Spin Diffusion and Relaxation in a Nonuniform Magnetic Field
  We consider a quasiclassical model that allows us to simulate the process of spin diffusion and relaxation in the presence of a highly nonuniform magnetic field. The energy of the slow relaxing spins flows to the fast relaxing spins due to the dipole-dipole interaction between the spins. The magnetic field gradient suppresses spin diffusion and increases the overall relaxation time in the system. The results of our numerical simulations are in a good agreement with the available experimental data. 
G.P. Berman, B. M. Chernobrod, V.N. Gorshkov, V.I. Tsifrinovich