The Schwinger-boson mean-field theory is used to study the threedimensional antiferromagnetic ordering and excitations in compounds L2BaNiO5, a large family of quasi-one-dimensional mixed-spin antiferromagnet. To investigate magnetic properties of these compounds, we introduce a three-dimensional mixed-spin antiferromagnetic Heisenberg model based on experimental results for the crystal structure of L2BaNiO5. This model can explain the experimental discovery of coexistence of Haldane gap and antiferromagnetic long-range order below Néel temperature. Properties such as the low-lying excitations, magnetizations of Ni and rare-earth ions, Néel temperatures of different compounds, and the behavior of Haldane gap below the Néel temperature are investigated within this model, and the results are in good agreement with neutron scattering experiments. PACS numbers: 75.10.Jm,75.50.Ee,75.50.-y Typeset using REVTEX 1 I
To submit an update or takedown request for this paper, please submit an Update/Correction/Removal Request.