Berry curvature induced spontaneous and topological Hall effect in magnetic Weyl semimetallic Nd₂Ir₂O₇ (111) epitaxial thin film

We have performed a temperature and magnetic field dependent magnetotransport study on ~60 nm thick Nd₂Ir₂O₇ (111) epitaxial thin film. Temperature-dependent resistivity shows a semimetallic ground state and observed negligible domain wall conductance in contrast to the bulk sample. Magnetoresistance measurements with the applied magnetic field along (111) direction shows hysteresis, occurs due to plastic deformation of Ir⁴⁺ 5d domains distribution via the change in spin structure of Nd³⁺ 4f moments. Hysteresis in MR vanishes above Nd³⁺ ordering temperature 15 K, suggests f-d exchange interaction between Ir⁴⁺ 5d and Nd³⁺ 4f moments plays a significant role in Ir⁴⁺ domain switching. On the other hand, application of magnetic field along (011) or (001) directions could not modify Ir⁴⁺ domain distribution and does not cause any hysteresis in MR. The presence of hysteresis in MR for the applied field along (111) direction and absence for the field along (011) and (001) directions imply subtle interplay between AFM exchange energy and the field-induced Zeeman energy for those particular field directions. In addition to the nontrivial MR phenomena, the measured Hall resistivity (ρ_xy) shows presence of spontaneous as well as topological Hall components. Observation of large (~75 mΩcm, at 2 K) spontaneous Hall component indirectly confirms presence of Weyl nodes in the electronic band structure of Nd₂Ir₂O₇. A large topological Hall effect also arises due to the noncoplanar spin structure of the Ir⁴⁺ moments.