Epitaxial growth and stoichiometry control of pyrochlore Nd2Ru2O7 thin films

We report on the epitaxial growth of pyrochlore NRO thin films utilizing a reactive off-axis sputtering technique. The growth process employed Ru and Nd metal targets with a repetitive substrate temperature sequence. X-ray diffraction, magnetic susceptibility, and spectroscopic ellipsometry measurements confirm that the structural, magnetic, and electronic properties of near-stoichiometric NRO films match those of the bulk material. Our spin-polarized density functional calculations based on {Nd}₂{Ru}₂{O}₇ structural parameters accurately describe the optical spectra and assign Hubbard bands to the interband transitions observed above the optical band gap of 0.2 eV. By utilizing the technique's capability to adjust the degree of ruthenium deficiency, we investigated {Nd}₂{Ru}₂{O}₇ films across a wide range of stoichiometric variations. Decreasing the Ru/Nd ratio results in lattice expansion, an increase in the optical band gap, and the suppression of Ru 4d intersite optical transitions. Additionally, this adjustment facilitates the elimination of minor inclusions of a ferromagnetic {NdO}_x impurity phase, influencing the magnetic properties of stoichiometric films at low temperatures. The successful growth of {Nd}₂{Ru}₂{O}₇ films opens up promising opportunities for designing and exploring strain- and light-induced states in pyrochlore ruthenates. Published by the American Physical Society 2024