The effects of the combined substitution of Y and Ga on the crystallographic structure of Nd2-xYxFe17-yGay intermetallic compounds

The effects of the combined substitution of Y and Ga on the crystallographic structure of Nd2-xYxFe17-xGay, compounds with x = 0, 0.5, 1.0, 1.5 and y = 0, 1, 2, 3 have been investigated using X-ray and neutron powder diffractions. Rietveld refinements of the diffraction data indicate that all the samples crystallize in the rhombohedral Th2Zn17-type structure with only small amounts of alpha iron. It is found that the addition of Ga atoms lessens the decreasing rates of the a-axis and unit cell volume V on the Y content but almost does not affect the decreasing rates of the c-axis. However, the substitution of Y has a positive effect on the increasing rates of the a-axis and unit cell volume V on the Ga content but has a very slight effect on the increasing rate of the c-axis. The c/a ratio of Nd2-xYxFe17-yGay as a function of Ga content exhibits a different increase for different Y content owe to the combined effects of Y and Ga on the crystallographic structure. The substitution of Y is found to have little effect on the site occupancy of Ga in Nd2-xYxFe17-xGay. The combined effects of Y and Ga on the bond lengths and ASBL of Nd2-xYxFe17-yGay indicate that more bonds detrimental to ferromagnetic exchange can be modulated into the desirable ferromagnetic exchange distance range through suitable combined substitution, which provides a valuable way to improve the magnetic properties of rare earth-transition intermetallic compounds. (c) 2005 Elsevier B.V. All rights reserved.