Abstract
The Schwinger-boson mean-field theory is applied to the quantum ferrimagnetic Heisenberg chain. There is a ferrimagnetic long-range order in the ground state. We observe two branches of the low-lying excitation and calculate the spin reduction, the gap of the antiferromagnetic branch, and the spin fluctuation at These results agree with the established numerical results quite well. At finite temperatures, the long-range order is destroyed because of the disappearance of the Bose condensation. The thermodynamic observables, such as the free energy, magnetic susceptibility, specific heat, and the spin correlation at are calculated. The has a minimum at intermediate temperatures and the spin-correlation length behaves as at low temperatures. These qualitatively agree with the numerical results and the difference is small at low temperatures.
- Received 16 November 1998
DOI:https://doi.org/10.1103/PhysRevB.60.1057
©1999 American Physical Society