Abstract
A general formula is derived for the direct spin‐lattice relaxation process of paramagnetic ions with S = ½ for arbitrary orientations of an external magnetic field relative to the crystal axes. Using the formula obtained, T1 of Cu2+ ions in square planar coordination geometries is calculated in the point charge approximation. The temperature, concentration, and angular dependence of T1 of Cu2+ ions in Ni(II)bis(diethyl‐dithiocarbamate) single crystals are reported. Including some features of covalency a reasonable agreement between the theoretical and experimental values of T1 is reached.