P. Link

Antiferromagnetic ordering and structural phase transition in Ba2Fe2As2 with Sn incorporated from the growth flux

Neutron diffraction experiments have been carried out on a Sn-flux grown BaFe2As2 single crystal, the parent compound of the A-122 family of FeAs-based high-Tc superconductors. A tetragonal to orthorhombic structural phase transition and a three dimensional long-range antiferromagnetic ordering of the iron moment, with a unique magnetic propagation wavevector k = (1, 0, 1), have been found to take place at ~90 K. The magnetic moments of iron are aligned along the long a axis in the low temperature orthorhombic phase (Fmmm with b<a<c). Our results thus demonstrate that the magnetic structure of BaFe2As2 single crystal is the same as those in other A-122 iron pnictides compounds. We argue that the tin incorporation in the lattice is responsible for a smaller orthorhombic splitting and lower Neel temperature T_N observed in the experiment.

Magnetic-Field-Induced Soft-Mode Quantum Phase Transition in the High-Temperature Superconductor La1:855Sr0:145CuO4: An Inelastic Neutron-Scattering Study

J. Chang, N. B. Christensen, 2, 3 Ch. Niedermayer, K. Lefmann, 3 H. M. Rønnow, 4 D. F. McMorrow, A. Schneidewind, 7 P. Link, A. Hiess, M. Boehm, R. Mottl, S. Pailhés, N. Momono, M. Oda, M. Ido, and J. Mesot 4 Laboratory for Neutron Scattering, ETH Zurich and PSI Villigen, CH-5232 Villigen PSI, Switzerland Materials Research Department, Risø National Laboratory for Sustainable Energy, DK-4000 Roskilde, Denmark Nano-Science Center, Niels Bohr Institute, University of Copenhagen, DK-2100 Copenhagen, Denmark Laboratory for Quantum Magnetism, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland London Centre for Nanotechnology and Department of Physics and Astronomy, University College London, London, UK Institut für Festkörperphysik, Technische Universität Dresden, D-01062 Dresden, Germany Forschungsneutronenquelle Heinz-Maier-Leibnitz (FRM-II), TU München, D-85747 Garching, Germany Institut Laue-Langevin, BP 156, F-38042 Grenoble, France Department of Physics, Hokkaido University Sapporo 060-0810, Japan

Helimagnon Bands as Universal Excitations of Chiral Magnets

MnSi is a cubic compound with small magnetic anisotropy, which stabilizes a helimagnetic spin spiral that reduces to a ferromagnetic and antiferromagnetic state in the long- and short-wavelength limit, respectively. We report a comprehensive inelastic neutron scattering study of the collective magnetic excitations in the helimagnetic state of MnSi. In our study we observe a rich variety of seemingly anomalous excitation spectra, as measured in well over twenty different locations in reciprocal space. Using a model based on only three parameters, namely the measured pitch of the helix, the measured ferromagnetic spin wave stiffness and the amplitude of the signal, as the only free variable, we can simultaneously account for \textit{all} of the measured spectra in excellent quantitative agreement with experiment. Our study identifies the formation of intense, strongly coupled bands of helimagnons as a universal characteristic of systems with weak chiral interactions.

Normal-State Hourglass Dispersion of the Spin Excitations in FeSexTe1-x

We use cold neutron spectroscopy to study the low-energy spin excitations of superconducting (SC) FeSe0.4Te0.6 and essentially nonsuperconducting (NSC) FeSe0.45Te0.55. In contrast with BaFe2-x(Co,Ni)xAs2, where the low-energy spin excitations are commensurate both in the SC and normal state, the normal-state spin excitations in SC FeSe0.4Te0.6 are incommensurate and show an hourglass dispersion near the resonance energy. Since similar hourglass dispersion is also found in the NSC FeSe0.45Te0.55, we argue that the observed incommensurate spin excitations in FeSe(1-x)Tex are not directly associated with superconductivity. Instead, the results can be understood within a picture of Fermi surface nesting assuming extremely low Fermi velocities and spin-orbital coupling.

Field dependence of magnetic correlations through the polarization flop transition in multiferroic TbMnO 3 : Evidence for a magnetic memory effect

The field-induced multiferroic transition in TbMnO3 has been studied by neutron scattering. Apart strong hysteresis, the magnetic transition associated with the flop of electronic polarization exhibits a memory effect: after a field sweep, TbMnO3 does not exhibit the same phase as that obtained by zero-field cooling. The strong changes in the magnetic excitations across the transition perfectly agree with a rotation of the cycloidal spiral plane indicating that the inverse Dzyaloshinski-Moriya coupling causes the giant magnetoelectric effect at the field-induced transition. The analysis of the zone-center magnetic excitations identifies the electromagnon of the multiferroic high-field phase.

Helimagnons in the Skyrmion Lattice of MnSi

In MnSi the application of a small magnetic field destabilizes the helimagnetic order in a narrow temperature interval just below the helimagnetic ordering temperature and stabilizes the formation of a hexagonal lattice of skyrmions, i.e., a lattice composed of a type of magnetic vortex lines. We have studied the skyrmion lattice in MnSi using a cold triple-axis spectrometer. Our data suggests that the skyrmion lattice represents a three-dimensional spin structure. The collective spin excitations of the skyrmion lattice are strongly reminiscent of the rich spectrum of helimagnon bands, recently shown to be a universal property of the helimagnetic state of MnSi in zero magnetic field.

Melting of magnetic correlations in charge-orbital ordered La 1 / 2 Sr 3 / 2 MnO 4 : Competition of ferromagnetic and antiferromagnetic states

The magnetic correlations in the charge and orbital ordered manganite

Scientific Review: PANDA: The Cold Three-Axis Spectrometer at FRM II

{\text{La}}_{1/2}{\text{Sr}}_{3/2}{\text{MnO}}_{4}

Antiferroquadrupolar Order in the Magnetic Semiconductor TmTe

have been studied by elastic and inelastic neutron scattering techniques. Out of the well-defined charge exchange (CE)-type magnetic structure with the corresponding magnons, a competition between CE-type and ferromagnetic fluctuations develops. Whereas ferromagnetic correlations are fully suppressed by the static CE-type order at low temperature, elastic and inelastic CE-type correlations disappear with the melting of the charge-orbital order at high temperature. In its charge-orbital disordered phase,

Polarized neutron scattering on the triple-axis spectrometer PANDA: First results

{\text{La}}_{1/2}{\text{Sr}}_{3/2}{\text{MnO}}_{4}