Orbital Magnetism and Spin-Orbit Effects in the Electronic Structure of BaIrO3

The electronic structure and magnetism of Ir 5d(5) states in nonmetallic, weakly ferromagnetic BaIrO3 are probed with x-ray absorption techniques. Contrary to expectation, the Ir 5d orbital moment is found to be similar to 1.5 times larger than the spin moment. This unusual, atomiclike nature of the 5d moment is driven by a strong spin-orbit interaction in heavy Ir ions, as confirmed by the nonstatistical large branching ratio at Ir L-2,L-3 absorption edges. As a consequence, orbital interactions cannot be neglected when addressing the nature of magnetic ordering in BaIrO3. The local moment behavior persists even as the metallic-paramagnetic phase boundary is approached with Sr doping or applied pressure.