Magnetic properties of iridium pyrochlores R2Ir2O7 (R = Y, Sm, Eu and Lu)

Magnetic susceptibility, magnetic hysteresis, Mossbauer effect, and specific heat measurements were performed for R2Ir2O7 (R = Y, Sm, Eu and Lu), which show magnetic transitions at 150, 115, 120 and 120 K, respectively. Below the transition temperatures there is a large difference in the temperature dependence of the magnetization measured under zero-field-cooled conditions (ZFC) and under field-cooled conditions (FC), but no magnetic hysteresis loop has been observed. The magnetic properties of the Ir pyrochlores are similar to those of isostructural Ru pyrochlores. No sharp anomaly is observed in specific heat data for any of these compounds down to 1.8 K. These results suggest that R2Ir2O7 shows spin-glass-like behaviour below the transition temperatures.