Critical Behavior of Anisotropic Heisenberg Mixed-Spin Chains in a Field

Abstract

We numerically investigate the critical behavior of the spin-(1,1/2) Heisenberg ferrimagnet with anisotropic exchange coupling in a magnetic field. A quantized magnetization plateau as a function of the field, appearing at a third of the saturated magnetization, is stable over whole the antiferromagnetic coupling region. The plateau vanishes in the ferromagnetic coupling region via the Kosterlitz-Thouless transition. Comparing the quantum and classical magnetization curves, we elucidate what are essential quantum effects.

5 pages, Revtex, with 7 eps figures, to appear in Phys. Rev. B (An extra ps figure (fig7.ps) is included for printing.)