Schwinger-Boson Mean-Field Theory of Mixed-Spin Antiferromagnet L2BaNiO5
Abstract
The Schwinger-boson mean-field theory is used to study the three-dimensional 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 N\'eel temperature. Properties such as the low-lying excitations, magnetizations of Ni and rare-earth ions, N\'eel temperatures of different compounds, and the behavior of Haldane gap below the N\'eel temperature are investigated within this model, and the results are in good agreement with neutron scattering experiments.
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