Magnetic order in the pyrochlore iridates A ₂Ir ₂O ₇ (A = Y, Yb)

We present results from muon spin relaxation/rotation, magnetization, neutron scattering, and transport measurements on polycrystalline samples of the pyrochlore iridates Y ₂Ir ₂O ₇ (Y-227) and Yb ₂Ir ₂O ₇ (Yb-227). Well-defined spontaneous oscillations of the muon asymmetry are observed together with hysteretic behavior in magnetization below 130 K in Yb-227, indicative of commensurate long-range magnetic order. Similar oscillations are observed in Y-227 below 150 K; however, the onset of hysteretic magnetization at T = 190 K indicates a transition to an intermediate state lacking long-range order as observed in Nd-227. Our results also show that insulating members of the iridate family have nearly identical magnetic ground states, and that the presence of magnetic A-site species does not play any significant role in altering the ground-state properties.