ELECTRON-PARAMAGNETIC-RESONANCE DETECTION OF SOLITONS IN 2-DIMENSIONAL MAGNETS

It has previously been assumed that spin waves were the dominant excit ations in lower-dimensional magnets. Recently, however, it has been sh own that nonlinear excitations or solitons rather than spin waves infl uence the dynamic thermal quantities such as the spin correlation func tion which can be investigated experimentally through the electron par amagnetic resonance linewidth. In this review the influence of both sp in waves and solitons on the temperature-dependent linewidth in the fl uctuation region immediately above the ordering temperature is discuss ed. It is seen that both excitations result in a theoretical Arrhenius temperature-dependence, (Delta H similar to exp(E/T) where E = 6 pi J s(2) for spin waves and E = 4 pi Js(2) for solitons, J is the nearest neighbor exchange constant, and s is the Value of the spin. In experim ents, quantum (s = 1/2) layered copper compounds exhibit the temperatu re dependence expected from spin waves even though nonlinear excitatio ns have been shown to exist in these systems. On the other hand nearly classical (s = 5/2) manganese compounds have the temperature dependen ce expected from solitons. The calculation of the linewidth from both spin waves and solitons is reviewed and compared with experimental dat a to show that solitons dominate the dynamics of the layered, nearly c lassical magnet.