RECOILLESS-FRACTION RATIOS FOR FE57 IN OCTAHEDRAL AND TETRAHEDRAL SITES OF A SPINEL AND A GARNET

We have determined the ratio of recoilless fractions, fB′fA′, of Fe57 nuclei in octahedral (B) and tetrahedral (A) sites in Fe3O4 and in yttrium iron garnet (YIG), using the Mössbauer effect, by measuring the area ratios as a function of temperature. We find fB′fA′=0.99±0.01 at 0°K and fB′fA′=0.94±0.02 at room temperature. Since, in the Debye approximation, a difference in recoillesss fractions implies a difference in the Debye temperatures, we have defined two Debye temperatures for such materials corresponding to Fe ions in A and B sites. These Debye temperatures have been determined independently and are consistent with the ratio of recoilless fractions. The Debye temperatures are, however, considerably lower than those found by specific-heat measurements. Possible explanations for this difference are discussed. © 1969 The American Physical Society.