Spin Diffusion and Spin–Lattice Relaxation in the Zeeman and Dipolar Systems

Relaxation in the Zeeman and dipolar spin systems is considered. To shorten the spin–lattice relaxation time in the samples containing paramagnetic impurities, we propose to transfer order from the Zeeman to the dipolar systems. The diffusion equations for the inverse Zeeman and dipolar spin temperatures are solved numerically. It is shown that the dipolar system relaxes faster than the Zeeman one. At the initial stage, the relaxation in the Zeeman and dipolar spin systems is nonexponential. Then, the relaxation regimes in both cases are asymptotically changed to be described by exponential functions of time. The acceleration of the relaxation is achieved due to the following factors: the diffusion coefficient of the dipolar energy is larger than one of the Zeeman energy, and the energy transfer from the Zeeman system into the dipolar one allows us to overcome the obstacle of the diffusion barrier.