Intrinsic anomalous scaling in a ferromagnetic thin film model

Recently, the interest on theoretical and experimental studies of dynamic properties of the magnetic domain wall (MDW) of ferromagnetic thin films with disorder placed in an external magnetic field has increased. In order to study global and local measurable observables, we consider the (1 + 1)-dimensional model introduced by Buceta and Muraca [Physica A 390, 4192 (2011)], based on rules of evolution that describe the MDW avalanches. From the values of the roughness exponents, global ζ, local ζ _loc, and spectral ζ _s , obtained from the global interface width, height-difference correlation function and structure function, respectively, recent works have concluded that the universality classes should be analyzed in the context of the anomalous scaling theory. We show that the model is included in the group of systems with intrinsic anomalous scaling (ζ ? 1.5, ζ _loc = ζ _s ? 0.5), and that the surface of the MDW is multi-affine. With these results, we hope to establish in short term the scaling relations that verify the critical exponents of the model, including the dynamic exponent z, the exponents of the distributions of avalanche-size τ and -duration α, among others.     

Charge-exchange resonances and restoration of Wigner’s supersymmetry in heavy and superheavy nuclei

Various facets of the question of whether Wigner’s supersymmetry [SU(4) symmetry] may be restored in heavy and superheavy nuclei are analyzed on the basis of a comparison of the results of calculations with experimental data. The energy difference between the giant Gamow–Teller resonance and the analog resonance (the difference of E _G and E _A) according to calculations based on the theory of finite Fermi systems is presented for the case of 33 nuclei for which experimental data are available. The calculated difference ΔE _G–A of E _G and E _A tends to zero in heavier nuclei, showing evidence of the restoration of Wigner’s SU(4) symmetry. Also, the isotopic dependence of the Coulomb energy difference between neighboring isobaric nuclei is analyzed within the SU(4) approach for more than 400 nuclei in the mass-number range of A = 5–244. The restoration of Wigner’s SU(4) symmetry in heavy nuclei is confirmed. It is shown that the restoration of SU(4) symmetry is compatible with the possible existence of the stability island in the region of superheavy nuclei.     

Evolution of spin susceptibility from the Pauli to Curie-Weiss type in strongly correlated Fermi systems

The magnetic properties of strongly correlated Fermi systems are studied within the framework of the fermioncondensation model—phase transition associated with the rearrangement of the Landau quasiparticle distribution, resulting in the appearance of a plateau at T=0 exactly in the Fermi surface of the single-particle excitation spectrum. It is shown that the Curie-Weiss term ～T^?1 appears in the expression for the spin susceptibility χ_ac(T) of the system after the transition point at finite temperatures. The behavior of χ_ac(T, H) as a function of temperature and static magnetic field H in the region where the critical fermion-condensation temperature T _f is close to zero is discussed. The results are compared with the available experimental data.     

Energy dependence of effective nucleon-nucleon interaction and position of the nucleon drip line

A semimicroscopic version of the self-consistent theory of finite Fermi systems is proposed. In this approach, the standard theory of finite Fermi systems is supplemented with relations that involve the external values of the invariant components of the Landau-Migdal amplitude and which follow from microscopic theory. The Landau-Migdal amplitude at the nuclear surface is expressed in terms of the off-shell T matrix for free nucleon-nucleon scattering at the energy E equal to the doubled chemical potential of the nucleus being considered. The strong energy dependence of the free T matrix at low E changes the properties of nuclei in the vicinity of the nucleon drip line. It is shown that, upon taking into account the energy dependence of the effective interaction, the neutron drip line is shifted considerably toward greater neutron-excess values. This effect is illustrated by considering the example of the tin-isotope chain.     

Production of Transuranium Nuclides in Pulsed Neutron Fluxes from Thermonuclear Explosions

The production of transuranium nuclides in pulsed neutron fluxes from thermonuclear explosions has been studied within the kinetic model of the astrophysical r-process taking into account the time dependence of external parameters and processes accompanying the beta decay of neutron-rich nuclei. Neutron fluxes depending on the time in the range of ~10^–6 s have been simulated within the developed adiabatic binary model. The probabilities of beta-delayed processes have been calculated within the microscopic theory of finite Fermi systems. The yields of transuranium nuclides Y(A) have been calculated for three experimental thermonuclear explosions Mike (Y_M), Par (Y_P), and Barbel (Y_B) (United States). The rms deviations of the calculations from experimental data are 91, 33, and 29% for Y_M, Y_P, and Y_B, respectively. These deviations are much smaller than those for other known calculations and are comparable with the proposed exponential approximation ensuring rms deviations of 56, 86.8, and 60.2% for Y_M, Y_P, and Y_B, respectively. The even–odd anomaly in the observed yields of heavy nuclei is explained by the dominant effect of processes accompanying the beta decay of heavy neutron-rich isotopes.     

