Half-metallic ferromagnetism and metal-insulator transition in Sn-doped SrRuO3 perovskite oxides

We investigate the electronic and magnetic properties of SrRu1-xSnxO3 by carrying out density-functional-theory calculations to show that a half-metallic ferromagnetic ground state emerges for the Sn doping of x≳0.5. To examine the effect of on-site Coulomb interactions for the Ru d orbitals, which was suggested to enhance the half-metallicity in SrRuO3, we employed both the local spin-density approximation (LSDA) as well as the LSDA + U method. For all the possible configurations of Sn doping for x=1/8,1/4,1/2,5/8,3/4, and 7/8 within the 2×2×2 unit cell, we monitor the Ru t2g bandwidth as well as the valence band maximum in the majority-spin channel and demonstrate that the Ru d electron hopping is blocked by the Sn-substituted sites so that the Ru t2g bandwidth becomes reduced as the doping x increases. For x<0.5, the valence band maximum still touches the Fermi level so that SrRu1-xSnxO3 remains as a usual ferromagnetic metal. A further reduction of the Ru t2g bandwidth for the range of 0.5≲x≲0.7 turns it into a half-metallic ferromagnet. As for x>0.7, the Ru t2g bandwidth gets so narrow that even a small on-site Coulomb interaction, e.g., Ueff=1.0 eV induces a band-gap, which indeed corresponds to a gap of the Ru impurity bands in the SrSnO3 oxide semiconductor.