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- ItemMagnon spectrum of the helimagnetic insulator Cu2OSeO3(London : Nature Publishing Group, 2016) Portnichenko, P.Y.; Romhányi, J.; Onykiienko, Y.A.; Henschel, A.; Schmidt, M.; Cameron, A.S.; Surmach, M.A.; Lim, J.A.; Park, J.T.; Schneidewind, A.; Abernathy, D.L.; Rosner, H.; van den Brink, Jeroen; Inosov, D.S.Complex low-temperature-ordered states in chiral magnets are typically governed by a competition between multiple magnetic interactions. The chiral-lattice multiferroic Cu2OSeO3 became the first insulating helimagnetic material in which a long-range order of topologically stable spin vortices known as skyrmions was established. Here we employ state-of-the-art inelastic neutron scattering to comprehend the full three-dimensional spin-excitation spectrum of Cu2OSeO3 over a broad range of energies. Distinct types of high- and low-energy dispersive magnon modes separated by an extensive energy gap are observed in excellent agreement with the previously suggested microscopic theory based on a model of entangled Cu4 tetrahedra. The comparison of our neutron spectroscopy data with model spin-dynamical calculations based on these theoretical proposals enables an accurate quantitative verification of the fundamental magnetic interactions in Cu2OSeO3 that are essential for understanding its abundant low-temperature magnetically ordered phases.
- ItemTwo types of magnetic shape-memory effects from twinned microstructure and magneto-structural coupling in Fe1 +yTe(Washington : National Academy of Sciences, 2019) Rößler, S.; Koz, C.; Wang, Z.; Skourski, Y.; Doerr, M.; Kasinathan, D.; Rosner, H.; Schmidt, M.; Schwarz, U.; Rößler, U.K.; Wirth, S.A detailed experimental investigation of Fe1+yTe (y = 0.11, 0.12) using pulsed magnetic fields up to 60 T confirms remarkable magnetic shape-memory (MSM) effects. These effects result from magnetoelastic transformation processes in the low-temperature antiferromagnetic state of these materials. The observation of modulated and finely twinned microstructure at the nanoscale through scanning tunneling microscopy establishes a behavior similar to that of thermoelastic martensite. We identified the observed, elegant hierarchical twinning pattern of monoclinic crystallographic domains as an ideal realization of crossing twin bands. The antiferromagnetism of the monoclinic ground state allows for a magnetic-field–induced reorientation of these twin variants by the motion of one type of twin boundaries. At sufficiently high magnetic fields, we observed a second isothermal transformation process with large hysteresis for different directions of applied field. This gives rise to a second MSM effect caused by a phase transition back to the field-polarized tetragonal lattice state.
- ItemThe suitability of infrared temperature measurements for continuous temperature monitoring in gilts(Göttingen : Copernicus, 2014) Schmidt, M.; Ammon, C.; Schön, P.C.; Manteuffel, C.; Hoffmann, G.The aim of this study was to evaluate whether an infrared thermometer, a pyrometer, could detect the body surface temperature in the orbital area of gilts without contacting them. Furthermore, it was tested whether an increase in the gilts' temperatures could be detected. Therefore, fever was induced. During 11 trials, 43 German Landrace gilts were injected with either a Porcilis AR-T DF (Intervet International B.V., Boxmeer, Netherlands) vaccine or 2 ml of 0.9 % NaCl. A commercial temperature logger (TRIX-8, LogTag Recorders, Auckland, New Zealand) was placed in the vagina to record temperature data every 3 min. The pyrometer (optris cs, Optris, Berlin, Germany) was aimed at where the orbital area of the gilts would be. While they were drinking, temperature measurements were done in that site by the pyrometer. Time periods from 0.25 to 6 h were analysed. Considering the 0.25-h period, a positive correlation (ρ=0.473) between temperatures of the logger and the pyrometer was found for 15 of 39 gilts. The longer the chosen measuring period was, the fewer animals showed a significant correlation between the two temperatures. In contrast to the vaginal logger, the pyrometer cannot detect an increase in the body temperature in all fever-induced gilts. In conclusion, a pyrometer cannot detect the body surface temperature reliably. An increase in the body surface temperature over a short time period (on average 5 h) could not be detected by the pyrometer. The temperature increase measured using the pyrometer was too low and time-delayed compared to the temperature detected by the vaginal logger.
- ItemElectronic structure and magnetic properties of the spin-1/2 Heisenberg system CuSe2O5(Milton Park : Taylor & Francis, 2009) Janson, O.; Schnelle, W.; Schmidt, M.; Prots, Yu; Drechsler, S.-L.; Filatov, S.K.; Rosner, H.A microscopic magnetic model for the spin-1/2 Heisenberg chain compound CuSe2O5 is developed based on the results of a joint experimental and theoretical study. Magnetic susceptibility and specific heat data give evidence for quasi-one-dimensional (1D) magnetism with leading antiferromagnetic (AFM) couplings and an AFM ordering temperature of 17 K. For microscopic insight, full-potential density functional theory (DFT) calculations within the local density approximation (LDA) were performed. Using the resulting band structure, a consistent set of transfer integrals for an effective one-band tight-binding model was obtained. Electronic correlations were treated on a mean-field level starting from LDA (LSDA+U method) and on a model level (Hubbard model). With excellent agreement between experiment and theory, we find that only two couplings in CuSe2O5 are relevant: the nearest-neighbour intra-chain interaction of 165 K and a non-frustrated inter-chain (IC) coupling of 20 K. From a comparison with structurally related systems (Sr2Cu(PO4)2, Bi2CuO4), general implications for a magnetic ordering in presence of IC frustration are made.