First-principle study of the electronic structure and magnetism in RuSr 2 GdCu 2 O 8 under pressure

We have performed a first-principle calculation of the structural, electronic and high pressure properties of RuSr 2 GdCu 2 O 8 , a ferromagnetic superconductor, by employing a full-potential linearized augmented plane-wave method within the density-functional theory. The effect of pressure was achieved by varying the volume of the unit cell with constant a:b:c ratio. The experimentally observed anti-phase rotation of RuO 6 octahedra has been attributed to the residual forces on O Ru which results in shear strain in the RuO 2 layer. Partial charge analysis shows that applying pressure up to 6 GPa leads to hole creation in the CuO 2 sheets which causes increase in the superconducting transition temperature. We have estimated the Curie temperature T M of this compound in the mean-field approximation using Heisenberg model with first-nearest neighbor exchange interactions determined from DFT calculations for parallel and anti-parallel spin configurations of Ru moment in RuO 2 planes. The effect of pressure causes the magnetic moment of Ru atoms to decrease due to the increase of hybridization between the adjacent Ru atoms. The calculated exchange splitting in Cu d x 2 - y 2 states increases slightly with pressure but it is still very small that it does not affect superconductivity, and the hole doping mechanism is dominant. Copyright EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg 2010