Mössbauer study of natural wolframites

The first Mössbauer results obtained with powdered samples of natural wolframites Fe _x Mn_1?x WO₄ from some famous Portuguese and Peruvian mines are reported here. The Mössbauer experiments have been carried out at 300, 77 and 4.2 K with four natural and one synthetic powdered samples of different compositions. The Mössbauer 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 (H _hf?45 kOe), a negative sign for the quadrupole interaction, and an approximate value for the asymmetry parameter (η?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 Néel temperature T _N with x observed between x=0.5 and x=1.