Chemical pressure control of exchange interaction in Mo pyrochlore

Abstract

Structural parameters are systematically investigated for Mo pyrochlore ${R}_{2}{\mathrm{Mo}}_{2}{\mathrm{O}}_{7}$ $(R=\mathrm{Dy},$ 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 ${r}_{\mathrm{R}}$ of the rare-earth ion increases. We have found the Mo-O-Mo bond angle increases with ${r}_{\mathrm{R}}$ from $129.7\ifmmode^\circ\else\textdegree\fi{}$ for ${\mathrm{Dy}}_{2}{\mathrm{Mo}}_{2}{\mathrm{O}}_{7}$ (SG) to $131.5\ifmmode^\circ\else\textdegree\fi{}$ for ${\mathrm{Nd}}_{2}{\mathrm{Mo}}_{2}{\mathrm{O}}_{7}$ (FM). This behavior is opposite to the so-called Kanamori-Goodenough rule.