  Physically parallel to ferroelectric morphotropic phase boundary, a phase
boundary separating two ferromagnetic phase of different crystallographic
symmetries was found in TbxDy1-xCo2. High-resolution synchrotron XRD has been
carried out to offer experimental evidence for TbxDy1-xCo2. It has been proved
that TbxDy1-xCo2 (0.6<x<0.7) is a morphotropic phase boundary and that the
crystal structures of tetragonal (x<0.6) and rhombohedral (x>0.7) phase is
distorted from a Laves Phase. Here, a first principles calculation provides a
theoretical explanation on the origin of MBP in TbxDy1-xCo2 and is also
provided for the question of why MPB occurs in TbxDy1-xCo2 alloys.
