Isotope effect in charge transport of LuB12

The galvanomagnetic properties of single-crystal samples with various isotopic boron compositions have been investigated for the first time for the normal state of superconductor LuB₁₂ (T c ≈ 0.44 K). Precision measurements of the resistivity, Hall coefficient, and magnetic susceptibility have been performed over a wide temperature range of 2–300 K in magnetic fields up to 80 kOe. A change of the charge transport regime in this nonmagnetic compound with metallic conduction is shown to occur near T* ≈ 50−70 K. As a result, a sharp peak with significantly different amplitudes for Lu¹⁰B₁₂ and Lu¹¹B₁₂ is recorded in the temperature dependences of the Hall coefficient R _H(T) near T*. A significant (about 10%) difference (in absolute value) of the Hall coefficients R _H for the Lu¹⁰B₁₂ and Lu¹¹B₁₂ compounds at helium and intermediate temperatures has been found and the patterns of behavior of the dependence R _H(H) for T < T* in an external magnetic field H ≤ 80 kOe for Lu¹⁰B₁₂ and Lu¹¹B₁₂ are shown to differ significantly. Analysis of the Curie-Weiss contribution to the magnetic susceptibility χ(T) leads to the conclusion about the formation of magnetic moments μ_eff ≈ (0.13−0.19)μ_B in each unit cell of the fcc structure of LuB₁₂ compounds with various isotopic compositions. The possibility of the realization of an electronic topological 2.5-order transition near T* and the influence of correlation effects in the 5d-band on the formation of a spin polarization near the rare-earth ions in LuB₁₂ is discussed.     

On the behaviour of Er3+ ion in tetragonal crystalline field

Crystal field parameters for ErGaG and Er³⁺ YAlG and used to compute the temperature dependence of Schottky specific heat, paramagnetic susceptibility, magnetic anisotropy,μ _eff and quadrupole splitting in the range 10–400 K. The hyperfine interaction parametersA andB for¹⁶⁶Er and¹⁶⁷Er in both the systems are also obtained and in turn used to estimate the nuclear specific heat contribution. The studied parameters compare well with the available experimental results.     

Paramagnetic susceptibility of Bi-Mn alloys in the liquid state

The magnetic susceptibility of Bi_{100 − x} Mn _x (x = 5, 7.5, 10, 12.5, 15, 17.5, 20, 25) alloys is experimentally studied by the Faraday method in the temperature range T = 300−1200°C and the magnetic-field range B = 0.6−1.3 T. To calculate the electronic characteristics of the Bi-Mn alloys, the experimental results are approximated by the generalized Curie-Weiss law. The calculated parameters of the electronic structure of the alloys demonstrate that manganese is present in the melt in an ionic state with an effective magnetic moment μ_eff ≈ 5μ_B, all Bi-Mn alloys have negative paramagnetic temperatures (which indicate the antiferromagnetic character of the exchange between transition 3d element atoms), and the density of states near the Fermi level n(E _F) is low. Therefore, the Fermi level is outside the d band of manganese and its position is controlled by the sp band of bismuth.     

Magnetic Moment of the 3/2− Ground State of 185W

Nuclear magnetic resonance measurement have been performed for ¹⁸⁵W oriented at 8 mK in an Fe host. The magnetic hyperfine splitting frequency at an external magnetic field of 0.1 T was determined to be 196.6(2) MHz. With the known hyperfine field of B _hf = −71.4(18) T, the nuclear magnetic moment of ¹⁸⁵W is deduced as μ(¹⁸⁵W) = +0.543(14) μ_N.     

