Invited: Local and Average Crystallographic and Magnetic Structures in Compositionally Complex Oxides

High configurational disorder in compositionally complex oxides (CCOs) can be leveraged to synthesize unique functional properties by extending the rich composition-structure-property phase space of complex oxides. Previous work on CCOs has shown the formation of mixed phase magnetic structures and the ability to tune the magnetic properties, i.e. ordering temperature and average exchange interaction. In our studies, we investigated the effect of compositional disorder on the local and average magnetic and crystallographic structures and magnetic interactions of CCOs. First, by alloying the Y-site of the cuprate superconductor YBa₂Cu₃O_7-x, we showed that the spin and size degrees of freedom can be decoupled, and that high-temperature superconductivity survives disorder on the Y-site with an almost unperturbed order parameter. Second, to better understand the independent tuning knobs of spin and size variance, we studied the magnetic perovskites AMnO₃ and AFeO_3, where the average of the A-site alloying ions’ unpaired spins and ionic sizes was chosen to be that of a known ion, Nd³⁺, allowing for comparison of property changes with the corresponding NdBO₃ undisordered parents. Using bulk magnetometry, synchrotron X-ray diffraction, temperature-dependent neutron diffraction, and pair-distribution function analysis of neutron total scattering we elucidate the subtle differences between the undisordered parent compounds and the CCOs. In addition, the magnetic interaction energies of the ABO₃ CCOs were estimated using an emerging approach based on diffuse elastic neutron powder scattering. Together these studies provide an initial picture of the interplay between different types of compositional complexity and the resulting structure-property changes that can help guide rational design of spin-structures and magnetic behavior in CCOs.