Temperature-independent Term Research Articles

Muon Knight shift in palladium

The Knight shift at positive muons implanted in pure palladium has been measured as a function of temperature from 19.8 to 883 K. The Knight shift variation is strictly proportional to the Pd magnetic susceptibility with Δ K μ/Δ x =-(0.43±0.02) mole/emu=-(2.39±0.11)kG/μ B . A temperature independent term K μ( x=0)=+45±10 ppm is found. The results are discussed in terms of the electronic structure of H in Pd.

Bottleneck Effect on the ESR Linewidth in Pb1-xMnxTe Crystals

ESR measurements at V-band region have been made on Pb 1- x Mn x Te (\(0.6 \leqq x \lesssim 3\) at.%) in the temperature range, 2∼300 K. The temperature dependence of the linewidth Δ H consists of a temperature-dependent term and a temperature-independent residual term. The variation of the temperature coefficient of the linewidth with Mn density strongly supports the predominance of the bottleneck effect arising from the s-d exchange interaction between the Mn spins and the carrier spins. Exchange narrowing as well as dipolar broadening have been found to be effective, depending on the Mn density.

Muon Knight shift in palladium

Abstract The Knight shift at positive muons implanted in pure palladium has been measured as a function of temperature from 19.8 to 883 K. The Knight shift variation is strictly proportional to the Pd magnetic susceptibility with Δ K μ /Δ x =-(0.43±0.02) mole/emu=-(2.39±0.11)kG/μ B . A temperature independent term K μ ( x =0)=+45±10 ppm is found. The results are discussed in terms of the electronic structure of H in Pd.

Physical properties of first and second stage lithium graphite intercalation compounds

The second stage lamellar compound of graphite with lithium (LiC 12) has been investigated by specific heat and magnetic susceptibility experiments at low temperatures. The heat capacity thermal variation in the He 4 temperature range is fitted, as usual, with linear and cubic T-dependent terms. This fit allows us to calculate the density of levels at Fermi energy: N( E F) = 2.2 ± 0.2 eV −1 molecule −1 and the Debye temperature θ D = 142 K for a mole of product. The magnetic measurements between 295 and 5 K, indicate a temperature independent term χ exp = (0.85 ± 0.10)10 −6 emu CGS g −1 . After corrections for the usual core diamagnetism we obtain a mean Pauli component equal to (1.85 ± 0.2)10 −4 emu CGS mole −1 which is about twice as large as expected from the above calculated N( E F). Comparison of these experimental data with those already obtained for the first stage compound has been made. Referring to other physical properties, such as e.p.r., and plasma resonance, it is shown that these materials behave as weakly anisotropic 3D electronic systems.

Ferromagnetism in TiMn ternary hydrides

The magnetic behaviour of TiMn intermetallics and their hydrides was investigated by susceptibility measurements in the temperature range 5–360 K and magnetization measurements in the temperature range 4–250 K with fields up to 7.2 T. The three TiMn intermetallics that are stable at low temperature (the C14 Laves phase with a wide range of homogeneity from Ti 0.33Mn 0.67 to Ti 0.45Mn 0.55, the ρ phase Ti 0.46Mn 0.54 and the φ phase Ti 0.48Mn 0.52) are paramagnetic with susceptibilities that are independent of temperature. The Laves-phase hydride retains the C14 structure with a lattice volume expansion of 27%. All three hydrides are ferromagnetic with Curie temperatures T c of about 212, 87 and 155 K respectively that are slightly dependent on the hydrogen content. The susceptibilities above T c consist of Curie-Weiss terms and very large temperature-independent terms. The onset of ferromagnetism in these TiMn ternary hydrides is due to the volume expansion and/or to the increase in the density of states at the Fermi level on hydrogenation.

Solitons in Polyacetylene: Magnetic Susceptibility

The absoulte spin susceptibility of As${\mathrm{F}}_{5}$-doped trans-polyacetylene, ${[\mathrm{CH}{(\mathrm{As}{\mathrm{F}}_{5})}_{y}]}_{x}$, was determined by spin resonance techniques for $0.0004<~y<~0.138$. The Curie-law contribution decreases above $y=0.001$ to a level less than 1 ppm in the highly conducting regime. The temperature-independent Pauli term is small (\ensuremath{\le}5\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}8}$ emu/mole) for $y<0.01$, remains small up to $y=0.05$, and shows an abrupt increase near $y=0.07$ to a value of \ensuremath{\sim} 3 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}6}$ emu/mole at higher concentrations. The results are consistent with the soliton doping mechanism.

