Evidence for non-Dzyaloshinskii–Moriya ferromagnetism in epitaxial BiFeO₃ films

BiFeO₃ films have been prepared by dc magnetron sputtering on LaAlO₃ (001) single-crystalline substrate. X-ray diffraction analysis and high-resolution electron-microscopy study reveal that the films have a highly coriented orthorhombic crystal structure. It was found that the magnetic properties of the BiFeO₃ films are typical for the ensemble of interacting superparamagnetic clusters rather than for the Dzyaloshinskii–Moriya weak ferromagnet. Appearance of the extrinsic nanoscale superparamagnetic clusters is explained by the oxygen deficiency in certain regions of the film, where the ferromagnetic ordering is realized through the double-exchange mechanism by Zener

Two-particle BoseEinstein correlations in pp collisions at √s = 0.9 and 7 TeV measured with the ATLAS detector

The paper presents studies of Bose–Einstein Correlations (BEC) for pairs of like-sign charged particles measured in the kinematic range pT > 100 MeV and |η| <2.5 in proton–proton collisions at centre-of-mass energies of 0.9 and 7 TeV with the ATLAS detector at the CERN Large Hadron Collider. The integrated luminosities are approximately 7 μb−1, 190 μb−1 and 12.4 nb-1 for 0.9 TeV,7 TeV minimum-bias and 7 TeV high-multiplicity data samples, respectively. The multiplicity dependence of the BEC parameters characterizing the correlation strength and the correlation source size are investigated for charged-particle multiplicities of up to 240. A saturation effect in the multiplicity dependence of the correlation source size parameter is observed using the high-multiplicity 7 TeV data sample. The dependence of the BEC parameters on the average transverse momentum of the particle pair is also investigated

Evidence for Griffiths phase in multiferroic BiMnO₃ and BiFe₀.₅Mn₀.₅O₃ films

Microstructure and magnetic properties of the BiMnO₃ and BiFe₀.₅Mn₀.₅O₃ films, prepared by the rf magnetron sputtering on LaAlO₃ (001) single-crystalline substrate, have been investigated. The selected-area electron diffraction analysis allows us to indentify the crystal structure of the BiMnO₃ film as an orthorhombic one while the BiFe₀.₅Mn₀.₅O₃ film has a hexagonal lattice symmetry. The high-resolution electron microscopy study reveals the presence of strip-domain phase with a periodic spacing of about 3c in both films. The magnetic measurements show that in addition to the basic paramagnetic phase, the films manifest the Griffiths phase behavior in a wide temperature range. We argue that the observed weak ferromagnetism is provided by an appearance of the strip-domain layered inclusions rather than the intrinsic physical origin of the films

Origin of an enhanced colossal magnetoresistance effect in epitaxial Nd₀.₅₂Sr₀.₄₈MnO₃ thin films

Nd₀.₅₂Sr₀.₄₈MnO₃ films with the different thickness have been prepared by dc magnetron sputtering on LaAlO₃ (001) single-crystalline substrates. A decrease of the film thickness leads to a significant suppression of the ferromagnetic (FM) ordering and the Curie point becomes below the antiferromagnetic (AFM) transition temperature. As this take place, a huge rise of the magnetoresistance ratio from 400 to 60 000% at an applied magnetic field of 5 T is observed. We consider that this new kind of the enhanced colossal magnetoresistance effect is originated from the FM/AFM competition and the collapse of the charge-ordered state at high magnetic field rather than through the regular double-exchange mechanism

Two-dimensional growth, anisotropic polaron transport and magnetic phase segregation in epitaxial Nd₀.₅₂Sr₀.₄₈MnO₃ films

Nd₀.₅₂Sr₀.₄₈MnO₃ films have been prepared by dc magnetron sputtering on LaAlO₃ (001) and SrTiO₃ (011) single-crystalline substrates with an additional annealing for the lattice strain relaxation. Even though that the Nd₀.₅₂Sr₀.₄₈MnO₃ films were deposited simultaneously on different substrates at the same deposition rate they differ in the thickness by≃2 . The observed difference in the thickness is explained by the twodimensional (layer-by-layer) growth of film rather than a difference in the growth rate, controlled by the crystal orientation of substrate. The analysis of the optical and transport properties reveals that the observed anisotropy in the polaron motion is governed by a strong anisotropy of the trapping energy rather than the polaron formation one. It was shown that the deposited Nd₀.₅₂Sr₀.₄₈MnO₃ films manifest a magnetic behavior typical for twophases magnetic systems and must be considered as an assembly of interacting magnetic clusters

