Schwinger-boson Mean-field Theory In The Heisenberg Spin Chain

Low-dimension magnetic system has attracted many researchers and scientistes since 1980s. Especially, Haldane presumption was published on the paper. Many researchers had tesrified the assumption by theoretical and experimental methods. From theoretical aspect, Brehmer had researched the excited states and thermodynamic properties of antiferromagnetic spin chain by spin wave theory and monte carlo method. Yamamoto also researched the thermodynamic properties of ferrimagnetic spin chain by modified spin wave theory and density-matrix renormalization-group method. C. Wu used the schwinger-boson mean-field theory to research the groud states and thermodynamic properties of ferrimagnetic spin chain. Moreover, other researchers also has researched the physical pattern of Heisenberg spin chain.In this paper, we used schwinger-boson mean-field theory to research one-dimensional ferromagnetic, antimagnetic and ferrimagnetic spin chain. In the text, we respectively discussed the quantized XXZ model, the ferrimagnetic spin chain, the anisotropic ferrimagnetic spin chain, the anisotropic ferrimagnetic spin chain in the external magnetic field and the anisotropic ferrimagnetic spin chain with next nearest neighbor interaction. In the chapter 4, we give the excited spectrum and thermodynamic properties of anisotropic ferrimagnetic spin chain, such as the energy gaps, free energy, susceptibility, specific heat. From these figures, the relationship between the thermodynamic properties and anisotropy D is clearly shown. In this paper, we mainly discuss the effect of external magnetic field, anisotropy and next nearest neighbor interaction on the one-dimensional heisenberg spin chain.