Specific heat and ac susceptibility measurements were performed for R2Ru2O7
(R = Y, Pr, Nd, Sm, Eu, and Lu). For Y2Ru2O7 and Lu2Ru2O7, a lambda-type s
pecific heat anomaly has been observed at 77 and 78 K, respectively, which
is consistent with the magnetic transition found in their magnetic suscepti
bility vs temperature curves. In the real part of the ac susceptibilities,
small cusps are observed at 78 K for Y2Ru2O7 and at 80 K for Lu2Ru2O7. Both
the real part and the imaginary part of the ac susceptibilities are indepe
ndent of frequency, indicating that these compounds are not in the ordinary
spin-glass, Similar large jumps of specific heat are observed at 162, 143,
124, and 118 K for R2Ru2O7 (R = Pr, Nd, Sm, and Eu), For Sm2Ru2O7 and Eu2R
u2O7, no specific heat anomaly has been found at lower temperatures, althou
gh magnetic anomaly was observed at ca. 20 K in their de susceptibility vs
temperature curves, ac susceptibility measurements show that both the real
and the imaginary susceptibilities show anomaly at ca, 20 K and this temper
ature decreases with decreasing frequency. These results strongly indicate
that the transition observed at ca. 20 K is the spin-glass one. The experim
ental results on Nd2Ru2O7 show that magnetic properties of this compound ar
e complicated. (C) 2000 Academic Press.