Cobalt(II)-Nitronyl Nitroxide Chains as Molecular Magnetic Nanowires

The observation of slow magnetic relaxation in molecular clusters is now considered as one of the most important achievements of molecular magnetism of the last few years. In fact systems like Mn12, Fe 8 have provided unique opportunities for the investigation of molecular magnetic hysteresis, quantum tunneling of the magnetization, and of phase interference (Berry phase). All these features depend on slow magnetic relaxation. While clusters can be considered as zero-dimensional materials, in principle slow relaxation of the magnetization can also be expected in one-dimensional (1D) materials, as suggested by Glauber in 1963. However, to date, it has not been possible to observe this behavior because no suitable experimental system has been produced. In fact the conditions to be met to observe slow magnetic relaxation in 1D materials are rather stringent: 1) the ratio of the interaction within the chain, J, and that between chains, J', must be rather high, larger than 10^4 ; 2) the material must behave as a 1D Ising ferro- or ferrimagnet. We have now found that slow relaxation of the magnetization and hysteresis effects which are not associated with three-dimensional (3D) order can be observed in [Co(hfac)2(NITPhOMe)]. We have shown here that these findings provide an experimental confirmation of Glauber's prediction and that magnetic bistability and the related memory effect can indeed be observed in such a 1D material without requiring any interchain interaction. These results may open exciting new perspectives including that of storing information in a single magnetic polymer as well as in the novel class of 1D materials where ionic structures are obtained inside carbon nanotubes.