MAGNETIC AND MOSSBAUER-EFFECT STUDY OF THE CLUSTER DISTRIBUTION FUNCTION IN THE SPIN-GLASS PHASE THETA-ME0.35V2O5 (ME=FE,AL)

Moessbauer data reveal for the vanadium oxide bronzes theta -Fe//0 //. //3//5V//2O//5 and theta -Al//0//. //2//6Fe//0//. //0//9V//2O//5 a randomly oriented spin arrangement with only weak indirect exchange interaction possibly simulating a spin-glass like order. Below 18 K the onset of magnetic order shows up in broadened magnetic hf patterns. One observes two sixline spectra below 6 K. The Moessbauer patterns can be successfully fitted assuming superparamagnetic relaxation of a cluster magnetization. The relaxation model is appropriate for a flipping of the hf field into a reversed direction. From the resolved spectra it is apparent that clusters with different relaxation frequencies w(1) equals 4. 0 MHz/w(2) equals equals 0. 9 MHz and different hf fields H(1) equals 45. 0 T/H(2) equals 38. 5 T are present. The cluster distribution function is derived from the temperature dependence of the relative intensity D of the doublets.