Investigation of three-particle spin correlations during critical scattering of polarized neutrons from a nickel single crystal

The critical small-angle scattering of polarized neutrons from spin fluctuations in a nickel single crystal with a special inclined geometry of the magnetic field has been studied. The method of inclined geometry makes it possible to investigate not only two-particle spin correlations but also three-particle spin correlations that determine the polarization-dependent contribution to scattering, which is asymmetric with respect to the momentum transfer q. This contribution depends on the momentum transfer q as 1/(q ² + ξ^?2)^5/2, where f is the neutron scattering correlation length; it linearly increases with an increase in the magnetic field H in the low-field range and then reaches saturation. The results obtained are in good agreement with the similarity theory.     

First-order reorientation transition of the flux-line lattice in CaAlSi

The flux-line lattice in CaAlSi has been studied by small-angle neutron scattering. A well-defined hexagonal flux-line lattice is seen just above H(c1) in an applied field of only 54 Oe. A 30° reorientation of this vortex lattice has been observed in a very low field of 200 Oe. This reorientation transition appears to be first-order and could be explained by nonlocal effects. The magnetic field dependence of the form factor is well-described by a single penetration depth of λ=1496(1) ? and a single coherence length of ξ=307(1) ? at 2 K. At 1.5 K, the penetration depth anisotropy is γ(λ)=2.7(1), with the field applied perpendicular to the c axis, and agrees with the coherence length anisotropy determined from critical field measurements.     

Spatially ordered arrays of magnetic nanowires: Polarized-neutron scattering investigation

The structure and magnetic properties of magnetically ordered arrays of magnetic nanowires formed on the basis of porous aluminum oxide films have been investigated by the small-angle polarized-neutron scattering method. Small-angle scattering intensity patterns exhibit several diffraction maxima (up to the third reflection order), which correspond to scattering from the highly ordered porous structure of the matrix and on the hexagonal packing of magnetic nanowires. The observed reflections are imposed on noticeable diffuse scattering associated with the defects of the structure. A theoretical solution is obtained for describing neutron diffraction in the dynamical limit on the superstructure of magnetic nanowires incorporated into the diamagnetic matrix. Several contributions to scattering that have been analyzed are the nonmagnetic (nuclear) contribution, the magnetic contribution depending on a magnetic field, and the nuclear-magnetic interference indicating the correlation between the magnetic and nuclear structures. A detailed pattern of the remagnetization of an ordered array of the magnetic nanowires has been obtained and it has been shown that polarized neutron scattering provides information inaccessible by the standard magnetometric methods.     

坡密子和胶子球

讨论了高能强子 -强子散射过程中的坡密子以及坡密子的 QCD内容 .认为坡密子有可能就是具有量子数 IG=0 + ,JPC=2 + +的张量胶子球 ξ( 2 2 30 ) .用雷其化胶子球模型计算了高能质子 -质子散射截面和坡密子 -核子的耦合参数 β.理论结果与实验的要求一致. The pomeron in high energy hadron hadron scattering as well as the QCD nature of the pomeron are discussed. We claimed that the pomeron may be the tenser glueball ξ(2 230) with quantum number I G =0 +, J PC =2 ++ . Under this reggeized glueball model the cross section of high energy proton proton scattering and the coupling parameter of the pomeron nucleon, β , are calculated. The theoretical results of the present model are in good agreement with experimental data.     

Problems of Deep Inelastic Lepton-Nucleus Interaction

The deep inelastic scattering of electrons (muons) and neutrinos on the nuclei and the process of lepton pair production in hadron-nucleus collisions are considered. The expressions for the corresponding differential cross-sections are derived provided the final lepton and the spectator fragment of the initial nucleus are detected in coincidence. The structure functions of the processes under consideration are analysed by the principle of automodelity. Some scale-invariant regularities are established for them. In the framework of “light front” formalism for many-body systems the relations of these structure functions to the usual structure functions of the deep inelastic lepton hadron interaction are obtained. A hypothesis is put forward on the scale invariance of structure functions with respect to the ξ-variable which is some complicated dimensionless combination of kinematic invariants.     

Resolving magnetic and chemical correlations in CoPtCr films using soft X-ray resonant scattering

Resonant small-angle scattering at the 2p levels of 3d transition elements strongly enhances scattering from both magnetic and chemical structure in the plane of thin films, as recently demonstrated for Co/Pt multilayers having perpendicular anisotropy. Here this resonant enhancement is demonstrated for CoPtCr films having in-plane magnetic anisotropy. A simple formalism describing the spectral dependence of the kinematical scattering provides a means to distinguish between magnetic and charge scattering and to probe the chemical segregation processes yielding charge scattering, thereby providing new information about this structure. It is found that correlation lengths of magnetic scattering are roughly 5 times larger than those for chemical scattering in the as-deposited CoPtCr film studied, consistent with significant exchange-coupling between polycrystalline grains.     