Hyperfine interactions in Sc<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Y<Subscript>x</Subscript>Fe<Subscript>2</Subscript> cubic Laves alloys

Effects of hybridization of 3d bands of iron with 3d bands of scandium and 4d bands of yttrium in Sc_1?xY_xFe₂ cubic Laves alloys (0≤_x≤1) are studied by the nuclear magnetic resonance method. The concentration dependences of the lattice parameters a, saturation magnetization σ, and hyperfine fields at the ⁵⁷Fe, ⁴⁵Sc, and ⁸⁹Y nuclei—as well as the ²⁷Al impurity nuclei, whose atoms substitute iron atoms in the lattices of these alloys—are measured. The “local” and “induced” contributions to hyperfine fields at the ⁵⁷Fe nuclei are separated and the magnetic moments at iron atoms are estimated. It is found that the hybridization effect leads to the formation of magnetic moments at Sc and Y atoms (whose direction is opposite to the direction of the magnetic moment at iron atoms) and is responsible for the ferrimagnetic structure in Sc_1?xY_xFe₂ alloys.     

Behavior of Fermi systems approaching the fermion condensation quantum phase transition from the disordered phase

The behavior of Fermi systems that approach the fermion condensation quantum phase transition (FCQPT) from the disordered phase is considered. We show that the quasiparticle effective mass M* diverges as M* ∝ 1/¦x?x_FC¦, where x is the system density and x_FC is the critical point at which FCQPT occurs. Such behavior is of general form and takes place in both three-dimensional (3D) and two-dimensional (2D) systems. Since the effective mass M* is finite, the system exhibits the Landau Fermi liquid behavior. At ¦x? x_FC¦/x_FC?1, the behavior can be viewed as highly correlated, because the effective mass is large and strongly depends on the density. In the case of electronic systems, the Wiedemann-Franz law is valid and the Kadowaki-Woods ratio is preserved. Beyond the region ¦x–x_FC¦/x_FC?1, the effective mass is approximately constant and the system becomes a conventional Landau Fermi liquid.     

Mössbauer study of the modulated magnetic structure of FeVO<Subscript>4</Subscript>

Mössbauer spectroscopy is used to study the FeVO₄ multiferroic, which undergoes two magnetic phase transitions at T _N1 ≈ 22 K and T _N2 ≈ 15 K. The first transition (T _N1) is related to transformation from a paramagnetic state into a magnetically ordered state of a spin density wave, and the second transition (T _N2) is associated with a change in the type of the spatial magnetic structure of the vanadate. The electric field gradient tensor at ⁵⁷Fe nuclei is calculated to perform a crystal-chemical identification of the partial Mössbauer spectra corresponding to various crystallographic positions of Fe³⁺ cations. The spectra measured in the range T _N2 < T < T _N1 are analyzed on the assumption about amplitude modulation of the magnetic moments of iron atoms μ_Fe. The results of model intersection of the spectra recorded at T < T _N2 point to a high degree of anharmonicity of the helicoidal magnetic structure of the vanadate and to elliptic polarization of μ_Fe. These features are characteristic of type-II multiferroics. The temperature dependences of the hyperfine interaction parameters of ⁵⁷Fe nuclei that were obtained in this work are analyzed in terms of the Weiss molecular field model on the assumption of orbital contribution to the magnetic moments of iron cations.     

Electronic transport through a Majorana bound state coupled to a T-shaped quantum-dot system with Coulomb interaction

Using the Green’s function technique, we respectively investigate the electron transport properties of two spin components through the system of a T-shaped double quantum dot structure coupled to a Majorana bound state, in which only one quantum dot is connected with two metallic leads. We explore the interplay between the Fano effect and the MBSs for different dot-MBS coupling strength λ, dot-dot coupling strength t, and MBS-MBS coupling strength ε_M in the noninteracting case. Then the Coulomb interaction and magnetic field effect on the conductance spectra are investigated. Our results indicate that G_↓(ω) is not affected by the Majorana bound states, but a “0.5” conductance signature occurs in the vicinities of Fermi level of G_↑(ω). This robust property persists for a wide range of dot-dot coupling strength and dot-MBS coupling strength, but it can be destroyed by Coulomb interaction in quantum dots. By adjusting the size and direction of magnetic field around the quantum dots, the “0.5” conductance signature damaged by U can be restored. At last, the spin magnetic moments of two dots by applying external magnetic field are also predicted.     

