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Hyperfine fields and the electric field gradient (EFG) were experimentally obtained, in temperature interval of 4.2 K to 700 K for the Laves phase intermetallic compound HfFe2 and for the pseudo binary compounds HfFe2-xSi with x = 0.05, 0.1 and 0.3 using 57Fe Mössbauer effect spectroscopy. As was recently reported /1/, the addition of Si results in the stabilization of the cubic Cl5 phase of HfFe2 for concentrations 0.05 < x < 0.24. Since this stabilization could be the result of the charge and spin density perturbations by Si in the HfFe2 matrix, an analysis of the 57Fe Mössbauer data was made to determine these quantities at the Fe site. The magnetic hyperfine fields obtained at 300 K for the compound HfFe2 were 179 ± 2 kOe and 173 ± 3 kOe with a population ratio of 3 : l for the two magnetically non-equivalent sites in the Cl5 structure. For the compound x = 0.1, three hyperfine fields were measured at 4.2 K : 218 ± 3 kOe, 205 ± 3 kOe and 175 ± 5 kOe. The smallest field is associated with iron atoms that have Si as a first nearest neighbor. The mean saturated hyperfine fields for both x : 0.05 and 0.10 are larger than for HfFe2. Furthermore our measurements indicate that the magnetic transition temperature is also larger for these alloys than for HfFe2. For x = 0.3, the structure is hexagonal Cl4 and both the hyperfine field and transition temperature decrease. In addition, the spectra show evidences of a distribution of hyperfine fields. The quadrupole splitting measured above the Curie temperature was 0.32 mm/s for HfFe2 increasing to 0.38 mm/s for the compound with x = 0.1. For x = 0.3, a decrease in the splitting was observed. No direct evidence for more than one quadrupole interaction was seen for any of the compounds studied. In addition the isomer shift increases with increasing Si content up to the maximum concentration studied. An interpretation of these results is given in which the Si provokes an overall reduction in the mean electronic density through shielding effects. This would be supported by the increase in localized d character on those Fe which are not nearest neighbors of Si and the reduction of the average s-electron density indicated by the isomer shift results. The exact nature of the shielding may involve band electrons and localized ones on Fe which are nearest neighbors of Si

57Fe MÖSSBAUER EFFECT STUDY OF HYPERFINE INTERACTIONS IN HfFe2-xSix

⁵⁷Fe MÖSSBAUER EFFECT STUDY OF HYPERFINE INTERACTIONS IN HfFe_2-xSi_x