Figure 1. Pulsed EPR nutation spectrum of doped PN polymer. Every spin multiplicity S corresponds to given nutation frequencies. Here electron spins are coupled in pure S=2 state with no S=1/2 remaining
In the 1990 years several groups tried to design purely organic polymers with collective magnetic properties (ideally with a ferromagnetic transition). The best result in this field was reported in 2001 by Rajca et al, who obtained a high-spin (S~5000) polymer exhibiting some of the properties of spin glasses. Unfortunately the spin bearing moieties in this material are chemically stable only at low temperature (T<100K) which precludes the development of potential applications in the field of organic electronics. Two groups at INAC (SCIB/LRM and SPrAM/LEMOH) are currently working with polymer chemists from the Warsaw University of Technology to design new polymers derived from polyaniline with spin bearing units chemically stable at room temperature.
Figure 2. Samples of doped polymers for different doping rates (darker samples correspond to higher doping rates). These samples were studied using the small-angle neutron scattering experiment PACE (LLB,Saclay) to investigate the relationships between magnetic properties and the polymer conformations.
Magnetic studies (pulsed EPR, SQUID) combined with DFT calculations performed at INAC help designing the synthesis of these new polymers towards structures that both enhance high-spin states and improve the chemical stability of spin bearing units. Recently linear polyanilines with high-spin state (S=2 in the example shown Figure 1) and spin bearing units stable several hours at room temperature were obtained. The next studies will focus on 1/ the enhancement of such a chemical stability , 2/ the relationships between the magnetic properties and the conformation of the polymer chain (see Figure 2) and 3/ the study of the magnetic properties of these polymers in thin films or in crystal phase.
Last update : 10/09 2013 (845)