Moessbauer study of natural wolframites

The first Moessbauer results obtained with powdered samples of natural wolframites Fesub(x)Mnsub(1-x)WO4 from some famous Portuguese and Peruvian mines are reported here. The Moessbauer experiments have been carried out at 300, 77 and 4.2 K with four natural and one synthetic powdered samples of different compositions. The Moessbauer parameter values can be attributed to a high spin ferrous ion in a quite distorted octahedral symmetry. From the 4.2 K spectra, one deduces a weak value for the hyperfine magnetic field (Hsub(h)sub(f) approx. equal to 45 kOe), a negative sign for the quadrupole interaction, and an approximate value for the asymmetry parameter (eta approx. equal to 0.7). X-ray diffractometry experiments developed to determine the lattice constants have shown a linear behaviour of the most sensitive parameter a as a function of the iron content x. In parallel, a linear behaviour of the Neel temperature Tsub(N) with x observed between x = 0.5 and x = 1. (orig.)