Mössbauer study of the hyperfine magnetic field and electric field gradient at Fe sites in synthetic diamond.

Abstract

Mossbauer Spectroscopy has been used to investigate the site of Fe inclusions in a suite of synthetic diamonds (de Beers MDAS). Information on the hyperfine magnetic fields and electric field gradients at Fe sites in the diamond grains were obtained from Mossbauer Spectroscopy of diamond grains ranging in size from 25 to 250 um. The Fe inclusions in these samples resulted from the synthesis of the diamond grains in which Fe was used as a catalytic solvent. The Mossbauer measurements were carried at room temperature with a constant acceleration spectrometer operating in transmission geometry. The samples with the largest grain size of 180-250 um gave a well defined six component magnetically split spectrum, similar to the Zeeman split sextet obtained for natural iron. As the grain sizes decreased the intensity of the magnetically split components became greatly reduced and a strong paramagnetic component appeared. At grain sizes 105-45 um the spectra are dominated by a central single line with some evidence of an asymmetric doublet. For the finest grain size 38-25 um, the reappearance of the six magnetic hyperfine splitting components together with the strong central single paramagnetic component was observed. The change in the Mossbauer patterns observed with decreasing grain size suggest that a rapid phase transition of the Fe inclusions from ferromagnetic to superparamagnetic takes place. The analysis of Mossbauer spectra yielded a value of the hyperfine magnetic field of Bhf = -32.4(4) T and an electric field gradient in the range of Vzz = 1.4(4) 1.8( 7) X 10'8 V.cm- 2 at the site of the probe s7Fe nucleus. These values compare favourably with other measurements.