BiCuxMn7-xO12: Towards the half-metallic limit

The BiCuxMn7-xO12 (BCMO) quadruple perovskite solid solutions exhibit an exceptionally rich phase diagram in temperature and Cu2+ concentration as the structure negotiates competing orbital and charge degrees of freedom, on top of a Bi3+ polar instability. For x = 2.5, BCMO is a half-metal ferrimagnet (Tc = 350 K), where double exchange produces spin-polarized itinerancy. We will study how the system evolves towards this limit from an insulating state distinguished by short range magnetic interactions and a novel re-entrant structural transition (x = 1). We propose a NPD experiment on samples x = 1.5, 2 & 2.5 in which we aim to better understand a) the re-entrant transition, b) observed low temperature magnetic phase transitions and non-monotonic evolution of the magnetic order, and c) the role of orbital, charge and lone pair degrees of freedom in stabilizing the observed states.