Magnetoelectric Coupling in the Pyrochlore Ruthenate Gd2Ru2O7

We have prepared polycrystalline samples of Gd2Ru2O7, and have measured the dielectric constant, magnetization and magnetostriction in external fields from 0 to 7 T below 15 K. We find that the dielectric constant of Gd2Ru2O7 significantly changes with external fields, and reveal a finite magnetoelectric coupling in this oxide. Using a simple model in which the spins on the Gd ions feel an internal magnetic field of 7 T from the Ru clusters, we have explained magnetization and magnetoelectric effects qualitatively.