Effect of oxygen deficiency on the magnetic, electrical, magnetoelectric, and magnetoelastic properties of La1 ? x Sr x MnO3 ? δ manganites

This paper reports on a study of the effect of oxygen deficiency on the magnetic and electrical properties of the La_{1 − x} Sr _x MnO_{3 − δ} manganites (x = 0, 0.2, 0.4; δ = 0, 0.13, 0.2). In compositions with x = 0 and δ = 0.13 and 0.2, the temperature dependence of the magnetization M (T) can be approximated by the Langevin function with the moment of superparamagnetic clusters μ = 77μ_B (δ = 0.13) and 86μ_B (δ = 0.2) at temperatures of 25 K ≤ T ≤ 250 K, with the exception of a small temperature range near 132 K in which a maximum characteristic of the LaMnO₃ antiferromagnet is seen. These compositions, as well as Sr-doped compositions with δ ≠ 0, reveal a difference between the magnetizations of the sample cooled in a weak magnetic field and in zero field. At T = 6 K in a magnetic field of 16 kOe, the compositions with x = 0.2 and 0.4, δ = 0.13 possess a magnetic moment per formula unit lower than that with δ = 0, as well as reveal an anomalous relation between the Curie temperature T _C and the Curie paramagnetic point gJ, namely, T _C > gJ. The magnetization of compositions with x = 0.2 and 0.4, δ = 0.2 follows the Langevin function with μ = 40μ_B and 130μ_B, respectively. The electrical resistivity of samples with x = 0.4 and δ = 0.13 and 0.2 is one to two orders of magnitude larger than that of the composition with x = 0.4, δ = 0, which evidences partial or complete compensation of acceptor defects (Sr²⁺ ions) by donor defects (doubly charged O²⁻ vacancies). The above properties of oxygen-deficient compositions suggest that they contain an insulating ferro-antiferromagnetic magnetically double-phase state. The magnetoresistance and volume magnetostriction in samples with x = 0.4 and δ = 0, 0.13, and 0.2 are small; indeed, in a magnetic field of 8 kOe, they do not exceed 1.4% and 6 × 10⁻⁶, respectively. On this basis, it is concluded that the unbalanced doubly charged donors (O vacancies) are in the state with antiparallel spins and, thus, do not initiate the formation of ferron-type ferromagnetic clusters. The significance of both compensated and unbalanced doubly charged donors consists in that they give rise to the formation of fractured Mn-O-Mn bonds, which bring about lowering of the magnetic moment per formula unit in compositions with x = 0.2 and 0.4 and δ = 0.13 and the transition to superparamagnetism in compositions with x = 0.2 and 0.4, δ = 0.2. Original Russian Text ? L.I. Koroleva, D.M. Zashchirinskiĭ, T.M. Khapaeva, L.I. Gurskiĭ, N.A. Kalanda, V.M. Trukhan, R. Szymczak, B. Krzumanska, 2008, published in Fizika Tverdogo Tela, 2008, Vol. 50, No. 12, pp. 2201–2205.     

Electrical conductivity and magnetic properties of La1 ? xCaxMn1 ? yFeyO3 ceramic samples (x = 0.67, y = 0, 0.05)

The temperature dependences of the magnetic susceptibility χ(T) and the electrical resistivity ρ(T) of ceramic samples of La_{1 − x} Ca _x MnO₃ with x = 0.67 (LCMO) and La_{1 − x} Ca _x Mn_{1 − y} Fe _y O₃ with x = 0.67 and y = 0.05 (LCMFO) are investigated in magnetic fields B = 50–10⁵ G and the temperature range T = 4.2–400 K. Both samples undergo a transition from the paramagnetic state to a state with charge (orbital) ordering (CO) at temperatures T _CO ≈ 272 K for LCMO and T _CO ≈ 222 K for LCMFO. The behavior of the paramagnetic phase in the temperature range 320–400 K for LCMO and 260–400 K for LCMFO is described by the Curie-Weiss law with effective Bohr magneton numbers p _eff = 4.83 μ_B (LCMO) and 4.77 μ_B (LCMFO), respectively. The disagreement between the observed positive Weiss temperatures (θ ≈ 175 K (LCMO) and θ ≈ 134 K (LCMFO)) and negative Weiss temperatures required for the antiferromagnetic ground state can be explained by the phase separation and transition to the charge-ordered state. The magnetic irreversibility for T < T _CO is accounted for by the existence of a mixture of the ferromagnetic and antiferromagnetic phases, as well as the cluster glass phase. At low temperatures, doping with iron enhances the frustration of the system, which manifests itself in a more regular behavior of the decay rate of the remanent magnetization with time. The temperature dependence of the electrical resistivity in the range of the charge-ordered phase conforms to the variable-range hopping model. The behavior of the electrical resistivity is governed by the complex structure of the density of localized states near the Fermi level, which includes a soft Coulomb gap Δ = 0.464 eV for LCMO and 0.446 eV for LCMFO. It is established that the ratio between the localization radii of charge carriers a for LCMFO and a _und for LCMO is a/a _und = 0.88. Original Russian Text ? V.S. Zakhvalinskiĭ, R. Laiho, T.S. Orlova, A.V. Khokhulin, 2008, published in Fizika Tverdogo Tela, 2008, Vol. 50, No. 1, pp. 61–68.     

