  The magnetic susceptibility of the 1/1 approximants to icosahedral
quasicrystals in a series of Cd85-xMgxTb15 (x = 5, 10, 15, 20) alloys was
investigated in detail. The occurrence of antiferromagnetic to spin-glass-like
transition was noticed by increasing Mg. Transmission electron microscopy
analysis evidenced a correlation between the magnetic transition and
suppression of the monoclinic superlattice ordering with respect to the
orientation of the Cd4 tetrahedron at T > 100 K. The possible origins of this
phenomenon were discussed in detail. The occurrence of the antiferromagnetic to
spin-glass -like magnetic transition is associated with the combination of
chemical disorder due to a randomized substitution of Cd with Mg and the
orientational disorder of the Cd4 tetrahedra.
