Frustrated rare earth magnetism: Spin glasses, spin liquids and spin ices in pyrochlore oxides

Abstract

Rare earth-based materials have played a central role in recent efforts to understand the very unconventional behavior of geometrically frustrated magnetic materials. In particular, rare earth transition metal oxides with the pyrochlore and related structures have been investigated extensively. In the pyrochlore structure both the rare earth and the transition metal sublattices have a topology consisting of corner-sharing tetrahedra and are, thus, geometrically frustrated. Here, we will review progress over the past several years concerning the rare earth titanates, R 2Ti 2O 7, which show a remarkable sensitivity to the electronic structure, specifically, the crystal field ground state of the R 3+ ion. For example, the materials Gd 2Ti 2O 7, Tb 2Ti 2O 7, Dy 2Ti 2O 7 and Ho 2Ti 2O 7 exhibit a wide variety of ground states including unconventional long range order (Gd), a spin liquid state (Tb), and spin ice states (Dy, Ho). Er 2Ti 2O 7 shows long range order but perhaps by the “order by disorder” mechanism and the Yb 2Ti 2O 7 ground state may also be spin liquid like but is presently controversial.