# Dresden 2006 – wissenschaftliches Programm

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# TT: Tiefe Temperaturen

## TT 19: Correlated Electrons: Low-dimensional Materials

### TT 19.7: Vortrag

### Dienstag, 28. März 2006, 15:30–15:45, HSZ 301

**Electronic structure and magnetic properties of the spin-****1/2**** system Bi**_{2}**CuO**_{4} — •Oleg Janson^{1,2} and Helge Rosner^{1} — ^{1}MPI CPfS Dresden — ^{2}SPbSU St. Petersburg, Russia

Bi_{2}CuO_{4} crystallizes in the tetragonal system, with isolated CuO_{4} plaquettes arranged parallel to the *xy* plane and staggered in chains along the *z* axis. Initially, Bi_{2}CuO_{4} was treated as 1D compound, but low temperature data, especially the magnetic moment of 0.93 µ_{B}, show that quantum fluctuations are strongly suppressed and exclude a 1D model. Neutron scattering data reveal FM-ordered chains along *z*, that are AFM ordered with respect to each other [1]. To elucidate the origin of the surprisingly FM-ordered chains, we performed DFT calculations to evaluate the relevant orbitals and couplings. Total energy calculations yield a magnetic groundstate coinciding with the experimental data. From a tight-binding fit of the LDA band structure we obtained the exchange integrals. The most important result is that the main coupling is between the chains and the in-chain interaction is relatively small. Thus, the FM arrangement of chains is due to strong AFM exchange of neighbouring plaquettes that belong to the different chains. Therefore, Bi_{2}CuO_{4} has to be described as a compound with 3D coupling.

*This investigation was supported by the DFG, Emmy Noether-program*

[1] J. L. García-Muñoz, J. Rodríguez-Carvajal et al. J. Phys.: Condens. Matter, **2** (1990) 2205–2214