Spin-Spin Relaxation

This involves energy transfer between interacting spins via dipole and exchange interactions. The relaxation rate depends heavily on the concentration of paramagnetic ions in the sample. This mechanism is largely temperature independent. The relaxation rate can be expressed as

$$R \propto \vert \langle i\vert\mathcal{H}\vert f \rangle \vert^{2} \phi$$ (2.27)

where $i$ and $f$ are the initial and final spin states, $\mathcal{H}$ is the Hamiltonian of the mechanism and $\phi$ is a phase factor.