Manganese-doped ZnSiAs<Subscript>2</Subscript> chalcopyrite: A new advanced material for spintronics

A new spintronics material with the Curie temperature above room temperature, the ZnSiAs₂ chalcopyrite doped with 1 and 2 wt % Mn, is synthesized. The magnetization, electrical resistivity, magnetoresistance, and the Hall effect of these compositions are studied. The temperature dependence of the electrical resistivity follows a semiconducting pattern with an activation energy of 0.12–0.38 eV (in the temperature range 124 K ≤ T ≤ 263 K for both compositions). The hole mobility and concentration are 1.33, 2.13 cm²/V s and 2.2 × 10¹⁶, 8 × 10¹⁶ cm⁻³ at T = 293 K for the 1 and 2 wt % Mn compositions, respectively. The magnetoresistance of both compositions, including the region of the Curie point, does not exceed 0.4%. The temperature dependence of the magnetization M(T) of both compositions exhibits a complicated character; indeed, for T ≤ 15 K, it is characteristic of superparamagnets, while for T > 15 K, spontaneous magnetization appears which correspond to a decreased magnetic moment per formula unit as compared to that which would be observed upon complete ferromagnetic ordering of Mn²⁺ spins or antiferromagnetic ordering of spins of the Mn²⁺ and Mn³⁺ ions. Thus, for T > 15 K, it is a frustrated ferro- or ferrimagnet. It is found that, unlike the conventional superparamagnets, the cluster moment μ _c in these compositions depends on the magnetic field: ∼12000–20000μ_B for H = 0.1 kOe, ∼52–55μ_B for H = 11 kOe, and ∼8.6–11.0μ_B at H = 50 kOe for the compositions with 1 and 2 wt % Mn, respectively. The specific features of the magnetic properties are explained by the competition between the carrier-mediated exchange and superexchange interactions.     

Influence of elastic strain onμ + SR in α-iron single crystalsSR in α-iron single crystals

The spin-precession frequencies and the transverse spin relaxation rates of positive mouns (μ ⁺) have been measured on two elastically strained α-Fe single crystal platelets as well as on an unstrained reference α-Fe crystal at temperatures down to 2.7 K in applied magnetic field 0≤B _appl≤3 T. The drastic effects of the strains may be qualitatively understood in terms of their influence on both the magnetic domain structure and theμ ⁺ energies at the various interstitial sites. This leads to the conclusion that at low temperaturesμ ⁺ in α-Fe occupy configurations related to octahedral interstitials with dipolar fieldB _dip=0.70 T.     

