Hyperfine interactions in ferrous fluosilicate

Abstract

The Mössbauer effect spectrum of ferrous fluosilicate has been measured between 1.7 and 4.2 °K in external magnetic fields of up to 30 kG for both single-crystal and polycrystalline specimens. With the field H parallel to the trigonal axis z of the crystal (for which the susceptibility is small) only a small hyperfine splitting was observed, but for H along any axis x in the plane perpendicular to z a large effective field was found. The saturation values deduced for the components of the hyperfine field tensor were Hnx(0) = -248 kG and Hnz(0) = -550 kG. The spectrum for polycrystalline specimens was almost identical with that for the single crystal with the field perpendicular to z. The data are discussed in terms of the theory of hyperfine fields, and an estimate of the effective value of <r-3> for the 3d-electron spin is made. The value of the electric quadrupole moment of the excited state of 57Fe deduced from the quadrupole splitting is re-assessed at +0.18 bn.