Electrical and magnetic properties of R₂Mo₂O₇ (R = Nd, Sm, Gd and Dy)

We have made detailed studies of pyrochlore compounds, R₂Mo₂O₇ with R = Nd,Sm,Gd, and Dy. For R = Nd and Sm, we found that apart from the ferromagnetic transition of Mo moments there is another transition of a reentrant spin glass type at lower temperatures, where both the magnetization and heat capacity data show anomalous features. We also observed that the AC susceptibility data are clearly frequency-dependent even in the ferromagnetic phase. In our pressure-dependent magnetization studies, the magnetization data of (Gd_1-xDy_x)₂Mo₂O₇ for x = 0,0.1,0.2, and 0.4 are found to decrease continuously with pressures and, simultaneously, the ferromagnetic transition temperatures move towards lower temperatures. Eventually the ferromagnetic state of (Gd,Dy)₂Mo₂O₇ becomes unstable at higher pressures, and gives way to a spin glass phase that is found to exist at lower temperatures.