Nuclear magnetic ordening in fluorene

The present paper considers the possibility to obtain a magnetic ordering of the proton spins in molecular crystals of fluorene using dynamic nuclear polarization (DNP) followed by adibatic demagnetization in the rotating frame (ADRF). It is found that such an ordering is most easily reached for T < 0 and 80 II c-axis. Then a polarization of only 26% needs to be reached by DNP in order to obtain a ferromagnetic ordering. The importance of fluorene lies in the possibility to use photoexcited triplet states for DNP. Then, during and after the ADRF the sample is free of paramagnetic centres and a cleaner study of the ordering can be made.