Magnetic structure of Tb₂Ir₂O₇ determined by powder neutron diffraction

We report on the determination of the full magnetic structure of Tb2Ir2O7 including the Ir sublattice by means of powder neutron diffraction. Below T-N similar to 125 K, both the Tb and the Ir sublattices order in a so-called all-in/all-out magnetic structure. However, additional magnetic intensity appears below 10 K on the (111) reflection indicating a change in the magnetic structure. We were able to describe the low-temperature magnetic structure with an additional XY component on the Tb sublattices. The moment sizes at 1.5 K amount to 0.55(3) mu(B)/Ir and 5.22(3) mu(B)/Tb. The Tb3+ moments are titled about 6 degrees off from the [111] direction. Moreover, it was found that the Tb moments couple antiferromagnetically with their six nearest-neighboring Ir moments below TN. This is in contrast to the case of Nd2Ir2O7. The Ir4+ moment sizes of Tb2Ir2O7 are larger than that of Nd2Ir2O7 indicating that hybridization effects between the Ir 5d and the O 2p orbitals are smaller in Tb2Ir2O7