Magnetic Solitons in the 1-D Antiferromagnetic Chains

Prof. Dr. Kurt Dehnicke zum 65. Geburtstag gewidmet Measurements of the 5 7 Fe Mössbauer effect and magnetic susceptibility have been performed on 5 7 Fe-doped quasi-l-d antiferromagnetic chains of L i 2 MnF 5 and Na 2 MnFg as a function of temperature. The Mössbauer spectra, fitted by the Blume-Tjon model, show definite relaxation effects near the Neel temperature, which are attributed to short-range order with temperature-dependent relaxation times. The soliton model of non-linear excitations was applied. Experimental data confirm the predicted exponential temperature dependence of the thermal excitation of moving domain walls. F r o m the activation energies EJk as a function of 1-d exchange energies J/k the local anisotropy energy D/k of —3.7(2) K was derived on the basis of sine-Gordon theory. This result is in fair agreement with —3.5(1) K previously derived f rom magnetic susceptibility measurements. In the light of our results there is some evidence that at low bridging angle ß % 102(5)° a phase-transition f rom antiferromagnetic to ferromagnetic ordering occurs.