The mössbauer spectrum of almandine

Mössbauer spectra of a synthetic, pure almandine (Alm₁₀₀) and a natural almandine-rich garnet (Alm₈₆) were taken at temperatures between 295 and 4.2 K. Different widths and depths of the lines observed in the paramagnetic state require the spectra to be fitted with at least two components of slightly different quadrupole splittings and isomer shifts. Alm₁₀₀ shows a gradual onset of magnetic order between 10.4 and 9.0 K, with about 50 percent of the sample magnetically ordered at 9.6 K. At 4.2 K both samples have complex spectra that can be fitted by two eight-line magnetic hyperfine patterns of equal intensities. These result from the existence of two different polar angles between the z-axis of the electric field gradient and the direction of the magnetic hyperfine field, or from two distinctly different electric field gradients. The former interpretation, in which the two angles are attributed to a modulated, non-collinear spin arrangement, is considered more likely. Both magnetic components have practically identical quadrupole splittings, 1/2eQV _zz (1+η²/3)^1/2, that average ?3.70 mm·s^?1, and a small asymmetry parameter of η=0.07. Alm₁₀₀ has a magnetic hyperfine field of 25.7 T at 4.2 K, whereas Alm₈₆ has a hyperfine field of only 23.3 T; the other features of the spectra of both samples are similar.