Magnetic susceptibilities and knight shifts of the intermetallic compounds NdCu 4 and NdCu 5

The magnetic susceptibility and Knight shift of the intermetallic compounds NdCu 4 and NdCu 5 were investigated over the temperature range 80–850 K. The most important contributions to the magnetic susceptibility are the Curie-Weiss term, expressing the paramagnetism of the localized 4ƒ-electrons, and a temperature independent term, both of which have been determined. The phenomenological quantity J sƒ between the 4ƒ-electron and conduction electron spins was found to be −2.46.10 −3eV for NdCu 4 and 1.35.10 −3 eV for NdCu 5. A reversal in the sign of the s-ƒ coupling for CeCu 5 was noted.

Inorganic photophysics in solution. Part 4.—Deactivation mechanisms of the 2Eg state of CrIII complexes from lifetime studies

The temperature dependences of the luminescence lifetimes, τlum, of several CrIII complexes of particular photochemical interest have been determined over temperature ranges 77–370 K in a variety of media, especially 9 mol dm–3 LiCl + H2O and cellulose acetate film. In most cases, klum fits an expression kTl+ANR exp(–ΔE[graphic omitted]NR/RT) where the subscripts refer to temperature-independent and (temperature-dependent) non-radiative terms. The strong solvent-dependence of ΔE[graphic omitted]NR, which is always only a fraction of the 4T2g–2Eg splitting, suggests a chemical pathway for deactivation of the 2Eg state rather than a purely physical route such as back-intersystem crossing. For complexes which have been examined in a wide variety of media, values of ln ANR correlate fairly well with those of ΔE[graphic omitted]NR, implying a common overall mechanism.

Inorganic photophysics in solution. Part 6.—Isotope effects in the non-radiative deactivation of photo-excited uranyl [UO2]2+ ion in hydroxylic solvents

The effect of deuterium substitution on τ(UO2+2)* has been measured in H2O, mildly acidic H2O, strong aqueous LiCl and liquid methanol, in most cases over an extended temperature range (77 K to the boiling point). In all media, a strongly temperature-activated term dominates non-radiative processes at room temperature, whilst a temperature-independent term is effective both at 77 K and, in all cases, at considerably higher temperatures. Both effects are sensitive to substitution of the solvent by deuterium atoms: in the case of methanol that of C—H (but not of O—H) is important at room temperature, but that of O—H is especially significant at 77 K. The low-temperature deactivation mechanism is concluded to be due neither to fast, reversible abstraction of a hydroxylic H atom (because of the zero activation energy), nor to fast, reversible electron transfer (because of the isotope effect), but to a physical process.

Experimental magnetic-susceptibility study of the electronic properties of liquid Se-Te alloys

The electronic properties of liquid Se-Te alloys have been investigated by measurement of the magnetic susceptibility $\ensuremath{\chi}$ in a temperature range up to 1100\ifmmode^\circ\else\textdegree\fi{}C. $\ensuremath{\chi}$ is assumed to be composed of a temperature-independent diamagnetic term ${\ensuremath{\chi}}_{D}$ and a paramagnetic contribution ${\ensuremath{\chi}}_{p}$. ${\ensuremath{\chi}}_{D}$ is found to be a linear function of composition. In the Te-rich alloys, ${\ensuremath{\chi}}_{p}$ is proportional to the square root of electrical conductivity indicating diffusive electronic transport. In the Se-rich alloys, the temperature dependence of ${\ensuremath{\chi}}_{p}$ is found to be exponential with a composition-independent activation energy of 0.68 eV. This is interpreted as the energy required to produce a paramagnetic dangling bond. The entropy of bond breaking is found to increase strongly with Te content.

Thermodynamics of the partially miscible system ethanol + hexadecane

The following properties of ethanol + hexadecane are reported: vapour pressure at 325.25 K; enthalpy of mixing at 298.15, 308.15, 318.15, and 325.25 K; compositions of coexisting phases from 298.15 to 325.25 K; excess volumes at 298.15 and 318.15 K. From these results activity coefficients and partial enthalpies of both components are calculated. The experimental results are interpreted by a model of association of ethanol molecules into open-chain and cyclic hydrogen-bonded groups with allowance for a non-polar interaction. The activities and enthalpies are well reproduced, and phase separation is predicted, but the compositions of the conjugate phases cannot be quantitatively accounted for with the single temperature-independent non-polar interaction term which suffices for the other properties.