Electronic structure of TiO<Subscript>2</Subscript> rutile with oxygen vacancies: Ab initio simulations and comparison with the experiment

The electronic structure of TiO₂ rutile with oxygen vacancies, which is a promising insulator, has been analyzed. The ab initio density functional calculations, as well as the comparative analysis of the results obtained in the σ-GGA spin-polarized generalized approximation and those obtained by the σ-GGA + U method with allowance for Coulomb correlations of d electrons titanium atoms in the Hartree-Fock approximation for the Hubbard model, have been performed. It has been found that the effective electron mass in rutile is anisotropic and there are both light (m _e ^* = (0.6–0.8)m ₀, where m ₀ is the free-electron mass) and heavy (m _e ^* > 1m ₀) electrons, whereas holes in rutile are only heavy (m _e ^* ⩾ 2m ₀). It has been shown that the σ-GGA + U method gives a deep occupied level in the band gap and that an oxygen vacancy in rutile is an electron and hole trap.     

Molecular Stark effect spectroscopy of diflavonol and inhomogeneous broadening of its electronic spectra in erythrocyte membranes

Using spectroscopy of the molecular Stark effect and fluorescence spectroscopy, we study the characteristics of diflavonol 3,7-dihydroxy-2,8-di(4-dimethylaminophenyl)-4H,6H-pyrano[3,2-g]chromene-4,6-dione (DFME), which demonstrates intramolecular charge and proton phototransfer. In the ground state, this dye has only one form and, in the excited state, it has two forms, i.e., normal and phototautomeric. We found that, for the normal form of DFME, the transition dipole moment that is responsible for the absorption (m _a ), the dipole moment in the equilibrium ground state (μ _g ), and the change of the dipole moment upon transition of the molecule in the excited Franck-Condon state (Δ ^a μ) are parallel. In the ground equilibrium state, the dipole moments in 1,4-dioxane and cyclohexane are equal to μg = 12.2 × 10⁻³⁰ C m and μ _g = 11.0 × 10⁻³⁰ C m, respectively. Upon excitation, they increase by Δ ^a μ = 61 × 10⁻³⁰ C m and Δ ^a μ = 50.2 × 10⁻³⁰ C m in these solvents. We study the spectral characteristics of DFME in organic solvents and erythrocyte membranes. A spectral inhomogeneity of DFME in erythrocyte ghosts is found. The inhomogeneous broadening of fluorescence spectra is manifested as a long-wavelength shift of the band of the normal form of DFME by 1640 cm⁻¹ upon excitation at the red edge of the absorption spectrum.     

Local Moment of Ir in Fe,Co and Ni Hosts Probed by Ir L 2,3 Edge X-Ray Magnetic Circular Dichroism

The formation of an induced 5d magnetic moment on Ir in Fe₉₇Ir₃, Co₉₅Ir₅ and Ni₉₅Ir₅ alloys has been investigated by X-ray magnetic circular dichroism (XMCD) and X-ray absorption spectra (XAS) measurements at Ir L _2,3 edges. Using a sum rule which relates the integrals of these spectra with the ground state expectation value of the orbital angular momentum 〈L _Z 〉 of the probed atom, the orbital moment m _orb of Ir could be determined as −0.071(2) μ _B in an Fe host, −0.067(2) μ _B in a Co host and −0.041(1) μ _B in a Ni host. The spin magnetic moment m _spin of Ir is also found to be the maximal in Fe and the minimal in Ni. The total moment of Ir is found to be approximately 1/5 of total moment of Fe, 2/13 of the total moment of Co, and 1/4 of the total moment of Ni. This revised version was published online in September 2006 with corrections to the Cover Date.     