Features of Electronic Structure of Intermetallic Compounds CeNi<Subscript>4</Subscript>M (M = Fe,Co, Ni,Cu)

The evolution of the electronic structure of CeNi₄M (M = Fe, Co, Ni, Cu) intermetallics depending on the type of nickel substitutional impurity is explored. We have calculated band structures of these compounds and considered options of substituting one atom in nickel 3d sublattice in both types of crystallographic positions: 2c and 3g. The analysis of total energy self-consistent calculations has shown that positions of 2c type are more energetically advantageous for single iron and cobalt impurities, whereas a position of 3g type is better for a copper impurity. The Cu substitutional impurity does not change either the nonmagnetic state of ions or the total density at the Fermi level states. Fe and Co impurities, on the contrary, due to their considerable magnetic moments, induce magnetization of 3d states of nickel and cause significant changes in the electronic state density at the Fermi level.     

Emergent nesting of the Fermi surface from local-moment description of iron-pnictide high-T<Subscript>c</Subscript> superconductors

We uncover the low-energy spectrum of a t-J model for electrons on a square lattice of spin-1 iron atoms with 3d _xz and 3d _yz orbital character by applying Schwinger-boson-slave-fermion mean-field theory and by exact diagonalization of one hole roaming over a 4 × 4 × 2 lattice. Hopping matrix elements are set to produce hole bands centered at zero two-dimensional (2D) momentum in the free-electron limit. Holes can propagate coherently in the t-J model below a threshold Hund coupling when long-range antiferromagnetic order across the d + = 3d _{(x + iy)z} and d ? = 3d _{(x ? iy)z} orbitals is established by magnetic frustration that is off-diagonal in the orbital indices. This leads to two hole-pocket Fermi surfaces centered at zero 2D momentum. Proximity to a commensurate spin-density wave (cSDW) that exists above the threshold Hund coupling results in emergent Fermi surface pockets about cSDW momenta at a quantum critical point (QCP). This motivates the introduction of a new Gutzwiller wavefunction for a cSDW metal state. Study of the spin-fluctuation spectrum at cSDW momenta indicates that the dispersion of the nested band of one-particle states that emerges is electron-type. Increasing Hund coupling past the QCP can push the hole-pocket Fermi surfaces centered at zero 2D momentum below the Fermi energy level, in agreement with recent determinations of the electronic structure of mono-layer iron-selenide superconductors.     

Effect of doping by boron,carbon, and nitrogen atoms on the magnetic and photocatalytic properties of anatase

The effect of doping of titanium dioxide with the anatase structure by boron, carbon, and nitrogen atoms on the magnetic and optical properties and the electronic spectrum of this compound has been investigated using the ab initio tight-binding linear muffin-tin orbital (TB-LMTO) band-structure method in the local spin density approximation explicitly including Coulomb correlations (LSDA + U) in combination with the semiempirical extended Hückel theory (EHT) method. The LSDA + U calculations of the electronic structure, the imaginary part of the dielectric function, the total magnetic moments, and the magnetic moments at the impurity atoms have been carried out. The diagrams of the molecular orbitals of the clusters Ti₃ X (X = B, C, N) have been calculated and the pseudo-space images of the molecular orbitals of the clusters have been constructed. The effect of doping on the nature and origin of photocatalytic activity in the visible spectral range and the specific features of the generation of ferromagnetic interactions in doped anatase have been discussed based on the analysis of the obtained data. It has been shown that, in the sequence TiO_{2 ? y} N _y → TiO_{2 ? y} C _y → TiO_{2 ? y} B _y (y = 1/16), the photocatalytic activity can increase with the generation of electronic excitations with the participation of impurity bands. The calculated magnetic moments for boron and nitrogen atoms are equal to 1 μ_B, whereas the impurity carbon atoms are nonmagnetic.     

The influence of a weak magnetic field in the Renormalization-Group functions of (2 + 1)-dimensional Dirac systems

The experimental observation of the renormalization of the Fermi velocity v _F as a function ofdoping has been a landmark for confirming the importance of electronic interactions ingraphene. Although the experiments were performed in the presence of a perpendicularmagnetic field B, the measurements are well described by arenormalization-group (RG) theory that did not include it. Here we clarify this issue, forboth massive and massless Dirac systems, and show that for the weak magnetic fields atwhich the experiments are performed, there is no change in the renormalization-groupfunctions. Our calculations are carried out in the framework of the Pseudo-quantumelectrodynamics (PQED) formalism, which accounts for dynamical interactions. We includeonly the linear dependence in B, and solve the problem using two differentparametrizations, the Feynman and the Schwinger one. We confirm the results obtainedearlier within the RG procedure and show that, within linear order in the magnetic field,the only contribution to the renormalization of the Fermi velocity for the massive casearises due to electronic interactions. In addition, for gapped systems, we observe arunning of the mass parameter.     

