The influence of paramagnetic impurities on the dynamic polarization of protons in (La, Nd)2Mg3(NO3)12.24H2O

Abstract In single crystals of La 2 Mg 3 (NO 3 ) 12 .24H 2 O containing 2.0% Nd and 0.02% to 0.50% Ce the proton dynamic polarization factor and the polarization time have been measured. The results are compared with the predictions on the basis of Borghini's spin temperature theory including the influence of the factor f . Most of the results can be explained by assuming that nuclear spin diffusion is very fast, so that the main part of the proton spin system is in internal equilibrium. Only when the leakage of polarization due to the Ce ions is very important, the dependence of the enhancement factor on microwave power indicates that spin diffusion is not fast enough to maintain equilibrium in the proton spin system.