Project B4: Exploration of the Magnetic Properties and Exotic Behavior of 3d/4f Coordination Clusters

DFG Research Areas: Condensed Matter Physics, Molecular Chemistry, Physical Chemistry, Analytical Chemistry

The aim of the project is to explore the magnetic properties including exotic behavior in 3d/4f coordination clusters with an emphasis on systems combining Fe/4f and 3d/Dy ions. Relevant examples of exotic magnetic behavior are found in molecules showing toroidal moments. These were first identified on a molecular basis in a collaboration with the Mercator fellow Prof. Roberta Sessoli (University of Florence, Italy). These systems could be developed into multiferroic or even Skyrmionic system. The emerging set of Fe/Dy molecules show the characteristics of so-called (exchange) coupled Spring Magnets.
Such coordination clusters can combine large numbers of unpaired electrons contributed by metal ions with different single ion properties (spin, orbital and spin-orbit-coupling) defining the overall magnetic properties. The nature of the magnetic coupling in these systems is not well-understood as can be illustrated by comparing isostructural series of 3d/4f coordination clusters. Variations in magnetic properties, such as the nature of slow relaxation of the magnetization and the shapes of hysteresis loops as measured on arrays of oriented single crystals using the microSQUID technique, can be observed. Currently it is challenging to rationalise this via magnetostructural correlations because of restrictions imposed by the huge size of the Hilbert space. A multi-technique approach helps since results from measurements run over different timescales can be compared. The properties of randomly oriented bulk versus oriented single crystal samples can also be explored. Nuclear-based spectroscopic methods, e.g. 57Fe Mössbauer and the recently developed 161Dy NFS (Nuclear Forward Scattering – a frequency domain Mössbauer approach) spectroscopy help and High-Frequency Electron Paramagnetic Resonance (HF-EPR) and pulsed spectroscopic measurements provide information on the bulk cooperative and relaxation behaviors.
The objectives are to develop rational and directed synthesis of suitable Fe/4f and 3d/Dy clusters with designed secondary characteristics such as possibilities for surface deposition or gas phase investigations. In parallel, new microSQUID instrumentation with better performance as indicated by faster sample turnaround times; higher applied magnetic fields; better sensitivity; as well as improved automation will be constructed. In addition, EPR techniques will be integrated into the same instrumentation, allowing us to make combined measurement on the same crystal of Single Molecule Magnets (SMMs). 

Project leaders: 
Prof. Dr. Annie Powell (KIT) 
Prof. Dr. Wolfgang Wernsdorfer (KIT)