Half-field EPR transition in the one-dimensional paramagnet tetramethylammonium-manganese-trichloride (TMMC)

We report the observation of a half-field transition in the EPR spectrum of tetramethylammonium-manganese-trichloride (TMMC). The observation of this new resonance is a direct consequence of the one-dimensionality of the spin dynamics of this manganese salt. We present a theory which accounts for many of the observed features in a very satisfactory way. The experiments are performed with the microwave field parallel to the static magnetic field. The most important characteristics of the transition are the scaling of the linewidth with the EPR spectrum obtained with the microwave field perpendicular to the static magnetic field, and its highly anisotropic intensity.