Deformation change in light iridium nuclei from laser spectroscopy

Laser spectroscopy measurements have been performed on neutron-deficient and stable Ir isotopes using the COMPLIS experimental setup installed at ISOLDE-CERN. The radioactive Ir atoms were obtained from successive decays of a mass-separated Hg beam deposited onto a carbon substrate after deceleration to 1kV and subsequently laser desorbed. A three-color, two-step resonant scheme was used to selectively ionize the desorbed Ir atoms. The hyperfine structure (HFS) and isotope shift (IS) of the first transition of the ionization path 5d ⁷6s ²⁴ F _9/2 → 5d ⁷6s6p ⁶ F _11/2 at 351.5nm were measured for ^182-189Ir, ¹⁸⁶Ir ^m and the stable ^{191, 193}Ir. The nuclear magnetic moments μ_I and the spectroscopic quadrupole moments Q_s were obtained from the HFS spectra and the change of the mean square charge radii from the IS measurements. The sign of μ_I was experimentally determined for the first time for the masses 182≤A≤189 and the isomeric state ¹⁸⁶Ir ^m . The spectroscopic quadrupole moments of ¹⁸²Ir and ¹⁸³Ir were measured also for the first time. A large mean square charge radius change between ¹⁸⁷Ir and ¹⁸⁶Ir ^g and between ¹⁸⁶Ir ^m and ¹⁸⁶Ir ^g was observed corresponding to a sudden increase in deformation: from β₂ ≃ + 0.16 for the heavier group A = 193, 191, 189, 187 and 186m to β₂≥ + 0.2 for the lighter group A = 186g, 185, 184, 183 and 182. These results were analyzed in the framework of a microscopic treatment of an axial rotor plus one or two quasiparticle(s). This sudden deformation change is associated with a change in the proton state that describes the odd-nuclei ground state or that participates in the coupling with the neutron in the odd-odd nuclei. This state is identified with the π3/2⁺[402] orbital for the heavier group and with the π1/2^-[541] orbital stemming from the 1h _9/2 spherical subshell for the lighter group. That last state seems to affect strongly the observed values of the nuclear moments.     

Plasma parameters in the upgraded Trimyx-M Galathea

Results are presented from measurements of the plasma parameters in the upgraded Trimyx-M Galathea. After the barrier magnetic field and the energy of the injected hydrogen plasma bunch were increased to B _bar ∼ 0.1 T and W ₀ ≈ 200 J, respectively, the following plasma parameters were achieved: the density n ∼ 5 × 10¹³ cm⁻³, the plasma confinement time τ* = 800–900 μs, the elergy of the confined plasma W ₁ ∼ 100 J, the ratio of the plasma pressure to the barrier magnetic pressure β ₀ ∼ 0.2, the electron temperature T _e ∼ 20 eV, and the ion temperature T _i ∼ 2T _e . The maximum time during which the plasma density decreased e-fold, τ _p , was found to be 300 μs at B _bar = 0.1 T, which agrees with the classical transport model.     

Muons in type-II superconductors: μ+ diffusion in ultra-pure niobiumdiffusion in ultra-pure niobium

The diffusivityD _μ of positive muons (μ⁺) in the mixed state of superconducting high-purity, high-perfection niobium single crystals is investigated by measurements of the relaxation of the transverse muon spin polarization (μ⁺SR). The method makes use of the strong magnetic field gradients existing in the mixed state of Type-II superconductors and monitorsD _μ through the variation of the magnetic field felt by the μ⁺ during their diffusion through the crystals. For μ⁺ near the centres of the flux lines inNb it givesD _μ(4.6 K)=(8±2)·10⁻¹¹m²S⁻¹. The positive temperature coefficient ofD _μ indicates that at liquid-helium temperatures the diffusivity of μ⁺ inNb is mainly due to phonon-assisted tunnelling processes.     

Electronic structure and properties of strontium ferrite Sr3Fe2O6

The electronic structure of strontium ferrite Sr₃Fe₂O₆ was calculated using the tight-binding linear muffin-tin orbital method (TB LMTO) in the local spin density approximation of density functional theory with Coulomb correlations correction (LSDA+U). The semiconducting character of the spectrum with charge transfer energy gap of 1.82 eV was obtained in reasonably good agreement with experimental data. The iron ions are found to be in the high spin state. The calculated value of the local spin magnetic moment of Fe³⁺ ion is 3.94 μ_B which is not typical for trivalent iron ion in the high spin state. It is shown that the strong hybridization between Fe3d and O2p orbitals favors the d⁶ L configuration of Fe³⁺ ion, where L is a hole in the oxygen p shell. The mechanism of oxygen transport in ferrite is discussed basing on the total energy calculations of the different spatial configurations of oxygen vacancies.     

