P. Steffens

Inelastic neutron-scattering measurements of incommensurate magnetic excitations on superconducting LiFeAs single crystals.

N. Qureshi, P. Steffens, Y. Drees, A. C. Komarek, D. Lamago, 4 Y. Sidis, L. Harnagea, H.-J. Grafe, S. Wurmehl, B. Büchner, and M. Braden ∗ II. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, D-50937 Köln, Germany Institut Laue Langevin, BP156X, 38042 Grenoble Cedex, France Laboratoire Léon Brillouin, C.E.A./C.N.R.S., F-91191 Gif-sur-Yvette Cedex, France Institut für Festkörperphysik, Karlsruher Institut für Technologie (KIT), Postfach 3640, D-76121 Karlsruhe, Germany Leibniz-Institute for Solid State Research, IFW-Dresden, 01171 Dresden, Germany (Dated: April 28, 2013)

Anisotropic Spin Dynamics in the Kondo Semiconductor CeRu 2 Al 10

Spin dynamics in the new Kondo insulator compound CeRu2Al10 has been studied using unpolarized and polarized neutron scattering on single crystals. In the unconventional ordered phase forming below T0=27.3  K, two excitation branches are observed with significant intensities, the lower one of which has a gap of 4.8±0.3  meV and a pronounced dispersion up to ≈8.5  meV. Comparison with random-phase approximation magnon calculations assuming crystal-field and anisotropic exchange couplings captures major aspects of the data, but leaves unexplained discrepancies, pointing to a key role of direction-specific hybridization between 4f and conduction band states in this compound.

Splitting of resonance excitations in nearly optimally doped Ba(Fe0.94Co0.06)2As2: an inelastic neutron scattering study with polarization analysis.

Magnetic excitations in Ba(Fe0.94Co0.06)2As2: are studied by polarized inelastic neutron scattering above and below the superconducting transition. In the superconducting state, we find clear evidence for two resonancelike excitations. At a higher energy of about 8 meV, there is an isotropic resonance mode with weak dispersion along the c direction. In addition, we find a lower excitation at 4 meV that appears only in the c-polarized channel and whose intensity strongly varies with the l component of the scattering vector. These resonance excitations behave remarkably similar to the gap modes in the antiferromagnetic phase of the parent compound BaFe2As2.

Local magnetic anisotropy in BaFe2As2: A polarized inelastic neutron scattering study

The anisotropy of the magnetic excitations in BaFe

Fine structure of the incommensurate antiferromagnetic fluctuations in single-crystalline LiFeAs studied by inelastic neutron scattering

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Magnetic excitations in the metallic single-layer ruthenates Ca2−xSrxRuO4studied by inelastic neutron scattering

As

Universality of the dispersive spin-resonance mode in superconducting BaFe2As2.

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Anisotropy of incommensurate magnetic excitations in slightly overdoped

was studied by polarized inelastic neutron scattering which allows one to separate the components of the magnetic response. Despite the in-plane orientation of the static ordered moment we find the in-plane polarized magnons to exhibit a larger gap than the out-of-plane polarized ones indicating very strong single-ion anisotropy within the layers. It costs more energy to rotate a spin within the orthorhombic {\it a-b} plane than rotating it perpendicular to the FeAs layers.

{\mathrm{Ba}}_{0.5}{\mathrm{K}}_{0.5}{\mathrm{Fe}}_{2}{\mathrm{As}}_{2}

We present an inelastic neutron scattering study on single-crystalline LiFeAs devoted to the characterization of the incommensurate antiferromagnetic fluctuations at Q = (0.5 ± �,0.5 ∓ �,ql). Time-of-flight measurements show the presence of these magnetic fluctuations up to an energy transfer of 60 meV, while polarized neutrons in combination with longitudinal polarization analysis on a triple-axis spectrometer prove the pure magnetic origin of this signal. The normalization of the magnetic scattering to an absolute scale yields that magnetic fluctuations in LiFeAs are by a factor eight weaker than the resonance signal in nearly optimally Co-doped BaFe2As2, although a factor two is recovered due to the split peaks owing to the incommensurability. The longitudinal polarization analysis indicates weak spin space anisotropy with slightly stronger out-of-plane component between 6 and 12 meV. Furthermore, our data suggest a fine structure of the magnetic signal most likely arising from superposing nesting vectors.

probed by polarized inelastic neutron scattering experiments

By inelastic neutron scattering, we have analyzed the magnetic correlations in the paramagnetic metallic region of the series Ca(2-x)Sr(x)RuO(4), 0.2<=x<=0.62. We find different contributions that correspond to 2D ferromagnetic fluctuations and to fluctuations at incommensurate wave vectors (0.11,0,0), (0.26,0,0) and (0.3,0.3,0). These components constitute the measured response as function of the Sr-concentration x, of the magnetic field and of the temperature. A generic model is applicable to metallic Ca(2-x)Sr(x)RuO(4) close to the Mott transition, in spite of their strongly varying physical properties. The amplitude, characteristic energy and width of the incommensurate components vary only little as function of x, but the ferromagnetic component depends sensitively on concentration, temperature and magnetic field. While ferromagnetic fluctuations are very strong in Ca1.38Sr0.62RuO4 with a low characteristic energy of 0.2 meV at T=1.5 K, they are strongly suppressed in Ca1.8Sr0.2RuO4, but reappear upon the application of a magnetic field and form a magnon mode above the metamagnetic transition. The inelastic neutron scattering results document how the competition between ferromagnetic and incommensurate antiferromagnetic instabilities governs the physics of this system.