First Reconstruction of the Antiferromagnetic Order Parameter in NdNiO3 from Resonant Soft X-ray Bragg Ptychography.

Cubic perovskite nickelates with a rare earth ion (ANiO3) exhibit both a metal to insulator transition and a transition to antiferromagnetic order, which coincide in the case of NdNiO3. The many-body nature of these oxides and the interplay between antiferromagnetic order and charge disproportionation leads to a complex landscape involving significant inhomogeneity at the nanoscale. This is exhibited in the form of phase segregation near both the antiferromagnetic and metal to insulator transitions [1]. We report on a first step towards fully characterizing that nanoscale texture using resonant soft x-ray coherent Bragg ptychography at the CSX beamline of NSLS-II. In addition, our work demonstrates for the first time the feasibility of Bragg ptychography in the soft x-ray regime using the weak resonant scattering signals associated with electronic ordering wavevectors.