Anisotropic hyperfine fields in FeSn by Mossbauer spectroscopy

Abstract

57Fe and 19Sn Mossbauer investigations of the antiferromagnetic compound FeSn are reported from 77K to well above its magnetic transition temperature. The observation of a single nuclear Zeeman pattern from 1(a) Sn sites implies that the spin ordering in the basal plane is collinear. The 57Fe Mossbauer studies show that, whereas in the paramagnetic state the observed spectrum is a well-defined single quadrupole doublet, the spectrum in the magnetic state is quite complex due to the presence of a system of three different local principal electric-field gradient (EFG) axes for the crystallographically equivalent Fe atoms which are characterised by significantly different anisotropic nuclear hyperfine fields. It is found that the magnitudes of the observed hyperfine fields can be explained satisfactorily in terms of an isotropic contribution hiso and enhanced dipolar fields originating from the external magnetic moments with a single enhancement factor of about 8.2, for the three nuclear Zeeman patterns simultaneously. The value of hiso has been estimated as a function of temperature. On the basis of the above model, the direction of the nuclear hyperfine field should deviate from the direction of magnetisation due to the presence of an appreciable component of the enhanced dipolar fields in a direction perpendicular to the direction of magnetisation.