Search for a heavy Standard Model Higgs boson in the channel H→ZZ→l+l−qqˉH\rightarrow ZZ\rightarrow l^{+}l^{-} q\bar{q} using the ATLAS detector

A search for a heavy Standard Model Higgs boson decaying via H->ZZ->llqq, where l=e,mu, is presented. The search is performed using a data set of pp collisions at sqrt(s)=7 TeV, corresponding to an integrated luminosity of 1.04 fb^-1 collected in 2011 by the ATLAS detector at the CERN LHC collider. No significant excess of events above the estimated background is found. Upper limits at 95% confidence level on the production cross section (relative to that expected from the Standard Model) of a Higgs boson with a mass in the range between 200 and 600 GeV are derived. Within this mass range, there is at present insufficient sensitivity to exclude a Standard Model Higgs boson. For a Higgs boson with a mass of 360 GeV, where the sensitivity is maximal, the observed and expected cross section upper limits are factors of 1.7 and 2.7, respectively, larger than the Standard Model prediction.Comment: 11 pages plus author list (26 pages total), 4 figures, 1 table, final version to appear in Physics Letters

Charged-particle multiplicities in <i>pp</i> interactions at &#8730;s = 900 GeV measured with the ATLAS detector at the LHC

The first measurements from proton–proton collisions recorded with the ATLAS detector at the LHC are presented. Data were collected in December 2009 using a minimum-bias trigger during collisions at a centre-of-mass energy of 900 GeV. The charged-particle multiplicity, its dependence on transverse momentum and pseudorapidity, and the relationship between mean transverse momentum and charged-particle multiplicity are measured for events with at least one charged particle in the kinematic range |η|&#60;2.5 and pT&#62;500 MeV. The measurements are compared to Monte Carlo models of proton–proton collisions and to results from other experiments at the same centre-of-mass energy. The charged-particle multiplicity per event and unit of pseudorapidity at η=0 is measured to be1.333&#177;0.003(stat.)&#177;0.040(syst.), which is 5–15% higher than the Monte Carlo models predict

Search for Diphoton Events with Large Missing Transverse Energy in 7 TeV Proton-Proton Collisions with the ATLAS Detector

A search for diphoton events with large missing transverse energy is presented. The data were collected with the ATLAS detector in proton-proton collisions at √s=7  [square root of s=7] TeV at the CERN Large Hadron Collider and correspond to an integrated luminosity of 3.1  pb-1 [pb superscript -1]. No excess of such events is observed above the standard model background prediction. In the context of a specific model with one universal extra dimension with compactification radius R and gravity-induced decays, values of 1/R<729  GeV are excluded at 95% C. L., providing the most sensitive limit on this model to date.United States. Dept. of EnergyNational Science Foundation (U.S.

Measurement of the isolated diphoton cross section in pp collisions at sqrt(s) = 7 TeV with the ATLAS detector

15 pages plus author list (27 pages total), 9 figures, 2 tables, submitted to Phys. Rev. DThe ATLAS experiment has measured the production cross-section of events with two isolated photons in the final state, in proton-proton collisions at sqrt(s) = 7 TeV. The full data set acquired in 2010 is used, corresponding to an integrated luminosity of 37 pb-1. The background, consisting of hadronic jets and isolated electrons, is estimated with fully data-driven techniques and subtracted. The differential cross-sections, as functions of the di-photon mass, total transverse momentum and azimuthal separation, are presented and compared to the predictions of next-to-leading-order QCD

Measurement of the isolated diphoton cross-section in pp collisions at sqrt(s) = 7 TeV with the ATLAS detector

The ATLAS experiment has measured the production cross-section of events with two isolated photons in the final state, in proton-proton collisions at sqrt(s) = 7 TeV. The full data set acquired in 2010 is used, corresponding to an integrated luminosity of 37 pb^-1. The background, consisting of hadronic jets and isolated electrons, is estimated with fully data-driven techniques and subtracted. The differential cross-sections, as functions of the di-photon mass, total transverse momentum and azimuthal separation, are presented and compared to the predictions of next-to-leading-order QCD.Comment: 15 pages plus author list (27 pages total), 9 figures, 2 tables, final version to appear in Physical Review