Fu Hua-Hua, Yao Kai-Lun, Liu Zu-Li
Department of Physics, Huazhong University of Science and Technology, Wuhan 430074, People's Republic of China.
J Chem Phys. 2008 Oct 7;129(13):134706. doi: 10.1063/1.2987719.
Magnetic properties of two very-high-spin organic pi-conjugated polymers have been investigated theoretically by means of the many-body Green's function method with random phase approximation. The polymers are designed with a large density of cross-links and alternating connectivity of radical modules with unequal spin quantum numbers (S), macrocyclic S=2 or 3, and cross-linking S=1/2 modules, which permit large net S values for either antiferromagnetic or ferromagnetic exchange coupling between the modules. The numerical results reveal that, ascribing to the zero-temperature spin fluctuations, the sublattice magnetizations of the two polymers are both smaller than their classical spin values and the ground-state magnetizations of them are also smaller than their predicted values in the antiferromagnetic exchange coupling case. However, these magnetic behaviors do not occur in the ferromagnetic exchange coupling case. On the basis of our synthesis of the temperature dependence of the magnetic susceptibility multiplied by temperature, and through comparing the theoretical results with the experimental measurements, it is concluded that the magnetic exchange couplings between the modules within the two high-spin polymers should be ferromagnetic exchange couplings, which are consistent with other theoretical results drawn from the investigations into the ground-state properties of the two organic polymers.
利用具有随机相位近似的多体格林函数方法，对两种超高自旋有机π共轭聚合物的磁性进行了理论研究。这些聚合物设计有高密度的交联结构，以及具有不等自旋量子数（S）的自由基模块的交替连接性，大环S = 2或3，以及交联S = 1/2模块，这使得模块之间的反铁磁或铁磁交换耦合能够实现较大的净S值。数值结果表明，由于零温自旋涨落，两种聚合物的亚晶格磁化强度均小于其经典自旋值，并且它们的基态磁化强度也小于反铁磁交换耦合情况下的预测值。然而，这些磁性行为在铁磁交换耦合情况下并未出现。基于我们对磁化率乘以温度的温度依赖性的综合研究，并通过将理论结果与实验测量结果进行比较，得出结论：两种高自旋聚合物内模块之间的磁交换耦合应为铁磁交换耦合，这与从对这两种有机聚合物基态性质的研究中得出的其他理论结果一致。
