Charge and spin orders through cascading charge disproportionation transitions in SmBaFe2O6

The recently synthesised A-cation layered double perovskite SmBaFe2O6 containing mixed and unusually high valent Fe3.5+ has been found to show a cascade of charge disproportionation transitions that can be described as 2Fe3.5+ → Fe3+ + Fe4+ → 1.5Fe3+ + 0.5Fe5+ on cooling. While the first charge transition is accompanied by structural and magnetic transitions, the second transition occurs gradually with successive magnetic anomalies and significant temperature and magnetic field hysteresis. To reveal the charge orders and magnetic structures, we propose temperature-dependent neutron diffraction experiments at the WISH diffractometer. The expected results will provide new insights into unusual phase transition phenomena of transition-metal oxides with strong correlation of charge, spin, and lattice degrees of freedom.