  The structural, electrical and magnetic properties of the superconducting
ferromagnets, Gd1.4-xDyxCe0.6Sr2RuCu2O10 (x=0-0.6) are systematically
investigated as a function of Dy doping and temperature. These compounds are
characterised by high temperature superconductivity (Tc ranging from 20-40 K
depending upon the Dy content) coexisting with weak ferromagnetism with two
magnetic transitions (TM2 ranging from 95-106 K and TM1 around 120 K). Doping
with Dy gives no significant structural changes except for a minor change in
the c/a ratio. However the superconducting transition temperature is
significantly suppressed and magnetic ordering temperature enhanced on Dy
doping. These effects are described and discussed.
