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The structure, Curie temperature and magnetostriction of PrxDy1-xFe2 (0 less than or equal to x less than or equal to 0.5) and Pr-0.Dy-4(0.6)(Fe1-yMy)(2) (0 less than or equal to y less than or equal to 0.6) alloys (M = Co, Ni) have been investigated using optical microscopy, x-ray diffraction, ac initial susceptibility and standard strain gauge techniques. The matrix of homogenized PrxDy1-xFe2 alloys is a cubic Laves phase (Pr, Dy)Fe-2 with MgCu2-type structure, with a small amount of second phase (Pr, Dy)Fe-3 when x less than or equal to 0.2. The amount of (Pr, Dy)Fe-3 phase increases with the increase of Pr content, and it becomes the main phase when x = 0.4. When x = 0.5, the matrix is found to be the (Pr, Dy)(2)Fe-17 phase coexisting with a small amount of phases (Pr, Dy)Fe-2, (Pr, Dy)Fe-3 and rare-earth rich phases. For Pr-0.Dy-4(0.6)(Fe1-yCoy)(2) alloys, the amount of (Pr, Dy) (Fe, Co)(2) phase increases with increasing Co content and the phase (Pr, Dy) (Fe, Co)(2) becomes the main phase when y = 0.6. However, the substitution of Ni for Fe up to 60 at % Ni in Pr0.4Dy0.6Fe2 alloys does not favor the formation of the cubic Laves phase (Pr, Dy) (Fe, Ni)(2). The lattice constant of PrxDy1-xFe2 alloys decreases with increasing x, whereas the Curie temperature T-c increases. The magnetostriction of PrxDy1-xFe2 alloys at room temperature exhibits a peak at x = 0.3. The lattice constant of Dy0.6Pr0.4(Fe1-yCoy)(2) alloys decreases slowly with increasing y; T-c shows a peak when y = 0.45, and the room temperature magnetostriction becomes negative when x > 0.45. The Curie temperature of Dy0.6Pr0.4(Fe1-yNiy)(2) alloys decreases with the increase of Ni content. The room temperature magnetostriction of Dy0.6Pr0.4(Fe1-yNiy)(2) also becomes negative when x.0.45. (C) 1999 American Institute of Physics. [S0021-8979(99)04805-7].