Magnetization and Hall effect measurements on the pyrochlore iridate Nd2Ir2O7

We present magnetization and Hall effect measurements on the pyrochlore iridate Nd$_2$Ir$_2$O$_7$. Previous muon spin rotation measurements have shown that the system undergoes an unusual transition at T$_M$ $\sim$ 110 K into a magnetic phase lacking long-range order, followed by a transition at T$_{LRO}$ $\sim$ 6 K into a state with long-range magnetic order. We observe a small remnant magnetization when cycling through zero magnetic field at temperatures below T$_M$. Below T$_{LRO}$ an additional hysteresis effect appears at a higher field B$_c$ = 2.8 T, together with the appearance of non-monotonic and hysteretic Hall resistance with a maximum at B$_c$. The dependence on field sweep direction suggests a non-trivial transition in the magnetically ordered state similar to that of spin-ice systems. This work was supported in part by National Science Foundation Materials World Network grant DMR-0710525 and by NSF CAREER award DMR-1056625.