Covalency effect in paramagnetic relaxation

The effect of covalency on the spin–lattice relaxation of an iron-group ion in octahedral coordination is examined. It is found that the covalent contribution to the spin–phonon Hamiltonian is predominantly "dipolar", but probably too small to cause a measurable violation of the quadrupolar selection rules for [Formula: see text] ions at and below JV-band frequencies. For an ion with a low-lying spin doublet, the covalent contribution could be important.