Nuclear Magnetic Relaxation of1H in the Organic Radical Saltsm-MPYNN+·ClO4-andm-MPYNN+·BF4-

Abstract

We have measured nuclear spin-lattice relaxation times T 1 of 1 H in the organic salts m -MPYNN + ·ClO 4 - and m -MPYNN + ·BF 4 - in the temperature range between 2 K and 100 K under external fields up to 70 kOe. In these salts, two cationic (spin-1/2) radicals constitute a dimer due to the ferromagnetic interaction J 1 . We interpreted the experimental results of T 1 -1 below about 10 K (∼ J 1 / k B ) in terms of two relaxation processes based on the energy levels of the ferromagnetic dimer. The flip-flop and the direct processes which are due to longitudinal and transverse spin fluctuations become dominant at higher and lower fields, respectively, the crossover field being around 10 kOe. For the field dependence of T 1 -1 at higher temperatures, the spin diffusive model of spin-1/2 in a two-dimensional system is satisfactorily applied.