic transition under external magnetic field are investigated numerically on a simple model (electronic) density of states. It is shown that both effects are quantitatively important in metamagnetism.

Paramagnetic susceptibility simulations from crystal field effects on rare earth antimonates R3Sb5O12

The magnetic susceptibilities of polycrystalline rare earth antimonates R3Sb5O12 (R=rare earth), with cubic structure, space group I43m (No. 217), where the point site symmetry of R is S4, have been measured from 4.2 to 800K. Using the wave functions and energy levels derived from standard free ion and crystal field parameters deduced from the analysis of the optical spectra of pure and/or doped Pr, Nd, Eu and Er compounds, the calculation of the temperature dependent paramagnetic susceptibility has been carried out according to the Van Vleck formalism. The same calculation through crystal field parameters resulting from the ab initio simple overlap model over the entire R3Sb5O12 series has been performed. Curves of both kinds were very similar for each configuration, with the exception of those for the Pr compound. Very good agreements with experimental data are found, especially below around 400K, even when the approximate D2d (near S4) potential is considered. The standard crystal field treatment of 4fN configurations is shown to explain the magnetic properties of these compounds with no need to consider any sort of magnetic interaction between the magnetic ions.

Magnetic Susceptibility of Liquid Ge–Se Alloys

The dependence of magnetic susceptibility on composition for liquid Ge 1- c Se c alloys exhibits a broad minimum around the composition c = 0.72 in the temperature range of 1023–1223 K. At higher temperatures, the broad minimum moves to the composition c = 0.5. The exponential temperature dependence of paramagnetic susceptibility on the Se-rich side can be explained by the formation of the Curie-like spin states. The movement of broad minimum is caused by a rapid increase in the Curie-like spin states with increasing temperature. The paramagnetic susceptibility on the Ge-rich side depends mainly on the density of states at the Fermi level.

Paramagnetic susceptibility simulations from crystal-field effects on rare-earth double molybdate and tungstate

Magnetic susceptibilities of polycrystalline samples of two series of double rare-earth molybdate and tungstate compounds, (RE = rare earth, X = Mo or W), with scheelite-type structure, space group (No 88), where RE atoms adopt point symmetry, have been measured in the temperature range 1.7 - 400 K. Using the wavefunctions and energy levels derived from standard free-ion and crystal-field parameters deduced from the analysis of the optical spectra of some selected (Pr, Nd and Eu) compounds, a systematic calculation of the temperature-dependent paramagnetic susceptibility, for all rare-earth configurations on the two series, has been carried out according to the Van Vleck formula. Very good agreements with experimental data are found over the whole temperature range. The standard crystal-field treatment of ions is shown to explain the magnetic properties of these compounds, for which no kind of magnetic interaction among the rare-earth ions has been detected.

Oxo-bridged bimetallic organouranium complexes: The crystal structure of μ-oxo-bis[tris(cyclopentadienyl)uranium(IV)

Oxidation of (C 5H 5) 3U III·THF with oxygen in tetrahydrofuran yields the linear bridged complex [(C 5H 5) 3U][μ-O]. Three cyclopentadienyl rings are η 5-covalently bonded to each uranium atom to form a distorted tetrahedron with one bridging oxygen atom. The UOU angle is 180° with the oxygen atom on a centre of inversion. The UO distance, 2.0881(4) Å, is among the shortest ever observed. The temperature-dependent paramagnetic susceptibility of the compound was measured in the temperature range between 4.2 and 300 K and is discussed in comparison with the magnetic susceptibilities of (C 5H 5) 3UOH, (C 5H 5) 3USH and [(C 5H 5) 3U] 2[μ-S].

Magnetic Properties of Phenyl Nitronyl Nitroxides

Abstract Magnetic properties and crystal structures of several derivatives of phenyl nitronyl nitroxide (abbreviated as PNN; 2-phenyl-4,4,5,5-tetramethyl-4,5-dihydro-lH-imidazol-l-oxyl-3-N-oxide) are investigated. Some of them have the intermolecular interactions between the nitroxide group and the phenyl group, which are suggested to be favorable to ferromagnetic coupling. As a result of the coexistence of different types of magnetic interactions, anomalies in the temperature dependence of paramagnetic susceptibility are found for some compounds.

Spin-correlated crystal-field analysis and temperature-dependent paramagnetic susceptibility of neodymium gallium garnet

The crystal-field energy levels and temperature-dependent paramagnetic susceptibility of neodymium gallium garnet (NdGG), Nd 3Ga 5O 12, are analyzed in terms of a model Hamiltonian defined to include spin-correlated crystal-field (SCCF) effects. A parametrized form of this Hamiltonian is used to fit the energies reported for 104 crystal-field levels split out of 30 different multiplets of the Nd 3+ (4 f 3) electronic configuration. Comparisons of energy level fits carried out with and without the inclusion of SCCF terms in the model Hamiltonian suggest the possible importance of SCCF effects in NdGG. Temperature-dependent paramagnetic susceptibility data are also reported for NdGG, and these data are reasonably well accounted for by calculations based on the eigenvalues and eigenvectors obtained from the crystal-field analyses.

Crystal field effect and temperature dependence of paramagnetic susceptibility

Based on the general Van Vleck evpression for the paramagnetic susceptibility, a critical review of particular, approvimate formulae used in practice for the temperature dependence of the susceptibility of bound ions in crystal fields of different symmetries is presented. The formulae correspond to the limit forms of the general Van Vleck evpression when Δ/ kT is very small, small or large, and Δ is the crystal field energy gap between the levels. The derived formulae have meaningful physical sense and the intervening constants are determined by the low- and high-frevuency Van Vleck terms of the susceptibility, energy parameters and so-called magnetic centre of gravity of the level system. It has been shown that the commonly used Curie-Weiss law, as a generalivation of the Curie law, has in most cases no physical justification and vuantities such as effective moment and Weiss constant possess only pure formal meaning. The conditions on its correct application are discussed. In the case of temperature independent paramagnetism ( Δ/ kT > 3) some practical correlations between its value and the range of its temperature independency are given. In many cases these correlations allow one to identify the ground state of the paramagnetic ion. The phenomenon of a mavimum in the paramagnetic susceptibility resulting from the competition between the temperature decay ( 1 T ) of the low-frevuency contribution of the evcited level and the evponential increase of its thermal population is considered. In the case when evchange interactions have to be taken into account the corresponding transformations of the temperature dependences of the paramagnetic susceptibility and renormalivation of the constants are given. As an evample the approach presented is applied to interpretation of χ( T) dependence and the correlations with the crystal field splitting for several actinide compounds.