Nobuyuki Taira

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.

Magnetic properties of ruthenium pyrochlores R2Ru2O7 (R = rare earth)

Magnetic susceptibility and magnetic hysteresis measurements were performed for rare earth pyrochlores R2Ru2O7 (R = Pr, Nd and Sm-Yb). The compounds of R = Pr, Nd, Sm and Eu show magnetic transitions at 165, 150, 135 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 has been observed. These results show that below the transition temperatures, the magnetic state of these pyrochlores transforms to a spin-glass state. When the temperature is further decreased through ~20 K, apparent cusps have been observed for R = Nd, Sm and Eu in the susceptibility-temperature curves. Magnetic hysteresis measurements at 5.0 K indicate that there is a possibility of a contribution of weak ferromagnetism to the magnetic behaviour of Sm2Ru2O7 at very low temperatures. That is, at these very low temperatures, both the spin-glass state and a weak ferromagnetic state may coexist for Sm2Ru2O7.

Magnetic susceptibility and specific heat studies on heavy rare earth ruthenate pyrochlores R2Ru2O7(R = Gd–Yb)

Magnetic susceptibility and specific heat measurements were performed for heavy rare earth ruthenate pyrochlores R2Ru2O7 (R = Gd, Tb, Dy, Ho, Er, Tm, and Yb). The compounds of R = Tb, Er, and Yb show magnetic transitions at 3.4, 5.4, and 6.3 K, respectively, in the magnetic susceptibility vs. temperature curves. λ-Type anomalies indicating long-range magnetic ordering are observed in the specific heat vs. temperature curves for all of the compounds. At very low temperatures, the presence of short-range magnetic interactions between the rare earth ions for R = Tb, Er, and Yb compounds is indicated from both the susceptibility and the specific heat data.