Magnetic excitations from an S=1/2 diamond-shaped tetramer compound Cu2PO4OH

TL;DR

This study investigates magnetic excitations in Cu2PO4OH, revealing complex interactions in S=1/2 diamond-shaped tetramers through neutron scattering, highlighting the importance of diagonal and intertetramer interactions.

Contribution

It demonstrates that simple models are insufficient and identifies the significance of diagonal and intertetramer interactions in the magnetic behavior of Cu2PO4OH.

Findings

Observed two nearly dispersionless magnetic excitations at 12 and 20 meV.

Simple square tetramer model does not fit experimental data.

Structural distortion below 160 K causes inequivalent main interactions.

Abstract

Inelastic neutron scattering experiments have been carried out on a powder sample of Cu2PO4OH, which consists of diamond-shaped tetramer spin units with S=1/2. We have observed two nearly dispersionless magnetic excitations at E1~12 and E2~20 meV, whose energy width are broader than the instrumental resolution. The simplest square tetramer model with one dominant interaction, which predicts two sharp excitation peaks at E1 and E2(=2E1), does not explain the experimental result. We found that two diagonal intratetramer interactions compete with the main interaction and weak intertetramer interactions connect the tetramers. The main intratetramer interaction is found to split into two inequivalent ones due to a structural distortion below 160 K. Cu2PO4OH is considered to be a good material to study the S=1/2 Heisenberg tetramer system.