[1] This permits polarization differences within the sample to be reduced on a timescale much shorter than relaxation effects.
The process is driven by dipolar coupling, and is therefore related to internuclear distances.
Spin diffusion has been used to study many structural problems in the past, ranging from domain sizes in polymers and disorder in glassy materials to high-resolution crystal structure determination of small molecules and proteins.
In solid-state nuclear magnetic resonance, spin diffusion plays a major role in Cross Polarization (CP) experiments.
As mentioned before, by transferring the magnetization (and thus the population) from nuclei with different values for the spin-lattice relaxation (T1), the overall time for the experiment is reduced.