Strukturelle und magnetische Eigenschaften der Cu-Divanadate sowie verwandter, niedrigdimensionaler Verbindungen
The subject of this thesis is the preparation, the structural and magnetic properties of copper-divanadate CuxV2O5+x (x = 1, 2, 3 and 5) and K-Cu-Oxo-vanadate KCu5-xMgxV2O13 (x = 0; 1; 1,25 and 1,5). In these vanadates the magnetic Cu2+ ions (S=1/2) forms different one dimensional chains and two dimensional networks. Thus, the research was motivated by the search of new low-dimensional spin systems and the research of the influence of different Cu-topology or Cu-O-coordination on the magnetic behaviour. The Cu ions in CuV2O6 are ordered in chains. Magnetic measurements shows, that this compound could be described as quasi-one dimensional, isotropic S=1/2-Heisenberg chain with strong inter-chain coupling. In dependence on the Zn-substitution, Cu2-yZnyV2O7 crystallizes in two different phases (y < 0,15: alpha-Phase; y > 0,15: beta-Phase) This was proved through structural investigations. In both phases the Cu ions form spin chains, but the local Cu-O coordination in both phases is different. This leads to different magnetic behaviour. Similar to CuV2O6 the compounds of the beta-Phase could be described as isotropic Heisenberg chains. But, in alpha-Cu2-yZnyV2O7 Dzyaloshinsky-Moriya intra-chain interaction appears because of the asymmetric of the oxygen surrounding of the Cu ions. The DM-interaction leads to an canting of the antiferromagnetic ordered Cu spins. The Cu spins in Cu3V2O8 and Cu5V2O10 form complex two-dimensional networks. Magnetic measurements show a strong geometrically frustration of the spin systems in this compounds. An observed change of the Curie constant in Cu3V2O8 lead to the supposition, that the system forms Cu3 trimer to compensate the frustration. The Cu ions in KCu5V3O13 and KCu4MgV3O13 form ladders of Cu4-tetrahedra and/or Cu3-triangles. So, these ladders consist of frustrated Cu arrangements. Actually, a large frustration parameter f = 21 characterizes KCu5V3O13 as quasi-1D strongly frustrated system. In this compound the spin system counteracts against the strong frustration by building partial or entire compensate spin configurations. But there is no total dimerization of the system. Probably, the ground state of this system is a coexistence of a classical, antiferromagnetic and a quantummechanical, disordered state.
info:eu-repo/classification/ddc/530, Physik, Niedrigdimensionale Spinsysteme, Übergangsmetalloxide, Magnetismus, Struktur
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