Evidence for Long Range Magnetic Ordering in Perovskite Calcium Iridate Thin Films

The 5d transition metal oxides are promising materials for studying the interplay between electron-electron interactions and strong-spin orbit coupling, which can lead to topological states and other emergent phenomena. Within this class of materials, the semimetal CaIrO₃ (CIO) is of particular interest because it has strong spin-orbit coupling, is predicted to have Dirac electrons, and has exhibited mobility values up to 60,000 cm²/Vs in the bulk. We have synthesized high quality CIO films 2-40nm thick on (001)-oriented LSAT substrates and report on their electronic and magnetic properties. Our CIO films exhibit semi-metallic resistivity and electron-dominated conduction at room temperature, but the majority carrier switches to hole-type at approximately 190K, indicated by a sign change of the Hall coefficient. Hole-dominated conduction persists down to 2K, but at low temperatures the Hall resistance becomes non-linear as a function of field, thus suggesting an additional contribution. Using SQUID magnetometry, we observe a hysteretic magnetization as a function of applied field that is consistent with an anomalous Hall effect and may be attributed to ferromagnetic or canted antiferromagnetic order. Additionally, angular magnetoresistance (MR) measurements indicate an anisotropy in MR when the magnetic field is rotated through the plane of the current, in plane with the current, and about the axis of the current. This anisotropic MR suggests the presence of long range magnetic ordering in our CaIrO₃ thin films.