148 research outputs found
Temperature dependence of single particle excitations in a S=1 chain: Exact diagonalization calculations compared to neutron scattering experiments
No full textExact diagonalization calculations of finite antiferromagnetic spin-1 Heisenberg chains at finite temperatures are presented and compared to a recent inelastic neutron scattering experiment for temperatures T up to 7.5 times the intrachain exchange constant J. The calculations show that the excitations at the antiferromagnetic point q=1 and at q=0.5 remain resonant up to at least T=2J, confirming the recent experimental observation of resonant high-temperature domain wall excitations. The predicted first and second moments are in good agreement with experiment, except at temperatures where three-dimensional spin correlations are most important. The ratio of the structure factors at q=1 and 0.5 is well predicted for the paramagnetic infinite-temperature limit. For T<2J, however, we found that the experimentally observed intensity is considerably less than predicted. This suggests that domain wall excitations on different chains interact up to temperatures of the order of the spin band width
Neutron Science Roadmap for Research Infrastructures 2025–2028 by the Swiss Neutron Science Community
No full textThis community roadmap presents a broad overview of the current status of neutron science in Switzerland and derives a set of recommendations for future developments. It is the result of a community effort led by the Swiss Neutron Science Society (SNSS) with the main objectives to survey and analyse the unique contributions that neutron probes provide across scientific and technological fields and disciplines; and provisions needed to ensure continuing and sustainable success. The roadmap represents the view of the Swiss scientific community in the field of neutron science and is a formal element of the process to elaborate the Swiss Roadmap for Research Infrastructures 2023. This bottom-up contribution to the identification and selection of important national and international research infrastructures has been coordinated by the Swiss Academy of Sciences (SCNAT) on a mandate by the State Secretariat for Education, Research and Innovation (SERI).Rønnow HM, Gasser U, Krämer K, Strobl M, Kenzelmann M (2021) Neutron Science Roadmap for Research Infrastructures 2025–2028 by the Swiss Neutron Science Community. Swiss Academies Reports 16 (7
Substantially enhanced cloning efficiency of SAGE (Serial Analysis of Gene Expression) by adding a heating step to the original protocol
No full textComment on Ferroelectricity in Spiral Magnets
No full textA Comment on the Letter by Maxim Mostovoy, [Phys. Rev. Lett. 96, 067601 (2006)]. The author of the Letter offers a Reply
Comment on "Ferroelectricity in Spiral Magnets'' - Mostovoy replies
No full textA Reply to the Comment by M. Kenzelmann and A. B. Harris. Received 4 December 2006 DOI:https://doi.org/10.1103/PhysRevLett.100.089702 ©2008 American Physical Societ
Feliciter Pium qvod Illustri Ac Generosissimo Domino Domino Gotthelff Friedrich à Schönberg, Domino in Bieberstein, Lockwitz, & Trebiz, Potentissimi Regis Poloniarum & Electoris Sax. in Senatu intimiori Consiliario, inq[ue] Judicio Appellationum Præsidi Excellentissimo, Redituum Provincialium hactenus, & jam tum Sanctioris Senatus Directori ac Præsidi eminentissimo Domino meo Gratiosissimo cùm Purpuram eminentissimi officii ad mandatum Regiæ Majestatis in Proto-Synedrio iudueret Ecclesiis per Saxoniam Misniamqve œcumenice plaudentibus Kenzelmannorum Trebicensium & suo nomine Pridie Iduum Febr. M DCC IV. ... acclamare voluit ... M. Gottfried Kenzelmann, Burckartsdorffensium Pastor.
