The rare-earth A2Ir2O7 pyrochlore iridates (A = Y, Pr-Lu) constitute a family of materials revealing a plethora of novel and exotic properties. The geometrically frustrated pyrochlore lattice hosts Ir4+ ions displaying strong spin-orbit coupling comparable to electron correlations. In combination with crystal field effects and important f-d exchange between the rare-earth and iridium sites, various magnetic and topological phases emerge. Among others, the topological phases include the topological Mott insulator [1], axion insulator [2] or Weyl semimetal [2,3] and the magnetic phases include the fragmented spin ice state with monopole-like excitations [4] and spin liquid states [5, 6].
The following work is focussed on the magnetic and structural properties of the A = Nd single crystal analogue. In contrast to previous works, e.g. [7], where Nd2Ir2O7 adopts the pyrochlore structure, the present single crystals display a different, unusual crystal structure, attributed to a new Pb-based synthesis method. Magnetic properties, including two magnetic transitions at 41 K and 8 K, demonstrate notable similarities for the two crystal structures. The non-pyrochlore structure found using X-ray diffraction is analysed and compared to the pyrochlore structure, with a focus on the Ir pyrochlore-type tetrahedral sublattice with octahedral O2- crystal fields found in both crystal lattices. The full crystal structure contains two Ir sublattices, three Nd sublattices and one Pb sublattice with a high degree of disorder in the form of vacancies. The magnetic structure, fundamentally tied to the tetrahedral lattice in the pyrochlore case, is examined in the non-pyrochlore samples employing neutron diffraction.