Abstract
Recent developments in the field of superconductivity place nickelates at the forefront of the materials studied in condensed matter physics. The discovery of superconductivity under doping, pressure, and in thin films in multiple families of nickelates renewed the interest into their electronic and magnetic properties.[1-3] Here we perform an investigation of Ni-K edge x-ray absorption and Kβ x-ray emission spectroscopy in thin films of NdNiO3 as a function of temperature and doping. NdNiO3 is a benchmark quantum material displaying a metal-to-insulator transition concomitant with the appearance of magnetic ordering tunable under oxygen treatment.[4] Electronically the resistivity of NdNiO3 raises significantly with the concomitant with the suppression of the magnetic order. The oxygen treatment acts as doping changing the oxidation state of nickel. Our study reveals the effective change of the nickel oxidation state from Ni3+ to Ni2+ and the concomitant change of spin state upon doping proving that oxygen annealing electron doped the system at the nickel site.[5] From the temperature dependence study, we observe little change between 10 K and 300 K indicating that the local electronic effects on nickel and magnetic ordering act at lower energies compared to any spin state transitions. Overall, our work proves the feasibility of XAS and XES hard x-ray experiments on thin films and shows their effectiveness to map the electronic and magnetic structure of nickel oxides.
