Glassy statics and dynamics in the chemically ordered pyrochlore anti-ferromagnet Y2Mo2O7

Static and dynamic magnetic correlations in the geometrically frustrated py rochlore antiferromagnet Y2Mo2O7 have been studied using neutron scattering . The material is chemically ordered but displays a spin-freezing transitio n at T-g similar to 22.5 K. We show that dynamic short range order develops below room temperature. Upon cooling the two-spin correlation length never exceeds 5 Angstrom, yet the spin fluctuation rate vanishes in proportion t o T - T-g. For T < T-g law energy spin fluctuations are replaced by static antiferromagnetic short range order with a frozen staggered magnetization \ < S >\/S approximate to 0.67(2). Locally the frozen spin structure correspo nds to four sublattice ordering with zero magnetization.