Experimental observations of ferroelectricity in double pyrochlore Dy2Ru2O7

Double pyrochlore Dy2Ru2O7 is synthesized and its magnetism and ferroelectricity below the Ru4+ spin ordering temperature (similar to 100 K) are investigated. The ferroelectric transition appears at similar to 18 K, much higher than the Dy3+ spin ordering point at similar to 1.8 K and lower than the Ru4+ spin ordering point at similar to 100 K. The measured electric polarization at similar to 2 K is as big as 145 mu C/m(2) in the polycrystalline samples. It is argued that the ferroelectricity is possibly ascribed to the electric dipole ordering arising from the collective monopole excitations in the Dy3+ tetrahedrons in prior to the Dy3+ spin ordering into spin-ice like state below similar to 1.8 K.