Bo Gu¹, Gang Su^1,3 and Song Gao²

¹ College of Physical Sciences, Graduate University of Chinese Academy of Sciences, PO Box 4588, Beijing 100049, People’s Republic of China

² College of Chemistry and Molecular Engineering, State Key Laboratory of Rare Earth Materials Chemistry and Applications, Peking University, Beijing 100871, People’s Republic of China

E-mail: gsu@gucas.ac.cn

Received 17 May 2005, in final form 22 August 2005

Published 9 September 2005

Online at stacks.iop.org/JPhysCM/17/6081

Abstract

    By means of the density matrix renormalization group (DMRG) method, the magnetic properties of the J–J–J ' quantum Heisenberg chains with spin S = 1/2, 1, 3/2 and 2 in the ground states are investigated in the presence of a magnetic field. Two different cases are considered. (a) When J is antiferromagnetic and J ' is ferromagnetic (i.e. the AF–AF–F chain), the system is a ferrimagnet. The plateaus of the magnetization are observed. It is found that the width of the plateaus decreases with increasing ferromagnetic coupling, and disappears when J ' /J passes a critical value. The saturated field is observed to be independent of the ferromagnetic coupling. (b) When J is ferromagnetic and J ' is antiferromagnetic (i.e. the F–F–AF chain), the system becomes an antiferromagnet. The plateaus of the magnetization are also seen. The width of the plateaus decreases with decreasing antiferromagnetic coupling, and disappears when J ' /J passes a critical value. Though the ground state properties are quite different, the magnetization plateaus in both cases tend to disappear when the ferromagnetic coupling becomes more dominant. Besides, no fundamental difference between the systems with spin half-integer and integer has been found.

(Some figures in this article are in colour only in the electronic version)