Influence of frequency and temperature on the conduction-electron spin-resonance linewidth andgvalue in copper

The CESR linewidth and $g$ value of pure Cu is measured over the temperature range 4.2 to 50 K at the frequencies of 9.27, 21, and 59.6 GHz. The linewidth is shown to have a linearly frequency dependent, but temperature-independent term giving 0.040\ifmmode\pm\else\textpm\fi{}0.002 mT/GHz. A second term, when ascribed to partial breakdown of motional narrowing, is found to be much weaker than proposed elsewhere. The $g$ value is found also to be temperature and frequency dependent.

Static and dynamic properties of localized Mn moments in liquid bismuth

We present measurements of static susceptibility and of $^{55}\mathrm{Mn}$ and $^{209}\mathrm{Bi}$ NMR shifts and relaxation times over temperatures ranging from 700 - 1400 K for a series of dilute alloys of Mn in liquid Bi. The Mn impurities, which possess a local moment similar to that of $\mathrm{Cu}\mathrm{Mn}$, are found to exhibit a Kondo temperature ${T}_{K}\ensuremath{\sim}50$ K. A plot of $^{55}\mathrm{Mn}$ shift versus measured impurity susceptibility reveals a small temperature-independent susceptibility term in addition to the Curie-Weiss term. The fluctuation rate of the Mn moment is deduced from relaxation measurements of the $^{55}\mathrm{Mn}$ nuclei, yielding a single-ion term in good agreement with the dynamic susceptibility model for Kondo systems given by G\"otze and Schlottmann, and a spin-spin Ruderman-Kittel-Kasuya-Yosida (RKKY) term in reasonable accord with realistic model calculations for nearfield RKKY exchange. Failure of the $^{209}\mathrm{Bi}$ shift to follow the Mn susceptibility is attributed to temperature-dependent transferred hyperfine coupling; a successful interpretation of this effect is made using x-ray and neutron-diffraction results to determine the temperature-dependent radial distribution function and employing a simple asymptotic model of the RKKY spin-density oscillations. The RKKY amplitude so determined is found to be anomalously large, while the phase (at near-neighbor distances) is in agreement with a recent model calculation for $\mathrm{Cu}\mathrm{Mn}$. By applying a small correction to the moment fluctuation times from liquid motion, we are also able to obtain a quantitative interpretation of the $^{209}\mathrm{Bi}$ relaxation times.

AB INITIO calculations of the electronic properties of [formula omitted

The magnetic susceptibility and Knight shift of the intermetallic compounds NdCu4 and NdCu5 were investigated over the temperature range 80–850 K. The most important contributions to the magnetic susceptibility are the Curie-Weiss term, expressing the paramagnetism of the localized 4ƒ-electrons, and a temperature independent term, both of which have been determined. The phenomenological quantity Jsƒ between the 4ƒ-electron and conduction electron spins was found to be −2.46.10−3eV for NdCu4 and 1.35.10−3 eV for NdCu5. A reversal in the sign of the s-ƒ coupling for CeCu5 was noted.

Knight shifts and magnetic susceptibilities of the intermetallic compounds CeCu 4 and CeCu 5

The magnetic susceptibility and Knight shift of the compounds CeCu 4 and CeCu 5 have been measured over the temperature ranges 80–800 and 140–400 K, respectively. The most important contributions to the magnetic susceptibility are the Curie-Weiss term, expressing the paramagnetism of the localized ƒ-electrons, and a temperature independent term, which have both been determined. The phenomenological exchange integral F sƒ between the 4ƒ-electron spins and conduction electron spins was found to be −10.43× 10 −3 eV for CeCu 4 and 3.9 × 10 −3 eV for CeCu 5. A reversal in the sign of the s−ƒ coupling for CeCu 5 is noted.

