Valence bond state in the delafossiteYCuO2.5

Abstract

We take advantage of the precise determination of the crystallographic structure ofcomplex magnetic systems with localized moments to calculate their exchange interactionvalues using ab initio methods. The magnetic interactions are mapped onto a Heisenbergmodel whose exchange interaction terms are fitted to first-principles total energycalculations for different spin configurations. This method is well adapted to systems withwell defined local moments, as is often the case in oxides. We discuss the delafossiteYCuO2.5, with triangular layers of magnetic ions without magnetic ordering, and for which themagnetic interactions are unknown. Using these ab initio parameters, we perform exactdiagonalization, which yields a valence bond solid ground state and shows excellent agreementwith experimental magnetic susceptibility, provided that the different interactions betweenCu1 and Cu2 atoms in the same triangle are taken into account.