Molecular nanomagnets
Molecular nanomagnets
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DOI：
10.1080/10587250210781
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发表时间：
2002-01-01
影响因子：
0.7
通讯作者：
Aromi, G
中科院分区：
文献类型：
--
作者：
Hendrickson, DN;Christou, G;Aromi, G
我们通过几个单分子磁体 (SMM) 的例子讨论了磁化方向的量子机械隧道效应。描述了两种晶体学不同形式的 [Mn12O12(O2CC6H4-p-Me)(16)(H2O)(4)] 的磁化隧道效应。溶剂化物。这两种 Mn-12 配合物是异构体。两种异构 Mn-12 配合物的磁化强度与磁场磁滞回线有很大不同。一种 Mn-12 配合物表现出磁滞回线，其特征是比另一种 Mn-12 异构体的磁化隧道速度要快得多。一种异构体中 Jahn-Teller 伸长轴的不寻常方向导致更大的菱形零场分裂，这是更快磁化隧道的起源。除了 Mn-12 配合物的数据外，还报告了三种混合价 Mn-4 配合物的磁化弛豫速率与温度响应的关系。在所有三种情况下，磁化弛豫率对数与绝对温度倒数的阿伦尼乌斯图显示了与温度无关的区域以及与温度相关的区域。与温度无关的弛豫率是基态最低能量零场分量中磁化隧道效应的明确证据。
Quantum mechanical tunneling of the direction of magnetization is discussed for several examples of single-molecule magnets (SMM's). Magnetization tunneling is described for two crystallographically different forms of [Mn12O12(O2CC6H4-p-Me)(16)(H2O)(4)] . solvate. The two Mn-12 complexes are isomers. The magnetization versus magnetic field hysteresis loops are quite different for the two isomeric Mn-12 complexes. One Mn-12 Complex exhibits a magnetization hysteresis loop that is characteristic of considerably faster magnetization tunneling than in the other Mn-12 isomer. The unusual orientation of Jahn-Teller elongation axes in one isomer leads to greater rhombic zero-field splitting that is the origin of the faster magnetization tunneling. In addition to data for Mn-12 complexes, magnetization relaxation rate versus temperature responses of three mixed-valence Mn-4 complexes are also reported. In all three cases the Arrhenius plot of the logarithm of the magnetization relaxation rate versus the inverse absolute temperature shows a temperature-independent region as well as a temperature-dependent region. The temperature-independent relaxation rate is definitive evidence of magnetization tunneling in the lowest-energy zero-field component of the ground state.