MAGNETIC-RESONANCE OF 2-DIMENSIONAL HEISENBERG ANTIFERROMAGNETS WITH NONMAGNETIC IMPURITIES

The EPR linewidths of (C3H7NH3)2Mn1-xCdxCl4 have been measured in the paramagnetic region as a function of temperature. An Arrhenius behavio r exp(b/T) is observed with b strongly dependent on Cd concentration. This behavior in the pure compound is characteristic of soliton-like ( skyrmion) excitations with b related to the excitation energy. In the doped compound, gapless nonlinear excitations are possible, resulting in a much different temperature-dependent linewidth. It is concluded t hat skyrmions dominate the low-temperature thermodynamics of two-dimen sional magnets.