A recent study of (SmGd)Fe 14Si3 showed an anomalous x-ray diffraction pattern [P. C. Ezekwenna, G. K. Marasinghe, J.-H. Nam, W. J. James, W. B. Yelon, M. Ellouze, and Ph. I'Héritier, J. Appl. Phys. 87, 6716 (2000)]. Although all observed peaks could be indexed to the rhombohedral 2:17 phase (R-3m) many lines were strongly reduced in intensity. Subsequently, the same phenomenon was seen in neutron diffraction patterns from Nd2-xDysFe17-ySiy alloys and conventional refinement using the rhombohedral phase left significant residuals. Fourier mapping revealed additional density along the c-axis chains of Fe dumbbells and rare earth atoms. The perfect a-b-c stacking of the CaCu5 layers with regular 1/3 replacement of the rare earth atoms by Fe dumbbells appears to be broken. Detailed analysis shows that excess Fe dumbbells are incorporated into the structure and some reverse substitution is seen. In addition, the weak intensities are associated with a near equivalence of the 9d and 18h Fe sites, as in the parent CaCu5 phase. The relationship of this new structure to the other CaCu5 derived phases is described. The high Fe concentration creates the possibility of high TC and higher remanence than in the ordered 2:17 compounds.
W. B. Yelon et al., "Observation of Novel Disordered Rhombohedral R₂Fe₁₇ (R=Rare Earth) Based Compounds," Journal of Applied Physics, vol. 91, no. 10, pp. 8486-8488, American Institute of Physics (AIP), May 2002.
The definitive version is available at https://doi.org/10.1063/1.1453325
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© 2002 American Institute of Physics (AIP), All rights reserved.
15 May 2002