High spin cycles: topping the spin record for a single molecule verging on quantum criticality
High spin cycles: topping the spin record for a single molecule verging on quantum criticality
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DOI：
10.1038/s41535-018-0082-7
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发表时间：
2018-02-26
影响因子：
5.7
通讯作者：
Powell, Annie K.
中科院分区：
文献类型：
--
作者：
Baniodeh, Amer;Magnani, Nicola;Powell, Annie K.
将短链环化成环提供了将有限自旋阵列转化为准无限结构的迷人场景。如果存在挫折，理论预测有趣的量子临界点，在那里，即使适当的外部参数发生很小的变化，材料的基态和低温特性也会发生急剧变化。这可以被想象为达到一个非常高和尖锐的顶峰，在那里向下的路有无限的可能性，通过任何参数的变化将迅速选择，以达到最终的基态。在这里，我们报告一个混合的3d/4f循环配位簇，原来是非常接近，甚至在这样的量子临界点。它的基态自旋为S = 60，是有史以来观察到的最大分子（是单个电子的120倍）。[Fe 10 Gd 10（Me-tea）（10）（Me-teaH）（10）（NO3）（10）]中心点20 MeCN形成具有交替的钆和铁离子的纳米环面，其具有最近邻Fe-Gd耦合和令人沮丧的次最近邻Fe-Fe耦合。这样的自旋排列对应于循环三角形或锯齿链，其可以表现出不寻常的挫折效应。在目前的情况下，量子临界点承载着数万个能量简并状态的“平地”，在这些状态之间的转换是可能的，而不需要能量成本，并产生深刻的热量后果。从熵的角度来看，能量平原转化为俯瞰熵景观的尖顶。走下坡路，几个目标状态可以达到取决于所应用的物理过程，这提供了新的前景寻址。
The cyclisation of a short chain into a ring provides fascinating scenarios in terms of transforming a finite array of spins into a quasiinfinite structure. If frustration is present, theory predicts interesting quantum critical points, where the ground state and thus low-temperature properties of a material change drastically upon even a small variation of appropriate external parameters. This can be visualised as achieving a very high and pointed summit where the way down has an infinity of possibilities, which by any parameter change will be rapidly chosen, in order to reach the final ground state. Here we report a mixed 3d/4f cyclic coordination cluster that turns out to be very near or even at such a quantum critical point. It has a ground state spin of S = 60, the largest ever observed for a molecule (120 times that of a single electron). [Fe10Gd10(Me-tea)(10)(Me-teaH)(10)(NO3)(10)]center dot 20MeCN forms a nano-torus with alternating gadolinium and iron ions with a nearest neighbour Fe-Gd coupling and a frustrating next-nearest neighbour Fe-Fe coupling. Such a spin arrangement corresponds to a cyclic delta or saw-tooth chain, which can exhibit unusual frustration effects. In the present case, the quantum critical point bears a 'flatland' of tens of thousands of energetically degenerate states between which transitions are possible at no energy costs with profound caloric consequences. Entropy-wise the energy flatland translates into the pointed summit overlooking the entropy landscape. Going downhill several target states can be reached depending on the applied physical procedure which offers new prospects for addressability.