Eur. Phys. J. B 75, 531-541 (2010)
https://doi.org/10.1140/epjb/e2010-00146-x

Lattice distortions in a sawtooth chain with Heisenberg and Ising bonds

¹ INFN-Laboratori Nazionali di Frascati, Via E. Fermi 40, 00044 Frascati, Italy
² Yerevan State University, A. Manoogian, 1, 0025 Yerevan, Armenia
³ Yerevan Physics Institute, Alikhanian Br.2, 0036 Yerevan, Armenia

Corresponding author: ^a ohanyan@yerphi.am

Received: 28 December 2009
Revised: 22 March 2010
Published online: 12 May 2010

Abstract

An exactly solvable model of the sawtooth chain with Ising and Heisenberg bonds and with coupling to lattice distortion for Heisenberg bonds is considered in the magnetic field. Using the direct transfer-matrix formalism an exact description of the thermodynamic functions is obtained. The ground state phase diagrams for all regions of parameters values containing phases corresponding to the magnetization plateaus at M = 0,1/4 and 1/2 have been obtained. Exact formulas for bond distortions for various ground states are presented. A mechanism of magnetization plateau stabilization with doubling of unit cell is reported. This mechanism is related with the inequivalence of right and left interaction bonds for certain lattice sites.