Hyperfine-structure measurements on Dy161 and Dy163

In an atomic beam magnetic resonance experiment the hyperfine interaction constantsA andB of the⁵ I ₈ groundstate of Dy¹⁶¹ and Dy¹⁶³ were found to be Dy¹⁶¹:A=?(115.8±1)MHz, Dy¹⁶³:A=(162.9±0.6)MHz,B=(1102±15)MHz,B=(1150±20)MHz. Using an effective value for 〈r^?3〉, the magnetic moments and electric quadrupole moments of the Dy¹⁶¹ and Dy¹⁶³ nuclei were calculated to be Dy¹⁶¹:μ _I=?(0.47±0.09) n.m., Dy¹⁶³:μ _I=(0.66±0.13)n.m.,Q=(2.36±0.4)barns,Q=(2.46±0.4)barns.     

Stable and Unstable Vortex Knots in a Trapped Bose Condensate

The dynamics of a quantum vortex toric knot T_P,Q and other analogous knots in an atomic Bose condensate at zero temperature in the Thomas–Fermi regime is considered in the hydrodynamic approximation. The condensate has a spatially inhomogeneous equilibrium density profile ρ(z, r) due to the action of an external axisymmetric potential. It is assumed that z_*= 0, r_*= 1 is the point of maximum of function rρ(z, r), so that δ(rρ) ≈ –(α–)z²/2–(α + )(δr)²/2 for small z and δr. The geometrical configuration of a knot in the cylindrical coordinates is determined by a complex 2πP-periodic function A(?, t) = Z(?, t) + i[R(?, t))–1]. When |A| ? 1, the system can be described by relatively simple approximate equations for P rescaled functions \({W_n}(\varphi ) \propto A(2\pi n + \varphi ):i{W_{n,t}} = - ({W_{n,\varphi \varphi }} + \alpha {W_n} - \in W_n^*)/2 - \sum\nolimits_{j \ne n} {1/(W_n^* - W_j^*)} \). For = 0, examples of stable solutions of type W _n = θ _n (?–γt)exp(–iωt) with a nontrivial topology are found numerically for P = 3. In addition, the dynamics of various unsteady knots with P = 3 is modeled, and the tendency to the formation of a singularity over a finite time interval is observed in some cases. For P = 2 and small ≠ 0, configurations of type W₀–W₁ ≈ B₀exp(iζ) + C(B₀, α)exp(–iζ) + D(B₀, α)exp(3iζ), where B₀ > 0 is an arbitrary constant, ζ = k₀?–Ω₀t + ζ0, k₀ = Q/2, and Ω₀ = (–α)/2–2/B₀², which rotate about the z axis, are investigated. Wide stability regions for such solutions are detected in the space of parameters (α, B₀). In unstable zones, a vortex knot may return to a weakly excited state.     

First principles study on magnetic properties in ZnS doped with palladium

The electronic structures and magnetic properties in zinc-blende structure ZnS doped with nonmagnetic noble metal palladium have been investigated by means of density functional theory (DFT) calculations employing the generalised gradient approximation (GGA) and the GGA plus Hubbard U (GGA + U). Both the GGA and GGA + U methods demonstrate half-metallicity in Pd-doped ZnS with total magnetic moments of about 2.0μ _B per supercell. The half-metallic ferromagnetism stems from the hybridisation between Pd-4d and S-3p states and could be attributed to a double-exchange mechanism. These results suggest a recipe for obtaining a promising dilute magnetic semiconductor by doping nonmagnetic 4d elements in ZnS matrix.     

