Forces on spins in a field gradient: apparent spin relaxation

A magnetic field gradient exerts opposite forces on spin magnetic moments oriented up and down. The result is to partially segregate spins by orientation, with more spins-up at one end of the sample and more spins-down at the other. This apparent relaxation, involving only sorting and no flipping of spins, may be dominant in systems of high diffusivity and long T$_{1}$. The sorting mechanism competes with a well-known distinct, true T$_{1}$ mechanism driven by diffusion through field gradients. The results of our calculations and numerical solutions of the Bloch-Torrey equations, modified to include the force term, will be presented in detail.