  Neutron scattering, specific heat and magnetisation measurements on both
powders and single crystals reveal that Dy$_2$Ir$_2$O$_7$ realizes the
fragmented monopole crystal state in which antiferromagnetic order and a
Coulomb phase spin liquid co-inhabit. The measured residual entropy is that of
a hard core dimer liquid, as predicted. Inclusion of Coulomb interactions
allows for a quantitative description of both the thermodynamic data and the
magnetisation dynamics, with the energy scale given by deconfined defects in
the emergent ionic crystal. Our data reveal low energy excitations, as well as
a large distribution of energy barriers down to low temperatures, while the
magnetic response to an applied field suggests that domain wall pinning is
important; results that call for further theoretical modelling.
