Rhombohedral distortion in highly magnetostrictive Laves phase compounds. [Double tetrahedron model; Tb/sub 1 - x/sub X/FE (R = Gd, Y, Dy)]

A model is presented which produced a magnetostrictively driven rhombohedral distortion (lambda/sub 111/) in cubic diamond-like structures. No tetragonal magnetostrictive distortion (lambda/sub 100/) is allowed, which is consistent with the experimental observations, lambda/sub 111/ much greater than lambda/sub 100/. From x-ray and single crystal measurements we find parallel lambda/sub 111//lambda/sub 100/ parallel greater than 600 for DyFe/sub 2/. Rhombohedral distortions (lambda/sub 111/) are examined in the ternary Tb/sub 1 - x/Gd/sub x/Fe/sub 2/, Tb/sub 1 - x/Y/sub x/Fe/sub 2/ and Tb/sub 1 - x/Dy/sub x/Fe/sub 2/ systems by x-ray methods. The single-ion nature of the giant Tb magnetostriction in TbFe/sub 2/ is verified.