Neutron diffraction study of pyrochlore compound R₂Ru₂O₇ (R=Y, Nd) above and below the spin freezing temperature

Neutron Rietveld analyses have been carried out on Y₂Ru₂O₇ and Nd₂Ru₂O₇ to clarify the primary mechanism of the transition at T_G to the spin-glass-like state which is accompanied by the specific heat jump. The results indicate that the lattice system does not seem to participate in the transition and changes of the neutron diffraction data with decreasing temperature through TG can consistently be understood by the ordering of magnetic moments at Ru sites to an almost long range ordered state, even though the low temperature phase is glassy in the macroscopic sense.