Existence of Tensor Glueball ξ(2230) and Its Mass, Spin, and Decay Width

In order to solve the current experimental controversy on the existence of the tensor glueball ξ(2230), we examine whether the conclusion from Seth's experimental measurement, which rejects existence of ξ(2230), is reliable. We claim that the non-observation of the resonance structure by Seth is not a sound ground for rejecting the existence of ξ(2230) but it may just indicate that ξ(2230) has a broad width. We also study the tensor glueball properties: the mass, spin, and decay width. Our theoretical predictions of the mass and the spin of the ξ(2230) using QCD sum rule are about 2.23 GeV and J=2, respectively. Our theoretical results also evidently show that the ξ(2230) must have a total decay width of about 100 MeV, which is much broader than the reported 20 MeV but a small partial decay width of 2 MeV into pp decay channel.     

Thermodynamics of a gas of deconfined bosonic spinons in two dimensions

We consider the quantum phase transition between a Néel antiferromagnet and a valence-bond solid (VBS) in a two-dimensional system of S = 1/2 spins. Assuming that the excitations of the critical ground state are linearly dispersing deconfined spinons obeying Bose statistics, we derive expressions for the specific heat C and the magnetic susceptibility χ at low temperature T in terms of a correlation length ξ(T). Comparing with quantum Monte Carlo results for the J-Q model, which is a candidate for a deconfined Néel-VBS transition, we obtain an almost perfect consistency between C, χ, and ξ. The corresponding expressions for magnon (triplet) excitations are not internally consistent, however, lending strong support for spinon excitations in the J-Q model.     

On the penetration of the magnetic field into a superconductor

It is known that in superconductors the exponential decay of the magnetic field is an approximation, which breaks down if the dimension of a Cooper pair ξ _f is of the order or smaller than the London penetration depth δ. The appearance of a nonlocal relation between current and field yields deviations from the exponential decay especially a sign reversal of the field at a certain distance. This sign reversal is connected with a change: of the surface energy in superconductors and of the structure of fluxoids together with their interaction. In this paper we present results on the decay of magnetic field which is calculated from the exact BCS-integral-kernel for weak fields. As a result, the nonlocal effects in the framework of BCS-theory can be described in good approximation by the ratio of the London penetration depth δ(T, l) and the dimension of Cooper pairs ξ _f (T, l). The evaluations show, that one has still sign reversal, i.e. large nonlocal effects, in Type II superconductors with a κ(T _c )?,1.6. It should be mentioned that the limit κ?1.6 coincides roughly with the experimentally observed region of attraction of fluxoids. In addition results on the penetration depths are summarized.     

Effect of double nuclear scattering on nuclear-magnetic interference in experiment with small-angle diffraction of polarized neutrons

An experiment on small-angle polarized-neutron diffraction by a two-dimensional spatially ordered array of nickel nanowires embedded in a porous anodic alumina matrix is discussed. The contributions of nonmagnetic (nuclear) structures and nuclear magnetic interference indicating the correlation between magnetic and nuclear structures are discussed. Magnetic scattering is two orders of magnitude smaller than nuclear scattering and, hence, turns out to be weakly distinguishable. The ordered magnetic composite nanostructure of a sample leads to strong interaction between the neutron wave and the structure itself, which, in turn, implies a twofold (miltiple scattering) nuclear scattering process. Nuclear magnetic interference scattering must be analyzed allowing for twofold scattering conditions, which substantially distorts the intensity distribution of the interference contribution of first-order diffraction peaks.     

The growth of soft magnetic FeNiN thin films under different experimental procedures

FeNiN thin films with good soft magnetic properties were synthesized on Si (1 0 0) substrates at 473 K by RF magnetron sputtering. The dependence of phase structure and magnetic properties on nitrogen partial pressure, nickel concentrations, film thickness and substrate temperature were systematically investigated. The phase evolution from α-(Fe,Ni)N to ξ-(Fe,Ni)₂N with increase of nitrogen partial pressure was seen. The addition of Ni caused FeNiN films to turn from BCC structure to FCC structure. Clear reproducible striped domains appeared at the film surfaces when X_Ni=19.6%, which is explained by the high enough perpendicular anisotropy and the small stress in the film. All films show smooth surfaces and good soft magnetic properties compared to corresponding FeN compounds. The magnetic properties depended dramatically on the phase structure. Optimum soft magnetic properties with H_C of <1 Oe are obtained between 5.0%?X_Ni?10.0%.     

Polar exit angle distributions of slow H<Superscript>+</Superscript> ions,related to the presence of a regular domain structure,calculated within the diffuse scattering approximation upon interaction of ions with the sample surface

The angular distributions of slow H ions scattered from the surface of a magnetic film with a stripe domain structure have been calculated. The calculations were performed within the models of specular and diffuse scattering upon collisions of ions with surface. It is shown that the magnetic fields of the stripe domain structure block the ions scattered at small exit angles. It is established that, within the more adequate model of diffuse scattering, the anisotropy of interaction of ions with the magnetic field of the stripe structure manifests itself in a wider angular range.     

