0000000000407119
AUTHOR
Klaus Doll
Pressure induced insulator/half-metal/metal transition in a strongly correlatedp-electron system
Mixed-valent Rb${}_{4}$O${}_{6}$ provides an exceptional prototype material for studying the interplay between local correlations (Hubbard $U$) and electron kinetic energy ($W$) in the open $sp$-electron shell. Based on a first-principles calculation we show that depending on $U/W$ ratio, when tuned by external pressure, Rb${}_{4}$O${}_{6}$ exhibits a surprising sequence of phase transitions between strongly correlated antiferromagnetic insulator, ferromagnetic insulator ($U/W\phantom{\rule{-0.16em}{0ex}}\ensuremath{\gg}\phantom{\rule{-0.16em}{0ex}}1$), moderately correlated ferromagnetic half-metal ($U/W\phantom{\rule{-0.16em}{0ex}}\ensuremath{\sim}\phantom{\rule{-0.16em}{0ex}}1$), and fin…
Challenge of magnetism in strongly correlated open-shell 2p systems.
We report on theoretical investigations of the exotic magnetism in rubidium sesquioxide ${\mathrm{Rb}}_{4}{\mathrm{O}}_{6}$, a model correlated system with an open $2p$ shell. Experimental investigations indicated that ${\mathrm{Rb}}_{4}{\mathrm{O}}_{6}$ is a magnetically frustrated insulator. The frustration is explained here by electronic structure calculations that incorporate the correlation between the oxygen $2p$ electrons and deal with the mixed-valent oxygen. This leads to a physical picture where the symmetry is reduced because one third of the oxygen in ${\mathrm{Rb}}_{4}{\mathrm{O}}_{6}$ is nonmagnetic while the remaining two thirds assemble in antiferromagnetic arrangements. A d…
Exotic magnetism in the alkali sesquioxidesRb4O6andCs4O6
Among the various alkali oxides the sesquioxides ${\text{Rb}}_{4}{\text{O}}_{6}$ and ${\text{Cs}}_{4}{\text{O}}_{6}$ are of special interest. Electronic-structure calculations using the local spin-density approximation predicted that ${\text{Rb}}_{4}{\text{O}}_{6}$ should be a half-metallic ferromagnet, which was later contradicted when an experimental investigation of the temperature-dependent magnetization of ${\text{Rb}}_{4}{\text{O}}_{6}$ showed a low-temperature magnetic transition and differences between zero-field-cooled and field-cooled measurements. Such behavior is known from spin glasses and frustrated systems. ${\text{Rb}}_{4}{\text{O}}_{6}$ and ${\text{Cs}}_{4}{\text{O}}_{6}$ c…
Synthesis and Magnetic Properties of Novel Azamacrocyclic LnIII, CuII, FeIII, and SrII Complexes and Conformational Analysis of the Ligands
Hexaalkoxy-substituted azamacrocyclic metal complexes 1 · MXn [MXn = FeCl3, CuCl2, SrCl2, Ln(NO3)3; Ln = La, Pr, Eu, Ho, Er] with various chain lengths were prepared by a convergent approach using 1,2-bisalkoxy-4,5-diamines 3 and 4-alkoxy-pyridine-2,6-dicarbaldehydes 4 as key building blocks for template-assisted cyclocondensation. Metal complexes 1 · MXn were considered as potential metallomesogens. However, differential scanning calorimetry and optical polarizing microscopy of 1 · MXn did not reveal any mesomorphism. The magnetic susceptibility shows deviation from Curie-like behavior. Due to ligand field effects the effective magnetic moments are a function of the temperature. In order t…