Soft X-ray ptychographic reconstructions of a neodymium nickel oxide thin film

Abstract

Rare earth (R) perovskite nickelates RNiO 3 have a rich phase diagram which includes a metal-insulator and paramagnetic-antiferromagnetic phase transition. In neodymium nickel oxide (NdNiO 3 ), these phase transitions coincide, creating a mixedphase state at the critical point. Imaging these competing phases on a nanometerscale may offer unique insights to the driving mechanism behind the metal-insulator transition, which is not well understood. A combination of soft X-ray ptychography and resonant soft X-ray scattering techniques enable direct imaging of the antiferromagnetic domains of NdNiO 3 at the phase transition. In this thesis, I will present ptychographic reconstructions of an epitaxial NdNiO 3 sample near the critical temperature using data taken at the Coherent Soft X-ray Scattering beamline of the National Synchrotron Light Source II. I used phase retrieval algorithms to reconstruct an image of the sample using the custom-developed software package CDTools, which I helped design and build. My reconstructions reveal the antiferromagnetic domains of NdNiO 3 near the critical point, paving the way for future reconstructions of quantum materials. I address several factors limiting the quality of the reconstructions, including uncertainties in the location of the nanopositioners and the beam energy.