Crystal Structure of the Geometrically Frustrated Magnet Gadolinium Titanate

The movie shows one unit cell of the crystal structure of the geometrically frustrated magnet gadolinium titanate [Gd(2)Ti(2)O(7)]. Actually only the Gd site is shown. Each Gd atom has a localized magnetic moment ("spin") attached to it which is created in the 4f electron shell. When cooled below a temperature of T=1K this substance goes into a magnetically ordered state.

The highly unusual thing is that not all spins participate in the ordering but only the green ones. The gray ones are "frustrated" by competing interactions with their neighbors. As a consequence they stay dynamic and don't become static. For the non-expert: at higher temperature, above 1K, the substance is paramagnetic, which means that all spins are dynamic. The non-frustrated green moments arrange in planes (colored) in the static pattern shown. All this is revealed by neutron scattering.

Georg Ehlers

Oak Ridge National Laboratory