Magneto-structural correlation in the Jahn–Teller isomers of Mn12
Magneto-structural correlation in the Jahn–Teller isomers of Mn12
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DOI：
10.1039/b604224d
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发表时间：
2006-06
影响因子：
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通讯作者：
K. Awaga;Yoshihito Suzuki;H. Hachisuka;K. Takeda
中科院分区：
文献类型：
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作者：
K. Awaga;Yoshihito Suzuki;H. Hachisuka;K. Takeda
在这篇专题文章中，我们讨论了我们在单分子磁体[Mn12O12(RCO2)16(H2O)4](简称Mn12R)中的Jahn-Teller异构体的工作，以及它们之间的磁结构相关性。在交流磁化率虚分量的温度依赖关系中，Mn12R的导数在5K和2K总是出现两个峰，这表明存在一个较慢的驰豫(SR)过程和一个较快的驰豫(FR)过程。虽然在2K处的峰由于它的弱点而被认为是杂质效应，但最近的研究表明它是由Jahn-Teller异构体引起的。大多数Mn12R晶体现在被认为是SR和FR分子的混合晶体，在Mn3+的Jahn-Teller扭曲上有结构上的差异。在SR分子中，延长的Mn3+离子的Jahn-Teller轴几乎平行于Mn12R的分子轴，而FR分子中包含一个异常的Jahn-Teller扭曲的Mn3+位。在Mn12Ph上的变角磁性测量表明，FR物种的磁易轴相对于准D4h分子轴倾斜12°，而SR分子的磁易轴平行于准D4h分子轴。即使在Mn12Me中，高压也会导致SR物种向FR的转变，在常压下，FR物种的数量可以忽略不计。对Mn11CrMe和Mn12Me近1：1混晶的结构和磁性研究表明，尽管Mn11CrMe的分子骨架中含有非Jahn-Teller离子Cr3+，但Mn11CrMe的磁各向异性与Mn12Me的磁各向异性几乎相同。
In this Feature Article, we discuss our work on the Jahn–Teller isomers in a single molecule magnet, [Mn12O12(RCO2)16(H2O)4] (abbreviated as Mn12R), and the magneto-structural correlation between them. Mn12R derivatives always exhibit two peaks at 5 and 2 K in the temperature dependence of the imaginary component of the ac susceptibility χ″, suggesting the presence of a slower relaxation (SR) process and a faster relaxation (FR) process. Although the peak at 2 K used to be regarded as an impurity effect due to its weakness, recent studies have revealed that it is caused by a Jahn–Teller isomer. Most of the Mn12R crystals are now recognized as mixed crystals of SR and FR molecules having a structural difference in the Jahn–Teller distortion at Mn3+. In the SR molecule, the elongated Jahn–Teller axes of Mn3+ ions are all nearly parallel to the molecular axis of Mn12R, while the FR molecule includes an Mn3+ site of unusual Jahn–Teller distortion. The angular-dependent magnetic measurements on Mn12Ph indicated that the magnetic easy axis of the FR species was tilted by 12° from the pseudo-D4h molecular axis, while that of the SR molecule was parallel to it. High pressure was found to bring about a transformation of the SR species into FR even in Mn12Me, in which the number of FR species was negligible at ambient pressure. The structural and magnetic studies on a nearly 1 ∶ 1 mixed crystal of Mn11CrMe and Mn12Me indicated that the magnetic anisotropy of Mn11CrMe was nearly identical to that of Mn12Me, though Mn11CrMe included a non-Jahn–Teller ion Cr3+ in the molecular skeleton of Mn12.