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

单分子磁体（SMM）领域的最终目标是制造出阻塞温度大于室温的分子。这将允许像分子存储设备这样的应用。本项目旨在通过两种方式实现这一目标。首先，探索控制SMM行为有效性的物理规律，以确定在大阻塞温度下需要优化的关键性质。我们将研究具有Me = Fe, Cr， Al的分子铁恒星家族MeFe3L6。对于FeFe3L6和CrFe3L6，将通过在0.25 K温度下施加快速磁场扫描的扭矩测量来研究与SMM行为相关的宏观量子隧穿（MQT）现象。由于这个家族的三个成员具有本质上相同的几何结构，因此比较它们的属性将有助于深入了解MQT的机制。磁各向异性对SMM的行为起着重要的作用。因此，该项目的第二个目标是研究分子簇的几何结构和磁各向异性之间的关系，以找到有助于化学家创造具有高阻断温度的分子体系的规则。这里我们将重点关注配合物MeFe3L6和Mn[3x3]-网格。由于它们的高分子对称性，它们代表了解决这个问题的理想模型系统。实验上，利用17-26 GHz高场转矩磁强计和高场EPR谱分析了磁各向异性。

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.