Powder structure of magnetic nanoparticles with a substituted pyrrole copolymer shells according to small-angle neutron scattering

Powders of magnetic nanoparticles coated by biocompatible block copolymers (substituted pyrroles) are investigated by small-angle neutron scattering. It is found that the structure of the final precipitates depends on the type of stabilizing shell in the initial magnetic fluids. When dodecylbenzene sulfonic acid is used, separate polydisperse particles with a radius of gyration of 3–5 nm and an irregular surface (fractal dimension of 2.24) are observed in the final samples. For systems with lauric acid, additional scattering from a quasicrystalline structure with a characteristic correlation length of about 10 nm can be seen in the experimental spectra. The difference in the organization of the structure of the studied powders is related to a different polymer coating rate on the surface of the magnetic nanoparticles, which depends on the sorption properties of surfactants in the initial magnetic fluids.     

Magnetic inverted photonic crystals: A polarized neutron scattering study

This work is devoted to a small-angle polarized neutron scattering study of the structure and magnetic properties of nickel inverted photonic crystals. Depending on the intensity of the small-angle scattering, diffraction maximums up to fourth-order reflections, which correspond to scattering from the highly ordered structures of the test samples, are observed. Several contributions to the scattering are analyzed: a nuclear contribution; a magnetic contribution; a contribution depending on an external magnetic field; and a nuclear magnetic interference, which shows a correlation between magnetic and nuclear structures. It is found that a magnetization reversal process, which was represented by a standard hysteresis curve, for weak fields was accompanied by both domain formation and coherent magnetization rotation from the field direction to directions caused by geometric structure peculiarities.     

Measurement of analyzing power for proton-carbon elastic scattering in the coulomb-nuclear interference region with a 22-GeV/c polarized proton beam

The analyzing power for proton-carbon elastic scattering in the Coulomb-nuclear interference region of momentum transfer, 9.0x10(-3)<-t<4.1x10(-2) (GeV/c)(2), was measured with a 21.7 GeV/c polarized proton beam at the Alternating Gradient Synchrotron of Brookhaven National Laboratory. The ratio of hadronic spin-flip to nonflip amplitude, r(5), was obtained from the analyzing power to be Rer(5)=0.088+/-0.058 and Imr(5)=-0.161+/-0.226.     

Giant magnetoresistance in an electrochemically synthesized regimented array of nickel quantum dots

Giant magnetoresistance (GMR) due toremotespin dependent scattering of electrons has been observed in an electrochemically synthesized structure consisting of a two-dimensional, quasi-periodic array of nickel dots (diameter ∼100 Å) overlayed with a thin copper layer. Current flows exclusively in the copper layer, but the electrons scatter from the magnetic moments on the remote, underlying nickel quantum dots. Since the scattering cross-section depends on the magnetization of the dots, the resistance of the structure can be altered with a magnetic field which then gives rise to the GMR. The magnetoresistance is about 3% of the zero-field resistance up to a magnetic flux density of 2 tesla at room temperature.     

Magnetic properties of cobalt nanowires: Study by polarized SANS

Structural and magnetic properties of two-dimensional spatially ordered system of ferromagnetic cobalt nanowires embedded into Al₂O₃ matrix have been studied using polarized small-angle neutron scattering. A comprehensive analysis of contributions to the scattering intensity was carried out, including nonmagnetic (nuclear) contribution, magnetic contribution depending on the magnetic field, and nuclear-magnetic interference indicating the correlation between the magnetic and nuclear structures. Experiments have revealed an anomalously low value of the magnetic contribution as compared to the nuclear one. This behavior is interpreted in terms of low coherence of the magnetic structure caused by the anisotropy of Co crystallites as compared with the large coherency of nuclear structure of nanowires.     

Long-range antiferromagnetic order in CeCu5.5Au0.5

The magnetic ordering previously discovered in CeCu_6–xAu_x heavy-fermion alloys is shown to be of long-range antiferromagnetic type by elastic neutron scattering performed on a polycrystalline sample. The data are compatible with an incommensurate wave vector (0.17, 0, 0.514). Although a definite assignment needs a single-crystal study, the magnetic structure is clearly different from the type of magnetic correlations in pure CeCu₆ found in inelastic scattering.     

Visualization of the domain structure of ferromagnetic films using the magnetochemical effect

Iron film surfaces have been studied after their chemical treatment in a magnetic field. The chemical treatment of a metal leads to the appearance of a relief image that is interpreted as a “photograph” of magnetic scattering fields. The morphology of the relief image formed is shown to correlate with the domain structure of a magnetic film. The magnetochemical effect revealed allows the visualization of the dependence of the scattering field distribution at the sample surface on external magnetic field.