New Analytical Solution of the Equilibrium Ampere’s Law Using the Walker’s Method: a Didactic Example

This work aims to demonstrate the analytical solution of the Grad-Shafranov (GS) equation or generalized Ampere’s law, which is important in the studies of self-consistent 2.5-D solution for current sheet structures. A detailed mathematical development is presented to obtain the generating function as shown by Walker (RSPSA 91, 410, 1915). Therefore, we study the general solution of the GS equation in terms of the Walker’s generating function in details without omitting any step. The Walker’s generating function g(ζ) is written in a new way as the tangent of an unspecified function K(ζ). In this trend, the general solution of the GS equation is expressed as exp(??2Ψ) =?4|K ^′(ζ)|²/cos²[K(ζ) ? K(ζ ^?)]. In order to investigate whether our proposal would simplify the mathematical effort to find new generating functions, we use Harris’s solution as a test, in this case K(ζ) = arctan(exp(i ζ)). In summary, one of the article purposes is to present a review of the Harris’s solution. In an attempt to find a simplified solution, we propose a new way to write the GS solution using g(ζ) = tan(K(ζ)). We also present a new analytical solution to the equilibrium Ampere’s law using g(ζ) = cosh(b ζ), which includes a generalization of the Harris model and presents isolated magnetic islands.     

The quadrupole moments of some even–even nuclei around the mass of <Emphasis Type="Italic">A</Emphasis> ~ 80: <Superscript>68−80</Superscript>Ge on the neighborhood of <Superscript>76−84</Superscript>Kr and <Superscript>76−84</Superscript>Se isotopes

We have carried out the calculation of the quadrupole moments Q(2₁⁺) and electromagnetic transition rates B(E2) of some levels within the framework of the interacting boson model for even-mass Ge nuclei. The presented predictions of the quadrupole moments and B(E2) ratios for Ge nuclei are compared with the results of some previous experimental and theoretical ones along with those of the neighboring Kr and Se isotopes and then it was seen that they agree well with the previous experimental and theoretical ones.     

Transition from non-fermi liquid behavior to Landau–Fermi liquid behavior induced by magnetic fields

We show that a strongly correlated Fermi system with a fermion condensate which exhibits strong deviations from Landau–Fermi liquid behavior is driven into the Landau–Fermi liquid by applying a small magnetic field B at temperature T=0. This field-induced Landau–Fermi liquid behavior provides constancy of the Kadowaki–Woods ratio. A re-entrance into the strongly correlated regime is observed if the magnetic field B decreases to zero; the effective mass M* then diverges as \(M^* \propto {1 \mathord{\left/ {\vphantom {1 {\sqrt B }}} \right. \kern-\nulldelimiterspace} {\sqrt B }}\). At finite temperatures, the strongly correlated regime is restored at some temperature \(T^* \propto \sqrt B \). This behavior is of a general form and takes place in both three-dimensional and two-dimensional strongly correlated systems. We demonstrate that the observed \({1 \mathord{\left/ {\vphantom {1 {\sqrt B }}} \right. \kern-\nulldelimiterspace} {\sqrt B }}\) divergence of the effective mass and other specific features of heavy-fermion metals are accounted for by our consideration.     

From the Bose-Einstein to fermion condensation

The appearance of the fermion condensation, which can be compared to the Bose-Einstein condensation, in different Fermi liquids is considered; its properties are discussed; and a large amount of experimental evidence in favor of the existence of the fermion condensate (FC) is presented. We show that the appearance of FC is a signature of the fermion condensation quantum phase transition (FCQPT), which separates the regions of normal and strongly correlated liquids. Beyond the FCQPT point, the quasiparticle system is divided into two subsystems, one containing normal quasiparticles and the other, FC, localized at the Fermi level. In the superconducting state, the quasiparticle dispersion in systems with FC can be represented by two straight lines, characterized by effective masses M _FC ^* and M _L ^* and intersecting near the binding energy E₀, which is of the order of the superconducting gap. The same quasiparticle picture and the energy scale E₀ persist in the normal state. We demonstrate that fermion systems with FC have features of a “quantum protectorate” and show that strongly correlated systems with FC, which exhibit large deviations from the Landau Fermi liquid behavior, can be driven into the Landau Fermi liquid by applying a small magnetic field B at low temperatures. Thus, the essence of strongly correlated electron liquids can be controlled by weak magnetic fields. A reentrance into the strongly correlated regime is observed if the magnetic field B decreases to zero, while the effective mass M* diverges as \(M^ * \propto {1 \mathord{\left/ {\vphantom {1 {\sqrt B }}} \right. \kern-\nulldelimiterspace} {\sqrt B }}\). The regime is restored at some temperature \(T^ * \propto \sqrt B \). The behavior of Fermi systems that approach FCQPT from the disordered phase is considered. This behavior can be viewed as a highly correlated one, because the effective mass is large and strongly depends on the density. We expect that FCQPT takes place in trapped Fermi gases and in low-density neutron matter, leading to stabilization of the matter by lowering its ground-state energy. When the system recedes from FCQPT, the effective mass becomes density independent and the system is suited perfectly to be conventional Landau Fermi liquid.