双向亚铁磁棱型自旋链的热力学性质研究

Thermodynamic Properties of a Ferrimagnetic Bipartite Lozenge Chain by Green's Function Method

基于近些年来试验上有机和无机磁性高分子化合物的合成,文章利用双时格林函数方法, 对AB2型双向聚合物棱型自旋链的磁学和热力学性质进行了研究．在半满强耦合极限条件下,该系统可转化为量子铁磁-反铁磁自旋为1／2的AB2型海森堡模型,该模型将由零温量子相转变到亚铁磁基态．在Tyablikov耦合近似条件下,基态的自旋波、以及亚晶格的磁化强度和系统的磁化率在不同的序参量和不同外场的条件下进行了研究．结果显示该模型低温下的性质和自旋为1／2的铁磁相互作用的海森堡链相同．

We study theoretically the thermodynamic properties of the AB2 polymeric bipartite chains with experimental motivation in inorganic and organic compounds by the double-time Green＇s function method. In the half-filled strong-coupling limit, the system can be mapped onto a quantum antiferromagnetic-ferromagentic spin-1/2 AB2 Heisenberg model, which presents a zero-temperature quantum phase transition to a ferrimagnetic ground state. Within Tyablikov＇s decoupling approximation and taking into account the quantum nature of Heisenberg model, the spin-wave spectra of the ground state is derived. Meanwhile, the sublattice magnetization and the susceptibility for different order parameters are investigated in the presence of the external magnetic fields, which indicate that their low-temperature behavior is the same as that of a quantum ferromagnetic spin-1/2 Heisenberg chain.