Magnetic properties of the Gd$_2$V$_{0.67}$Mo$_{1.33}$O$_7$ and Y$_2$VMoO$_7$ pyrochlore compounds

It is demonstrated that 50% substitution of vanadium for molybdenum in the pyrochlore lattice of the complex oxide Y$_2$(V$_x$Mo$_{1-x}$)$_2$O$_7$ results in a transition from the spin-glass ground state (at $x$ = 0) to the ferromagnetic state in Y$_2$VMoO$_7$ ($a$ = 10.1645(2) $\mathring{\mathrm{A}}$, $T_\mathrm{C}$ = 55 K). The Gd$_2$V$_{0.67}$Mo$_{1.33}$O$_7$ compound ($a$ = 10.2862(3) $\mathring{\mathrm{A}}$) is a ferromagnet with $T_\mathrm{C}$ (84 K) exceeding that of undoped Gd$_2$MnO$_2$O$_7$.