Structure and magnetostriction of PrxDy1−xFe2 and Pr0.4Dy0.6(Fe1−yMy)2 alloys (M=Co, Ni)

Abstract

The structure, Curie temperature and magnetostriction of PrxDy1−xFe2 (0⩽x⩽0.5) and Pr0.4Dy0.6(Fe1−yMy)2 (0⩽y⩽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)Fe2 with MgCu2-type structure, with a small amount of second phase (Pr, Dy)Fe3 when x⩽0.2. The amount of (Pr, Dy)Fe3 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)2Fe17 phase coexisting with a small amount of phases (Pr, Dy)Fe2, (Pr, Dy)Fe3 and rare-earth rich phases. For Pr0.4Dy0.6(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 Tc 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; Tc 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 decreses with the increase of Ni content. The room temperature magnetostriction of Dy0.6Pr0.4(Fe1−yNiy)2 also becomes negative when x>0.45.