Variance induced decoupling of spin, lattice, and charge ordering in perovskite nickelates

Perovskite nickelates possess an intimate connection among the structural, electronic, and magnetic orders. We investigate how crystal-field disorder induced by cation size variance impacts the emergence of macroscopic magnetic, structural, and electronic behaviors in single crystal high-entropy oxide nickelate films. The degree of variation in cation sizes hosted on the lattice is found to strongly influence critical ordering temperatures. Resonant x-ray scattering and density functional theory describe how high-variance systems produce local lattice distortions that can be used to manipulate charge disproportionation. The disorder induced shifts to local structure are shown to function as a critical order parameter capable of decoupling the nickelates' distinctive magnetic ground state and metal-insulator transition from its charge ordered state, making it possible to stabilize room-temperature ordered phases not observed in low-variance ternary compounds.