Magnetic Studies on the 1-D Antiferromagnetic Chains of enH2Mn(Fe)F5

M easurem ents of the 57Fe M össbauer effect and of m agnetic susceptibilities have been perform ed on the 57Fe doped or pure quasi-l-d antiferrom agnetic chain com pound en H 2 M nF 5 as a function of tem perature. Particular a ttention was paid to the regions very n ear the Neel point at T N = 14.5(5) K. The M össbauer spectra fitted by the Blum e-Tjon m odel show definite relaxation effects, which are a ttribu ted to short-range o rder with tem per­ a tu re-dependent relaxation times. The soliton m odel of non-linear excitations was applied. E xperim ental data confirm the predicted exponential tem perature dependence of the th e r­ mal 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 ob­ tained which is sm aller than D/k = -3 .5 K derived from our single crystal m easurem ents of m agnetic susceptibilities. W ithin the 3-d m agnetic ordering the interchain interaction am ounts to J '/k ~ 0.22(4) K (J '/J = 15.8 10“3). A zero-spin reduction zlS/S equal to 17% was obtained. 1-d correlations are observed for T N< T < I JIS (S + l)/k ~ 78 K, and a crystallo­ graphic phase transition at 216 K was indicated in the m agnetic p roperties as well as by DSC and X-ray pow der diffraction m easurem ents.