Magnetic and electrical properties of R2Mo2O7 pyrochlore compounds

A combination of ac susceptibility, dc magnetization in a variety of applied fields, and electrical resistivity data is reported for five members of the R2Mo2O7 series of cubic pyrochlore structure oxides, R = Nd, Sm, Gd, Tb, and Y. These measurements extend published studies on the compounds and aid in the clarification and interpretation of the magnetic and electrical transport properties. The metallic ferromagnetics, R = Nd, Sm, and Gd, order at 96, 80, and 57 K, respectively. For R = Nd and Sm this is due most likely to ordering of Mo(IV) moments of about 1 μB. Near 30 K both compounds show hysteresis in the dc magnetization due to complex RMo coupling which give rise to resistivity minimum. For Gd2Mo2O7 there is no low temperature hysteresis, indicating that both sublattices order ferromagnetically at the same temperature. A magnetization anomaly in semiconducting Tb2Mo2O7 at 25 K which is attributed to long range or short range magnetic order is reported for the first time and ac susceptibility data confirm a spin-glass like transition in Y2Mo2O7 reported previously. A correlation between the cubic lattice constant and the electrical and magnetic properties is noted.