MAGNETIC STUDIES ON THE 1-D ANTIFERROMAGNETIC CHAINS OF ENH(2)MN(FE)F-5

Measurements of the Fe-57 Mossbauer effect and of magnetic susceptibil ities have been performed on the Fe-57 doped or pure quasi-1-d antifer romagnetic chain compound enH(2)MnF(5) as a function of temperature. P articular attention was paid to the regions very near the Neel point a t T-N = 14.5(5) K. The Mossbauer spectra fitted by the Blume-Tjon mode l show definite relaxation effects, which are attributed to short-rang e 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. From the activation energy E(A)/k = 184(5) K and the 1-d exchange energy J/k = -13.6(2)K a local anisotropy energy D/k of -2.4 (3) K was obtained which is smaller than D/k = -3.5 K deri ved from our single crystal measurements of magnetic susceptibilities. Within the 3-d magnetic ordering the interchain interaction amounts t o J'/k approximate to 0.22(4) K (J'/J = 15.8 10(-3)). A zero-spin redu ction Delta S/S equal to 17% was obtained. 1-d correlations are observ ed for T-N<T<\J\S(S+1)/k approximate to 78 K, and a crystallographic p hase transition at 216 K was indicated in the magnetic properties as w ell as by DSC and X-ray powder diffraction measurements.