High-field/high-frequency EPR studies of spin clusters with integer spin: the multi-frequency approach

In this paper a rapid overview of the main results obtained from the study with multi-frequency HF-EPR of molecular spin clusters possessing integer spin values is presented. In the first part, two antiferromagnetic rings with zero ground spin state are reported. It is illustrated how the HF-EPR study of the first excited states allows obtaining important information on this kind of spin clusters. In the second part, selected examples of single-molecule magnets (SMM) are treated, starting with complexes involving only a few magnetic ions and going on to more complex systems. Indeed, because of their large zero-field energy gaps, EPR studies of SMM deserve the use of high frequencies and high fields. The approach presented here is twofold. First the interest of studying a series of 'simple' SMM in order to understand the subtle mechanisms underlying their properties is stressed. Then a summary of our HF-EPR studies of the most investigated SMM, Mn12ac and Fe8 is presented.