  Based on density functional calculation with LDA+U method, we propose that
hypothetical Osmium compounds such as CaOs2O4 and SrOs2O4 can be stabilized in
the geometrically frustrated spinel crystal structure. They also show some
exotic electronic and magnetic properties in a reasonable range of on-site
Coulomb correlation U such as ferromagnetism and orbital magnetoelectric effect
characteristic to Axion electrodynamics. Other electronic phases including 3D
Dirac metal and Mott insulator exist and would make perspective 5d spinels
ideal for applications.
