Spin dynamics in geometrically frustrated antiferromagnetic pyrochlores

We have studied the spin dynamics of several antiferromagnetic pyrochlore oxides. These magnets are geometrically frustrated and only reach their ground states at temperatures much lower than that expected from mean field theory. Here we present data on the magnetic nature, especially the spin dynamics of Tb₂Ti₂O₇, Gd₂Ti₂O₇ and Y₂Mo₂O₇. In these systems the ground states are found to be very different. Y₂Mo₂O₇ freezes completely into a spin glass-like state, Tb₂Ti₂O₇ is a cooperative paramagnetic and remains dynamic down to 15 mK and Gd₂Ti₂O₇ enters a unique partially ordered state at ∼1 K.