Universität zu Köln

Kunkemöller, Stefan (2018). Spin-orbit effects and competing magnetic correlations in layered Ruthenates: A neutron scattering study using floating-zone grown single crystals. PhD thesis, Universität zu Köln.

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Abstract

Once more, neutron scattering using large high-quality single crystals is proven to be a powerful technique to study magnetism on a microscopic level. Several layered Ruthenate single-crystals could be grown in better quality or larger dimensions than the existing crystals at the starting of this work, enabling the neutron scattering studies [10, 35, 25, 36, 26]. Thus important progress in the research of layered Ruthenates could be achieved: The incommensurable magnetic fluctuations in Sr2RuO4 , which are induced by the Fermi-surface nesting of the quasi one-dimensional bands, were studied in the superconducting and non-superconducting state up to very low energy transfers, far below the expected cooper-pair binding energies. Therefore, it is strongly suggested that the quasi one-dimensional bands are not the active bands driving the superconductivity, giving an important contribution to the question of the symmetry of the superconducting order parameter. The magnon dispersion of Ca2RuO4 was determined throughout the whole first Brillouin zone giving an important contribution to the discussion of the ground state of this compound and revealing the enhanced strength of spin-orbit coupling in that 4d system. The oxygen octahedron rotation of SrRuO3 was determined with high precision very efficiently. Thus, it became possible to shed light on the six-fold twinning of this compound and the changing twinning fraction induced by magnetic fields. A reorientation of the crystal structure in the magnetic phase induced by magnetic fields and a memory effect of the reorientation, which goes in hand with a magnetic shape-memory effect, was discovered in that oxide. The spin density distribution in the unit cell of SrRuO3 could be reconstructed using polarized neutron diffraction data. A spin-density wave has been confirmed in Ca0.5Sr1.5RuO4 . The propagation vector amounts to (0.305,0.305,1) and the spins freeze in like in spin- or cluster- glasses becoming static at about 4K [10].

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Kunkemöller, Stefan kunkemoeller@ph2.uni-koeln.de UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-82318
Date:	2018
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Physics > Institute of Physics II
Subjects:	Physics
Uncontrolled Keywords:	Keywords Language Ruthenates, neutron scattering, spin-orbit effects, magnetic correlations, strongly correlated electrons, superconductivity, Mott-Insulator, magnetic shape-memory effect, spin-density wave, crystal growth, floating-zone, x-ray scattering, magnetization English
Date of oral exam:	12 December 2017
Referee:	Name Academic Title Braden, Markus Prof. Dr. Grüninger, Markus Prof. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/8231