MAGNETIC RESONANCES IN ONE-DIMENSIONAL SPIN SYSTEMS NENP AND NINO

We present Electron-Spin-Resonance experiments in the frequency range 35-420 GHz in magnetic fields up to 14 T and with temperatures down to 1.5 K. The quasi-onedimensional S = 1 Spin Systems NENP and NINO exhibit similar resonance-modes, which can be associated with transitions between excited states at q = pi and excitations from the groundstate. Groundstate-excitation can be explained with regard to a transverse staggered field due to inequivalent Ni2+-sites along the chains. Several features are discussed like polarisation-and temperature dependence of line-intensity and the angular and temperature-dependence of resonance-field.