Fe2Cu2 聚合支链中的量子磁性：来自精确求解的 Ising-Heisenberg 模型的洞见
Quantum Magnetism in Fe2Cu2 Polymeric Branched Chains: Insights from Exactly Solved Ising-Heisenberg Model
AI总结：
本文用转移矩阵法精确求解受 Fe2Cu2 配位聚合物启发的自旋 1/2 Ising-Heisenberg 支链，揭示其基态相、磁化平台与纠缠行为，并解释实验磁耦合参数。
摘要：
受三种同构聚合配位化合物 [(Tp)2Fe2(CN)6X(bdmap)Cu2(H2O)].H2O（以下记为 Fe2Cu2；Tp = 三(吡唑基)氢硼酸根，bdmapH = 1,3-双(二甲氨基)-2-丙醇，HX = 乙酸、丙酸或三氟乙酸）的磁结构启发，本文采用转移矩阵方法严格研究了自旋 1/2 Ising-Heisenberg 支链。整体基态相图揭示了三个不同的相：量子反铁磁相、量子亚铁磁相和经典铁磁相。在零温磁化曲线中，两个量子基态表现为位于零和饱和磁化强度一半处的中间平台，而磁化强度在经典铁磁相内达到其饱和值。由于 Ising 自旋的完全极化性质，最近邻 Heisenberg 自旋之间的二体纠缠在量子亚铁磁相中比在量子反铁磁相中更为显著。自旋 1/2 Ising-Heisenberg 支链的理论预测与实验测得的磁化率温度依赖关系及低温磁化曲线之间合理吻合，表明聚合化合物 Fe2Cu2 中最近邻 CuII-CuII 磁性离子之间存在强反铁磁耦合，而最近邻 CuII-FeIII 磁性离子之间存在中等强度的铁磁耦合。最近邻 CuII-CuII 磁性离子之间的热纠缠可持续到相对较高的阈值温度 T = 224 K，并经历由磁场驱动的瞬时增强。
英文摘要：
The spin-1/2 Ising-Heisenberg branched chain, inspired by the magnetic structure of three isostructural polymeric coordination compounds [(Tp)2Fe2(CN)6X(bdmap)Cu2(H2O)].H2O to be further denoted as Fe2Cu2 (Tp = tris(pyrazolyl)hydroborate, bdmapH = 1,3-bis(dimethylamino)-2-propanol, HX = acetic acid, propionic acid or trifluoroacetic acid), is rigorously studied using the transfer-matrix method. The overall ground-state phase diagram reveals three distinct phases: a quantum antiferromagnetic phase, a quantum ferrimagnetic phase and a classical ferromagnetic phase. In the zero-temperature magnetization curve, two quantum ground states are manifested as intermediate plateaus at zero and half of the saturation magnetization, while the magnetization reaches its saturated value within the classical ferromagnetic phase. The bipartite entanglement between nearest-neighbor Heisenberg spins is more pronounced in the quantum ferrimagnetic phase compared to the quantum antiferromagnetic phase due to a fully polarized nature of the Ising spins. A reasonable agreement between theoretical predictions for the spin-1/2 Ising-Heisenberg branched chain and experimental data measured for a temperature dependence of the magnetic susceptibility and a low-temperature magnetization curve suggests strong antiferromagnetic coupling between nearest-neighbor CuII-CuII magnetic ions and moderately strong ferromagnetic coupling between nearest-neighbor CuII-FeIII magnetic ions in the polymeric compounds Fe2Cu2. A thermal entanglement between nearest-neighbor CuII-CuII magnetic ions persists up to a relatively high threshold temperature T = 224 K and undergoes a transient magnetic-field-driven strengthening.
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