No full textGlückwunsch auf Gotthelf Friedrich von Schönberg zur Amtseinführung, Febr. 1704Vorlageform des Erscheinungsvermerks: Neo-Ostræ, Stanno Schwenckiano
Neutron scattering studies of three one-dimensional antiferromagnets
No full textLow-dimensional magnets with low-spin quantum numbers are ideal model systems for investigating strongly interacting macroscopic quantum ground states and their non-linear spin excitations. This thesis describes neutron scattering experiments of three one-dimensional low-spin antiferromagnets where strong quantum fluctuations lead to highly-correlated ground states and unconventional cooperative spin excitations. The excitation spectrum of the antiferromagnetic spin-1 Heisenberg chain CsNiCI_3 was investigated for a wide range of temperatures and wave-vectors. The well-defined excitations survive as a resonance to much higher temperatures than previously thought. These high-temperature resonant excitations may be regarded as high-temperature domains walls of the remainder of a zero-temperature hidden spin order. The low-temperature phase contains multi-particle states which are not predicted by theory and which resemble the two-spinon states observed in spin-1/2 chains. The excitations in the ordered phase of the antiferromagnetic spin-1/2 Heisenberg chain BaCu_2Si_2O_7 were investigated using inelastic neutron scattering. The dispersion of spin-waves, which dominate the low-frequency spectrum, was measured in three different directions perpendicular to the chain and the interchain exchange interactions were determined. A continuum of states sets in above a well-defined threshold frequency and becomes indistinguishable from the multi-particle states observed in the disordered phase of spin-1/2 chains. The magnetic order of the one-dimensional spin-1/2 XY antiferromagnet Cs_2CoCl_4 was investigated using neutron diffraction. The magnetic structure has an ordering wave-vector (0, 0.5, 0.5) for T < 217 mK and the magnetic structure is a non-linear structure with the magnetic moments at a small angle to the b axis. Above a field of H = 2.1 T the magnetic order collapses in an apparent first order phase transition, suggesting a transition to a spin-liquid phase. (author)Available from British Library Document Supply Centre-DSC:D216746 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo
Feliciter Pium qvod Illustri Ac Generosissimo Domino Domino Gotthelff Friedrich à Schönberg, Domino in Bieberstein, Lockwitz, & Trebiz, Potentissimi Regis Poloniarum & Electoris Sax. in Senatu intimiori Consiliario, inq[ue] Judicio Appellationum Præsidi Excellentissimo, Redituum Provincialium hactenus, & jam tum Sanctioris Senatus Directori ac Præsidi eminentissimo Domino meo Gratiosissimo cùm Purpuram eminentissimi officii ad mandatum Regiæ Majestatis in Proto-Synedrio iudueret Ecclesiis per Saxoniam Misniamqve œcumenice plaudentibus Kenzelmannorum Trebicensium & suo nomine Pridie Iduum Febr. M DCC IV. ... acclamare voluit ... M. Gottfried Kenzelmann, Burckartsdorffensium Pastor.
No full textGlückwunsch auf Gotthelf Friedrich von Schönberg zur Amtseinführung, Febr. 1704Vorlageform des Erscheinungsvermerks: Neo-Ostræ, Stanno Schwenckiano
Ferroelectric control of magnetism in artificial multiferroic composites
No full textIn this thesis, we studied ferromagnet/ferroelectric heterostructures, so-called artificial multiferroic composites, which exhibit magnetoelectric coupling between different ferroic order parameters. For a range of material combinations, we found that electrical switching of the ferroelectric polarization induces non-volatile reversible magnetization changes in the magnetic constituent and we contributed to the understanding of the underlying interface coupling mechanisms.
