Nanomagnets with high molecular symmetry: ground state spin, anisotropy and macroscopic quantum tunneling

单分子磁体(SMM)领域的最终目标是创造出阻挡温度高于室温的分子。这将使分子存储设备等应用成为可能。该项目旨在通过两种方式实现这一目标。首先，应该探索控制SMM行为有效性的物理规律，以便确定必须针对较大的阻塞温度进行优化的关键特性。我们将研究分子铁星MeFe3L6家族，其中Me=Fe，Cr，Al。对于FeFe3L6和CrFe3L6，与SMM行为相关的宏观量子隧道(MQT)现象应通过在0.25K温度下应用快速磁场扫描进行扭矩测量来研究。由于这一家族的三个成员具有基本相同的几何结构，因此对它们的性质进行比较将有助于对MQT的机制有更深入的了解。已知磁各向异性对SMM行为起着重要作用。因此，本项目的第二个目标是研究分子团簇的几何结构与磁各向异性之间的关系，以找到有助于化学家创建具有高封闭温度的分子体系的规律。在这里，我们将重点关注络合物MeFe3L6，但也关注一个Mn[3x3]-格子。由于它们的高分子对称性，它们是解决这一问题的理想模型体系。在实验上，我们将在17-26 GHz用高场扭矩磁强计和高场EPR谱研究磁体的各向异性。

The ultimate goal in the area of single molecule magnets (SMM) is to create molecules with blocking temperatures larger than room temperature. This would allow applications like e.g. molecular storage devices. This project aims to approach this goal in two ways. First, the physical laws controlling the effectiveness of the SMM behavior shall be explored in order to identify the key properties which have to be optimized with respect to large blocking temperatures. We will investigate the family of molecular ferric stars MeFe3L6 with Me = Fe, Cr, Al. For FeFe3L6 and CrFe3L6, the phenomenon of macroscopic quantum tunneling (MQT) associated with SMM behavior shall be investigated by torque measurements at temperatures of 0.25 K applying fast magnetic field sweeps. Since the three members of this family have essentially identical geometrical structures a comparison of their properties will allow deep insights into the mechanism of MQT. The magnetic anisotropy is already known to play an important role for SMM behavior. Thus, a second aim of this project is to study the relationship between geometrical structure and magnetic anisotropy of molecular clusters in order to find rules which will help chemists to create molecular systems with high blocking temperatures. Here we will focus on the complexes MeFe3L6 but also on a Mn[3x3]-grid. Due to their high molecular symmetries, they represent ideal model systems to address this question. Experimentally, magnetic anisotropy will be investigated by high-field torque magnetometry and high-field EPR spectroscopy at 17-26 GHz.