Eur. Phys. J. B 75, 489-495 (2010)
https://doi.org/10.1140/epjb/e2010-00168-4

Cooperative order and excitation spectra in the bicomponent spin networks

Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100080, P.R. China

Corresponding author: ^a xubao@aphy.iphy.ac.cn

Received: 2 October 2009
Revised: 6 May 2010
Published online: 4 June 2010

Abstract

A ferrimagnetic spin model composed of S = 1/2 spin-dimers and S = 5/2 spin-chains is studied by combining the bond-operator representation (for S = 1/2 spin-dimers) and Holstein-Primakoff transformation (for S = 5/2 spins). A finite interaction J_DF between the spin-dimer and the spin chain makes the spin chains ordered antiferromagnetically and the spin dimers polarized. The effective interaction between the spin chains, mediated by the spin dimers, is calculated up to the third order. The staggered magnetization in the spin dimer is shown proportional to J_DF. Due to the triplon-magnon interaction, the degeneracy of the triplons is lifted and the hybridized triplon-like excitations show different behaviors near the vanishing J_DF. A mode with longitudinal polarization is identified. The hybridized magnon-like excitations are also studied. These results are compared with the experiments on Cu₂Fe₂Ge₄O₁₃.