Peculiar long-range superexchange in Cu2A2O7 (A = P, As, V) as a key element of the microscopic magnetic model

TL;DR

This study combines theoretical and experimental methods to analyze the magnetic interactions in Cu2A2O7 compounds, revealing how different A-site elements influence long-range superexchange mechanisms and magnetic ordering.

Contribution

It uncovers the role of AO4 side groups in governing superexchange pathways, contrasting the effects of d- and p-element A-site substitutions in Cu2A2O7 compounds.

Findings

Long-range magnetic order at T_N=27 K in alpha-Cu2P2O7.

Superexchange pathways differ based on A-site element nature.

Qualitative differences in coupling regimes explained by AO4 group chemistry.

Abstract

A microscopic magnetic model for alpha-Cu2P2O7 is evaluated in a combined theoretical and experimental study. Despite a dominant intradimer coupling J1, sizable interdimer couplings enforce long-range magnetic ordering at T_N=27 K. The spin model for alpha-Cu2P2O7 is compared to the models of the isostructural beta-Cu2V2O7 and alpha-Cu2As2O7 systems. As a surprise, coupled dimers in alpha-Cu2P2O7 and alternating chains in alpha-Cu2As2O7 contrast with a honeycomb lattice in beta-Cu2V2O7. We find that the qualitative difference in the coupling regime of these isostructural compounds is governed by the nature of AO4 side groups: d-elements (A = V) hybridize with nearby O atoms forming a Cu-O-A-O-Cu superexchange path, while for p-elements (A = P, As) the superexchange is realized via O-O edges of the tetrahedron. Implications for a broad range of systems are discussed.