Abstract
Structural parameters are systematically investigated for Mo pyrochlore R2Mo2O7 (R = Dy, Gd, Sm, and Nd) by means of synchrotron radiation x-ray powder diffraction. This system shows a crossover from the spin-glass (SG) state to the ferromagnetic metallic (FM) state as the averaged ionic radius r(R) of the rare-earth ion increases. We have found the Mo-O-Mo bond angle increases with r(R) from 129.7 degrees for Dy2Mo2O7 (SG) to 131.5 degrees for Nd2Mo2O7 (FM). This behavior is opposite to the so-called Kanamori-Goodenough rule.