Observation of Novel Disordered Rhombohedral R₂Fe₁₇ (R=rare Earth) Based Compounds


A recent study of (SmGd)Fe 14Si 3 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 Nd 2-xDy xFe 17-ySi y 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 CaCu 5 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 CaCu 5 phase. The relationship of this new structure to the other CaCu 5 derived phases is described. The high Fe concentration creates the possibility of high T C and higher remanence than in the ordered 2:17 compounds. © 2002 American Institute of Physics.



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© 2002 American Institute of Physics (AIP), All rights reserved.