Magnetic Solitons in the 1-D Antiferromagnetic Chains of Li2Mn0.98Fe0.02F5 and Na2Mn0.98Fe0.02F5

Abstract

Abstract Measurements of the 57Fe Mössbauer effect and magnetic susceptibility have been performed on 57Fe-doped quasi-1-d antiferromagnetic chains of Li2MnF5 and Na2MnF5 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 relax-ation 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. From the activation energies E2 A/k2 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 from magnetic susceptibility measurements. In the light of our results there is some evidence that at low bridging angle ß ≈ 102(5)° a phase-transition from antiferromagnetic to ferromagnetic ordering occurs.