NMR and magnetic susceptibility of Gd 2Cu 6Al 11 and Gd 2Co 6Al 11 intermetallic compounds

27Al Knight shifts and the magnetic susceptibilities of Gd 2Cu 6Al 11 and Gd 2Co 6Al 11 are reported. The contributions to the magnetic susceptibility are Curie-Weiss terms expressing the paramagnetism of the localized f and d electrons of Gd and Co atoms, and a temperature-independent term. The phenomenological exchange constant γ sf between 4 f-electron spins and conduction electron spins in both the compounds is derived to be −1.26 × 10 −3 eV. In the Gd 2Co 6Al 11 system the Co moment couples with the 27Al nucleus through two mechanisms: (1) through direct overlap between the Co 3 d orbitals and the Al core electrons, leading to core polarization, and (2) through conduction electron polarization. The corresponding phenomenological exchange constants γ i sd and γ e sd are derived to be −0.0375 and 1.33 × 10 −3 eV, respectively.

Electron spin-lattice relaxation mechanisms of radiation produced trapped electrons and hydrogen atoms in aqueous and organic glassy matrices: modulation of electron nuclear dipolar interaction by tunnelling modes in a glassy matrix

The spin lattice relaxation of trapped electrons in aqueous and organic glasses and trapped hydrogen atoms in phosphoric acid glass has been directly studied as a function of temperature by the saturation recovery method. Below 50 to 100 K, the major spin lattice relaxation mechanism involves modulation of the electron nuclear dipolar(END) interaction with nuclei in the radical's environment by tunnelling of those nuclei between two or more positions. This relaxation mechanism occurs with high efficiency and has a characteristic linear temperature dependence. The tunnelling nuclei around trapped electrons do not seem to involve the nearest neighbour nuclei which are oriented by the electron in the process of solvation. Instead the tunnelling nuclei typically appear to be next nearest neighbours to the trapped electron. The identities of the tunnelling nuclei have been deduced by isotopic substitution and are attributed to: Na in 10 mol dm–3 NaOH aqueous glass, ethyl protons in ethanol glass, methyl protons in methanol glass and methyl protons in MTHF glass. For trapped hydrogen atoms in phosphoric acid, the phosphorus nuclei appear to be the effective tunnelling nuclei. Below ∼10 K the spin lattice relaxation is dominated by a temperature independent cross relaxation term for H atoms in phosphoric acid glass and for electrons in 10 mol dm–3 NaOH aqueous glass, but not for electrons in organic glasses. This is compared with recent electron–electron double resonance studies of cross relaxation in these glasses. The spin lattice relaxation of O– formed in 10 mol dm–3 NaOH aqueous glass was also studied and found to be mainly dominated by a Raman process with an effective Debye temperature of about 100 K.

Magnetic susceptibility of the uranium nitrides

The magnetic susceptibility of UN, and of the higher uranium nitrides has been measured over a wide temperature range, i.e., 4.2–950 K. A large temperature-independent term χ 0 equal to 310 ± 10 × 10 −6 emu/mole has been derived from the total susceptibility data of UN. The obtained χ M values of UN are also related to the Knight shift data from literature. For the higher nitrides U 2N 3+ x the magnetic susceptibility has been measured for N:U ratios between 1.55 and 1.80. Antiferromagnetic phase transitions have been found for all the examined compositions. The transition temperature T N gradually decreases as the nitrogen content increases, varying from 94 K for UN 1.55 to about 8 K for the maximum composition of UN 1.80±0.02. The magnetic properties of the higher nitrides are discussed in terms of mixed valency states, either U 4+ and U 6+ or U 4+ and U 5+ for the stoichiometric U 2N 3.

NMR and magnetic susceptibility of CeCu6

NMR and magnetic susceptibility of CeCu6 intermetallic compound were investigated. The most important contributions to the magnetic susceptibility are the Curie-Weiss term, expressing the paramagnetism of the localized f-electrons, and a temperature independent term for which all the contributions were estimated. The phenomenological exchange constantJsf between 4f — electron spins and conduction — electron spins is derived to be −0·012 eV. The Knight shift and Curie temperature are discussed in terms of the Ruderman-Kittel-Kasuya-Yosida theory and in the Rocher's virtual bound states model. The s — f exchange integralΓ and the Fermi wavevectorkF are derived to be — 0·8 eV and 1·32 A−1, respectively.

Susceptibility of Fe in Cu

The M\"ossbauer effect of Cu:Fe has been measured for $30 \mathrm{mK}<T<100 \mathrm{K}$ in external fields up to 60 kg. A constant temperature-independent term is subtracted from the hyperfine fields. After this correction the local susceptibility is in agreement with bulk magnetization, neutron diffraction, and NMR data. At the very lowest temperatures the local susceptibility becomes temperature independent, in agreement with theoretical expectations.