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

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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.