Shou-Shu Gong, Bo Gu, Gang Su^∗

College of Physical Sciences, Graduate University of Chinese Academy of Sciences, PO Box 4588, Beijing 100049, China

Received 8 November 2007; accepted 19 November 2007

Available online 28 November 2007

Communicated by V.M. Agranovich

Abstract:

     By means of the density matrix renormalization group (DMRG) method, the static spin structure factors and the magnetization plateaus of the trimerized Heisenberg ferromagnet–ferromagnet–antiferromagnet and antiferromagnet–antiferromagnet–ferromagnet spin chains in the presence of a magnetic field are elaborately studied. It is found that in the plateau states, the static structure factor with three peaks does not vary with the external magnetic field as well as the exchange couplings; the spin correlation function behaves as a perfect sequence and has a simple relation with the magnetization per site. An approximate wave function for the plateau states is proposed, and a picture based on the valence-bond-solid states is presented in order to understand the origin and the total number of the magnetization plateaus, which are shown to be in agreement with the DMRG results.