für Naturforschung in cooperation with the Max Planck Society for the Advancement of Science under a Creative Commons Attribution 4.0 International License. Dieses Werk wurde im Jahr 2013 vom Verlag Zeitschrift für Naturforschung in Zusammenarbeit mit der Max-Planck-Gesellschaft zur Förderung der Wissenschaften e.V. digitalisiert und unter folgender Lizenz veröffentlicht: Creative Commons Namen...

3 Kinetic exchange 7 3.1 A toy model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.2 Direct exchange . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 3.3 Second quantization for pedestrians . . . . . . . . . . . . . . . . . . . . . . . 10 3.4 Mean-field treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 3.5 Superexchange...

The effect of Gd doping and O deficiency on the electronic structure, exchange interaction, and Curie temperature of EuO in the cubic and tetragonal phases is studied by means of density functional theory. For both defects, the Curie temperature is found to exhibit a distinct maximum as a function of the defect concentration. The existence of optimal defect concentrations is explained by the in...

The synthesis, structural, electronic and magnetic characterization of five dinuclear Co(II) azacryptand compounds (1-5) bridged through different ions are reported. The magnetic exchange interactions, 2J values, obtained from theoretical computations show that the variation of the intermetallic angles and distances lead to antiferromagnetic behaviours. Magneto-structural correlations show a tr...

We investigate the influence of electron-phonon coupling on the superex-change interaction of magnetic insulators. Both the Holstein-Hubbard model where the phonons couple to the electron density, as well as an extended Su, Schrieffer, Heeger model where the coupling arises from modulation of the overlap integral are studied using exact diagonalization and perturba-tive methods. In all cases fo...

Using a hybrid method based on fermionic diagonalization and classical Monte Carlo techniques, we investigate the interplay between itinerant and localized spins, with competing double- and superexchange interactions, on a honeycomb lattice. For moderate superexchange, a geometrically frustrated triangular lattice of hexagons forms spontaneously. For slightly larger superexchange a dimerized gr...