Resistivity Anisotropy and Epitaxial Strain of Rare-Earth Nickelates on STO using Pulsed Laser Deposition*

We report x-ray diffraction, electrical resistivity, and atomic force microscopy measurements on uniform thin-film and half-thin-and-half-thick film NdNiO₃ specimens to probe the effect of varying film thickness on transport properties. In particular, we exploit the strain-induced conductivity of epitaxial ultrathin films of NdNiO₃ as a means to make contact to the bottom of a thicker film, and thus access anisotropic resistivity measurements. We shadow-mask to create a single sample with thinner and thicker portions, enabling electrical contact to both conducting and insulating phases. These devices are also intended for antiferromagnetic spin tunneling measurements in a similar fashion to a magnetic tunnel junction. The samples are prepared by annealing SrTiO₃ (STO) substrates (950°C for ~2 hours) and depositing NdNiO₃ at 650°C using pulsed laser deposition (PLD) with a KrF excimer laser (λ = 245 nm, pulse duration = 25 ns) and a phase-mixed but stoichiometric target. To optimize oxygen content, a partial pressure of O₂ (about 150 mTorr) is introduced to the PLD chamber during deposition.