Ca2MnRuO6: Magnetic Order Arising from Chemical Chaos

We predict the existence of half metallicity and thus highly spin-polarized conduction in the completely disordered double-perovskite Ca2MnRuO6, based on first principles calculations. For ordered structures we find the predominantly Ru t2g electrons to be itinerant whereas the Mn eg spins are nearly localized, thus favoring a ferrimagnetic alignment of the Ru and Mn spins. For disordered structures, we find the Mn ions to favor ferromagnetic coupling to other Mn ions in both Mn and Ru sublattices. This explains the overall ferrimagnetic alignment of Mn and Ru ions, irrespective of chemical disorder, that has been found experimentally. The existence of ferrimagnetism and half metallicity in the presence of high levels of chemical disorder is an unexpected combination not seen in other double perovskites.