Magnetism behaves very strangely in compounds of lanthanum, strontium, cobalt and oxygen, and researchers have just attained new insight into the decades-old question of why. Pure LaCoO3 is a non-magnetic, narrow-gap semiconductor at low temperatures, but it acquires magnetic properties as the temperature is raised – in contrast with most materials, which tend to lose magnetism at higher temperatures. With strontium doping the magnetic properties become more prominent until, at 18% Sr, the compound becomes metallic and ferromagnetic, like iron. This behavior has often been explained hypothetically by narrow electronic states associated with the d-electrons of cobalt; however, a new study shows that the oxygen becomes partially magnetic, too. X-ray absorption measurements performed at DOE's Advanced Photon Source agree quantitatively with non-localized electronic structure calculations, which showed how the bonding between the oxygen p-orbitals and cobalt d-orbitals formed broad bands of electronic states. The calculated magnetic properties also matched the experiments. This new understanding may help the further development of these materials for applications in high temperature fuel cells and as catalysts for oxygen separation cells for batteries.
Evolution of Magnetic Oxygen States in Sr-Doped LaCoO3