Mössbauer Studies of Dilute 119Sn and 57Fe in SrRuO3 and Sr2FeRuO6

Nuclear magnetic resonance on oriented ¹⁷⁵Hf in iron host has been measured. Samples of ¹⁷⁵HfFe were made by recoil implantation of the precursor ¹⁷⁵Ta isotope. The resonance frequency and the resonance line width have been determined to be 139.0 (1) MHz and FWHM = 2.7 (2) MHz, respectively, in an external magnetic field of 0.1 T. The resonance width was very narrow compared with the previously reported value of 11.0 (1.1) MHz. With the known value of the magnetic moment of μ(¹⁷⁵Hf) = −0.62 (3) μ_N, the hyperfine field has been deduced as B _HF = −73.6 (3.5) T.     

Neutrino radiation by an electon in quantizing nuclear and strong magnetic fields

The probability and intensity of neutrino radiation of a hydrogen-like atom in the strong magnetic field B >> Z ²α² B ₀, α = e ² = 1/137, B ₀ = m ²/e = 4.41⋅10¹³ G are determined. The temperature dependence of the intensity of an atom ensemble is analyzed.     

Possible observation of the coexistence of superconductivity and long-range magnetic order in NdRh4B4

The ternary rare earth compound NdRh₄B₄ has been studied by means of critical field, low temperature heat capacity, and static magnetic susceptibility measurements. Features in the upper critical field and heat capacity data at 1.31 K and 0.89 K suggest the occurrence of long-range magnetic order in the superconducting state. The temperature dependence of the static magnetic susceptibility follows a Curie-Weiss law with an effective magnetic moment μ_eff = 3.58 ± 0.05 μ_B and a Curie-Weiss temperature θ_p = ?6.2 ± 1.0 K between 20 K and room temperature. However,, magnetization vs. applied magnetic field isotherms suggest the development of a ferromagnetic component in the Nd³⁺ magnetization at low temperatures.     

Synthesis and magnetic properties of Cu3B2O6 single crystals

The temperature dependence of the magnetic susceptibility of Cu₃B₂O₆ single crystals grown by spontaneous crystallization from a melt consisting of a mixture of CuO and B₂O₃ and the behavior of their magnetization are investigated in magnetic fields up to 55 kOe. A broad susceptibility maximum is observed near 39 K, and a sharp drop in susceptibility is observed at T<10 K. The paramagnetic Néel temperatures for all orientations of the magnetic field in the crystal investigated are negative, attesting to the predominantly antiferromagnetic character of the exchange interactions. The effective magnetic moment of the Cu²⁺ ion is anisotropic and lies in the range from 1.054μ _B to 1.545μ _B. The magnetization depends linearly on magnetic field at T>10 K, whereas at temperatures below 10 K a discontinuity is observed at fields of the order of 40 kOe. At room temperature, electron magnetic resonance characterized by an almost isotropic g factor (g=2.165) is detected at 36.22 GHz. The exchange interactions in Cu₃B₂O₆ are analyzed on the basis of the Goodenough-Kanamori rules. The possibility of the establishment of a singlet magnetic state in the crystal is analyzed. Fiz. Tverd. Tela (St. Petersburg) 41, 677–679 (April 1999)     

On the spectrum of the hydrogen atom in an ultrastrong magnetic field

Various approaches to computing the energies of the ground state and excited levels of the hydrogen atom in an ultrastrong magnetic field B that considerably exceeds the field B _a = m _e ² e ³ c/ħ ³ ∼ 10⁹ G are considered. The effects of polarization of vacuum and anomalous magnetic moment of the electron on the position of the atomic levels are discussed. The vacuum polarization effects are negligibly weak for B < 10¹⁵ G but become significant in fields B ≫ 10¹⁶ G, in which these effects qualitatively modify the atomic spectrum in this range. The difference in the behaviors of the even and odd energy levels for B ≫ B _a is analyzed and the formulas for the energies of odd levels as a function of field B are refined.