Magnetically Induced Quadrupole Interactions in FeCr2S4

Abstract

The effective-field parameters at ${\mathrm{Fe}}^{57}$ nuclei in the cubic normal spinel Fe${\mathrm{Cr}}_2$ ${\mathrm{S}}_4$ have been investigated in the temperature range from 60 to 298°K, using the Mössbauer effect. A nonzero quadrupole interaction appears below the effective-magnetic-field transition temperature (≈172°K). The values of the effective internal magnetic field $H$, the electric field gradient, and the relative orientation of H with respect to the principal axes of the electric-field-gradient tensor (EFG) are determined as a function of temperature; e.g., at 77°K, $H=202\mathrm{}$ kG, $\frac{1}{2}{e}^{2}qQ=-0.62\mathrm{}$ mm/sec, and the asymmetry parameter $\eta =0.4\mathrm{}$. Predictions based on the theory of a magnetically induced quadrupole interaction do not explain the observed spectra. Assuming $H\propto {(1-\frac{T}{T_N})}^{\beta }$ near the critical point, $\beta =\frac{1}{3}$ gives a better fit to the experimental data than $\beta =\frac{1}{2}$.