Glassy Statics and Dynamics in the Chemically Ordered Pyrochlore AntiferromagnetY2Mo2O7

Static and dynamic magnetic correlations in the geometrically frustrated pyrochlore antiferromagnet ${\mathrm{Y}}_2$M${\mathrm{o}}_2$ ${\mathrm{O}}_7$ have been studied using neutron scattering. The material is chemically ordered but displays a spin-freezing transition at $T_g\sim 22.5\mathrm{K}$. We show that dynamic short range order develops below room temperature. Upon cooling the two-spin correlation length never exceeds 5 Å, yet the spin fluctuation rate vanishes in proportion to ${T-T}_g$. For $T<\mathrm{}{T}_g$ low energy spin fluctuations are replaced by static antiferromagnetic short range order with a frozen staggered magnetization $|〈\mathbf{S}〉|/S\approx 0.67\left(2\right)$. Locally the frozen spin structure corresponds to four sublattice ordering with zero magnetization.