基于有机分子亚铁磁体棱型自旋链外场下的热力学性质研究

基于近来有机高分子亚铁磁体在试验上成功的合成，本文采用量子转移矩阵方法，研究一维反铁磁-铁磁自旋1／2棱型自旋链在外场条件下低温下的热力学性质．磁化强度在低温下随外场的变化出现台阶式的平台结构，并表现出三个临界外场值，反映了系统磁相互耦合作用与热力学波动间的相互竞争；同时磁化率在外场下呈现双峰结构，其来源于系统在外场下的能隙和长程序参量的变化．本文的数值结果表明该棱型链与自旋1-1／2海森堡链性质一致．

Thermodynamic properties of molecule-based ferrimagnetic spin chain in the external magnetic field

Motivated by recent experimental synthesis of molecule-based ferrimagnetics, we have investigated the thermodynamic properties of one-dimensional antiferromagnet ic - ferromagnetic mixed chain in external magnetic field at low temperatures using the Transfer Matrix method. The magnetization and the specific heat of the spin system have been evaluated numerically from the free energy. The magnetization as a function of the magnetic field at low temperature shows step-like plateau characterized by three critical magnetic fields, which reflects the competing effect of magnetic interactions and thermal fluctuations. The double-peak structure in the specific heat is also found, which comes from the huge variation of the long-rang order parameters. Our results are consistent with these of the Transfer Matrix renormalization group method and the exact diagonalization method.