Nature of spin freezing transition of geometrically frustrated pyrochlore system R 2Ru 2O 7 (R=rare earth elements and Y)

Abstract

At the spin-glass-like transition of yttrium ruthenium pyrochlore system Y 2Ru 2O 7, a significant jump of the specific heat has been found, suggesting the second order-like nature of the transition. It is commonly observed for other pyrochlore systems R 2Ru 2O 7 (R=various rare earth elements RE). For all REs studied here, the transition temperature T G is larger for the larger R-ions, which may be due to the increase of the transfer energies of the 4 d electrons between the neighboring Ru atoms with increasing RE ionic radius. Neutron Rietveld analyses on Y 2Ru 2O 7 and Nd 2Ru 2O 7 have revealed that below T G, the Ru spins are in an almost long-range ordered antiferromagnetic state, though it is magnetically glassy in a macroscopic sense, and that the lattice system does not participate in the transition. It is concluded that the specific heat jump is created by the purely magnetic origin.