Slow relaxation of the magnetization in rationally designed single-chain magnets

After the intense research activity in the field of slow dynamics of the magnetization in molecular clusters (SMMs) and the bistability related problem, the field of Molecular Magnetism is currently shifting towards more complicated systems. One direction has been opened by the observation of slow relaxation of the magnetization in 1D systems (called Single Chain Magnets or SCMs). Synthetic efforts are devoted to the development of new systems SCMs that can help us understanding the physical background that lies beneath this phenomenon. In this contest several groups have development new tools allowing for the engineering of both magnetic and structural properties. Here we discuss some opportunities offered by the Metal Nitronilnitroxyde strategy. In particular the experimental and theoretical work developed on finite-size effects revealed itself a key point. We describe the rational strategy that allowed creating the first rare-earth based SCMs. We show that we can freely substitute the metallic centres without structural alterations, thus tuning of the magnetic properties. This affords a useful information on the key parameters that rule SCMs.