Collective excitations in ferrimagnetic Heisenberg ladders

Abstract

We study ground-state properties and the low-lying excitations of Heisenberg spin ladders composed of two ferrimagnetic chains with alternating site spins $(S_1>S_2)$ by using the bosonic Dyson-Maleev formalism and Lanczos numerical techniques. The emphasis is on properties of the ferrimagnetic phase which is stable for antiferromagnetic interchain couplings $J_{\perp }\ge 0$. There are two basic implications of the underlying lattice structure: (i) the spin-wave excitations form folded acoustic and optical branches in the extended Brillouin zone and (ii) the ground state parameters (such as the on-site magnetizations and spin-stiffness constant) show a crossover behavior in the weak-coupling region $0<J_{\perp }<1$. The above peculiarities of the ladder ferrimagnetic state are studied up to second order in the quasiparticle interaction and by a numerical diagonalization of ladders containing up to N=12 rungs. The presented results for the ground-state parameters and the excitation spectrum can be used in studies on the low-temperature thermodynamics of ferrimagnetic ladders.

9 pages, 9 figures

References in corpus (5)

• Coupled Ladders in a Magnetic Field
• Characterization of ferrimagnetic Heisenberg chains according to the constituent spins
• Magnon dispersions in quantum Heisenberg ferrimagnetic chains at zero temperature
• Phase diagram of ferrimagnetic ladders with bond-alternation
• Alternating-Spin Ladders in a Magnetic Field: New Magnetization Plateaux

Cited by in corpus (9)

• Bosonic representation of one-dimensional Heisenberg ferrimagnets
• Phase diagram of a frustrated mixed-spin ladder with diagonal exchange bonds
• Antiferromagnetically coupled alternating spin chains
• Phase diagram of a coupled tetrahedral Heisenberg model
• Low-energy structure of the intertwining double-chain ferrimagnets A_3_Cu_3_(PO_4_)_4_ (A=Ca,Sr,Pb)
• Ferrimagnetic mixed-spin ladders in weak and strong coupling limits
• Mixed-spin Heisenberg ladders in a magnetic field
• Magnetic phase diagram of a frustrated ferrimagnetic ladder: Relation to the one-dimensional boson Hubbard model
• Quantum fluctuation effects on the ordered Moments in a two dimensional frustrated ferrimagnet