The ferromagnet/ferroelectric system La_{0.7}Sr_{0.3}MnO_{3}/ [Pb(Mg_{1/3}Nb_{2/3})O_{3}]_{0.68}-[PbTiO_{3}]_{0.32} (011) (LSMO/PMN-PT) enables magnetoelectric control of the double exchange interaction via strain. Reversible electrical switching of the ferroelectric polarization induces a 10 K shift of the magnetic Curie temperature Tc. A similar magnitude in Tc change has been previously only observed under applied electric fields. Sweeping between oppositely out of plane (OOP) poled ferroelectric polarization directions, PMN-PT (011) may exhibit an in-plane (IP) poled state where the ferroelectric polarization lies in the surface plane. OOP and IP poled configurations are stable at remanence and reciprocal space maps highlight the accompanying lattice parameter changes which impose a biaxial strain on the manganite thin film. The magnetic response to the strain changes is probed by temperature dependent Mn L_{3,2} x-ray magnetic circular dichroism (XMCD) providing quantitative values of the Mn spin and orbital moment. X-ray natural linear dichroism spectra for both strain states probe changes in the valence charge anisotropy. Multiplet and density functional theory calculations support the picture that the existing population imbalance between out of plane and in plane oriented orbitals increases further with tensile strain, favoring orbital occupation in the surface plane. An increase in tensile in-plane strain leads to an increased energy difference between the two e{_g} orbitals and a larger Mn-O-bond length. Increasing the electron-lattice coupling and reducing the e{_g} electron itinerancy that leads to ferromagnetism due to the double exchange interaction, results ultimately in lower Tc values in agreement with the Millis model.
In Co/PMN-PT (011), we disentangle the strain and charge contributions to the magnetic response upon electrical switching, using XMCD at the Co L_{3,2} edges as the main probe.
Our results evidence the coexistence of two coupling mechanisms leading to three distinct magnetization states upon electrical switching. If the ferroelectric polarization is switched to the IP poled state, the corresponding lattice parameter changes in the PMN-PT exert a strain on the Co layer and induce an anisotropy change with higher remanent magnetization along the [011-] direction.
When comparing oppositely OOP poled ferroelectric polarization configurations, an additional Co anisotropy change is observed. Since the structure of PMN-PT in the two OOP poled states is equivalent, this dependence of the anisotropy must stem from the substrate polarity. The bound charge at the interface is expected to be screened by the cobalt metal within the Thomas Fermi screening length of a few Angstroms. We use a Co wedge geometry to study the magnetic response as a function of Co layer thickness employing XMCD with surface sensitive total electron yield detection. Consequently, the anisotropy change induced by the charged substrate is observed for the thinner part but absent in the thicker part of the Co wedge.
Lattice parameter values for cobalt and PMN-PT obtained by x-ray diffraction as well as domain distributions obtained from atomic force microscopy serve as an input for density functional theory calculations which reproduce the experimentally observed anisotropy behaviour for fcc (111) textured cobalt as a function of the lateral strain and charge.
Our investigation unravels how magnetoelasticity and interfacial charge density trigger changes in the magnetic anisotropy. The observed coexistence of multiple coupling mechanisms opens up the possibility to tune and enhance the cross-coupling between layers in heterostructures.
The possibility to induce ferromagnetism in a per se paramagnetic system via electrical switching is explored for a Pd/Pb(Zr_{0.2}Ti_{0.8})O_{3} heterostructure.
Pd has a large magnetic susceptibility and is close to fulfilling the Stoner criterion for magnetism. According to calculations the polarity of adjacent ferroelectric layers could trigger a paramagnetic/ferromagnetic transition in paramagnetic metals by introducing shifts in the density of states.
No XMCD difference signal upon ferroelectric switching was found within the noise ratio of 0.2% at the M_{3,2} edge and of 1% at the L_{3,2} edge
Substantially enhanced cloning efficiency of SAGE (Serial Analysis of Gene Expression) by adding a heating step to the original protocol
No full textThe efficiency of the original SAGE (Serial Analysis of Gene Expression) protocol was limited by a small average size of cloned concatemers. We describe a modification of the technique that overcomes this problem. Ligation of ditags yields concatemers of various sizes. Small concatemers may aggregate and migrate with large ones during gel electrophoresis. A heating step introduced before gel electrophoresis breaks such contaminating aggregates. This modification yields cloned concatemers with an average size of 67 tags as compared to 22 tags by the original protocol. It enhances the length of cloned concatemers substantially and reduces the costs of SAG
- …
