Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf

We report magnetization measurements, full-potential band-structure calculations, and microscopic modeling for the spin-1/2 Heisenberg magnets A₂CuP₂O₇ (A = Na, Li) involving complex Cu-O-O-Cu superexchange pathways. Based on a quantitative evaluation of the leading exchange integrals and the subsequent quantum Monte Carlo simulations, we propose a quasi-one-dimensional magnetic model for both compounds, in contrast to earlier studies that conjectured on a two-dimensional scenario. The one-dimensional nature of A₂CuP₂O₇ is unambiguously verified by magnetization isotherms measured in fields up to 50 T. The saturation fields of about 40 T for both Li and Na compounds are in excellent agreement with the intrachain exchange J₁ is about 27 K extracted from the magnetic susceptibility data. The proposed magnetic structure entails spin chains with the dominating antiferromagnetic nearest-neighbor interaction J₁ and two inequivalent, nonfrustrated antiferromagnetic interchain couplings of about 0.01J₁ each. A possible long-range magnetic ordering is discussed in comparison with the available experimental information