Magnetization process of the S=1 ferromagnetic–antiferromagnetic alternating Heisenberg chain

Abstract

We study the magnetic properties of the S=1 ferromagnetic–antiferromagnetic bond-alternating Heisenberg chain with single-ion-type anisotropy at zero temperature. We obtain the magnetization curve of this system using a recently developed numerical renormalization group method. We find that there is a plateau at the half-magnetized state in the high-field magnetization process, which is similar to that in the antiferromagnetic–antiferromagnetic alternating chain. In addition, the present system undergoes a first-order transition in the magnetization process which is a new magnetic property of quantum Heisenberg magnets in one dimension. We estimate the values of transition fields and the length of the plateau as a function of alternation ratio to obtain the ground-state phase diagram. We also discuss the effects of the anisotropy.