  DyB4 has a two-dimensional Shastry-Sutherland (Sh-S) lattice with strong
Ising character of the Dy ions. Despite the intrinsic frustrations,
surprisingly, it undergoes two successive transitions: a magnetic ordering at
TN = 20K, and a quadrupole ordering at TQ=12.5 K. From high-resolution neutron
and synchrotron X-ray powder diffraction studies, we have obtained full
structural information on this material in all phases, and demonstrate that
structural modifications occurring at quadrupolar transition lead to the
lifting of frustrations inherent in the Sh-S model. Our study thus provides a
complete experimental picture of how the intrinsic frustration of the Sh-S
lattice can be lifted by the coupling to quadrupole moments. We show that two
other factors, i.e. strong spin-orbit coupling and long-range RKKY interaction
in metallic DyB4, play an important role in this behavior.
