Lowest Fe2+spin excitations in disordered Fe1-xMnxCl2mixtures by microwave absorption at high frequencies

Abstract
Far-infrared absorption measurements in Fe1-xMnxCl2 are reported in the frequency range 60 to 600 GHz. The low-energy excitations of the Fe2+ spin system have been studied at low temperature over the whole range of concentration. At low Mn2+ concentration, in both antiferromagnetic and ferromagnetic phases, the authors observe a resonance line corresponding to the excitation of antiferromagnetic and ferromagnetic magnons. For x1(Fe-Fe)=1010 GHz. For larger concentrations (0.151<or=x0.5 the absorption signal becomes very broad.