Magnetometry and transport studies of single-crystal pyrochlore iridates*

Magnetic pyrochlore oxides have attracted significant interest due to their geometrically frustrated lattice, which acts to suppress long range magnetic order and leads to a variety of unusual magnetic ground states and exotic excitations.

Some of the most studied pyrochlores are the spin ices Ho₂Ti₂O₇ and Dy₂Ti₂O₇ – here the rare earth ions are ferromagnetic whilst the Ti is nonmagnetic. Recently, the pyrochlore iridates (R₂Ir₂O₇, R = rare earth) have risen to prominence. Here, both the rare earth and the Ir are magnetic; the added complexity afforded by the Ir magnetism may be expected to yield a rich variety of physical phenomena. For instance, most of the pyrochlore iridates exhibit a metal to insulator transition which accompanies the ordering of the Ir into an ‘all-in-all-out’ configuration.

Here we report on magnetisation and resistivity measurements on new single crystals of pyrochlore iridates. We present a systematic study of the evolution of these properties with magnetic field, temperature and angle. Supported by Monte Carlo simulations we present our interpretation of the highly anisotropic and hysteretic behaviour observed as well as its wider significance.