Effective Field Parameters in Iron Mössbauer Spectroscopy

Abstract

Relatively simple computational methods for interpreting Mössbauer spectra, in which there are simultaneously static quadrupole and hyperfine interactions, have been developed. Our explicit calculations are restricted to the case when either the source or absorber is a ``single line'' and the nuclear levels are the same as in the 57Fe 14.4-keV transition. Experimental spectra for powdered RbFeF3 and FeCr2S4 have been obtained and are analyzed using these methods. Our results show that although the quadrupole interaction ΔEQ is zero above the transition temperatures of both RbFeF3 and FeCr2S4 it is rather large below, i.e., in FeCr2S4, ΔEQ=0.78 mm/sec at 77° K and in RbFeF3, ΔEQ=3.00 mm/sec at 4°K. The isomer shift, the effective internal magnetic field, and its orientation with respect to the principal axes of the electric-field-gradient tensor in these substances at various temperatures are also obtained.

Spin re-orientation in FeCr2S4

“…2 Temperature dependence of hyperfine magnetic field B hf field gradient appears which is increasing with increasing magnetic hyperfine field as already described earlier [3]. The observation of a quadrupole interaction at iron below the Curie temperature despite neutron data prove cubic structure has been discussed controversially [1,2,[5][6][7][8][9][10][11]. As first proposed by [2] this quadrupole interaction can be related to a magnetically induced electric field gradient.…”

“…The thiospinel FeCr 2 S 4 has been studied since very early days of Mössbauer spectroscopy [1][2][3]. Magnetic order has been found below about 160 K [4].…”

Hyperfine interactions in szomolnokite (FeSO4·H2O)

“…For the analysis of the magnetic spectra, an iteration procedure was applied that is based on the diagonalization of the full nuclear hyperfine-interaction hamiltonian, taking into account combined electric and magnetic hyperfine interactions, the strengths of which are of the same order of magnitude. Assuming a random powder absorber, the relevant nuclear energy levels for the 57 Fe isotope and the transition probabilities between these levels can be determined using this method [11,12], and subsequently the theoretical MS can be calculated using Lorentzian-shaped absorption lines. The energy values of the relevant nuclear levels and consequently the positions (in mm/s) of the absorption lines are thus determined by the hyperfine parameters: the center shift d, the principal component V zz (which is related to the quadrupole splitting -see later) of the electric field gradient (EFG), the asymmetry parameter g of the EFG, and the strength B hf of the magnetic hyperfine field, and further by the zenithal (X) and azimuthal (w) angles of the hyperfine field in the EFG (x,y,z)-axes frame (see Fig.…”

Magnetic-field-induced quadrupole splitting

“…First we consider the case in which the transition metal ion is in an applied magnetic field. To calculate v, 7 and P we compare an appropriate matrix element [4] using both hamiltonians, (1) and (2). We shall illustrate the method of calculating (EQ) for a d a ion in a strong crystal field of octahedral symmetry, in which case the crystal-field axis is parallel to the applied magnetic field.…”

“…Recently [1,2] a magnetic-field-dependent quadrupole splitting has been observed in the M6ssbauer spectrum of high-spin ferrous ion where the ferrous ion is in a weak crystal field of octahedral symmetry. Above the N6el temperature only a single gamma-ray absorption band was found.…”