Ab initio local-spin-density study of the structural and magnetic properties of La1-xCaxMnO3 systems

Ab-initio local-spin density calculations of the structural and magnetic pr operties of mixed La1-xCaxMnO3 perovskites showing colossal magnetoresistan ce are reported. For LaMnO3 our calculations predict an orthorhombic (Pnma) distortion of the crystal, a layered-type antiferromagnetic order and a na rrow insulating gap (E-g = 162 meV). CaMnO3 is predicted to be nearly cubic , insulating (E-g = 452 meV) and shows rock-salt type antiferromagnetism. S ubstitution of La by Ca leads to a gradual reduction of the geometrical dis tortion. At a 50/50 ratio of Ca and La, the groundstate is collinear layere d antiferromagnetic and metallic. In disordered alloys with x similar to 0. 25 or x similar to 0.75 the substitutional disorder leads to a weakly nonco llinear groundstate, the canting of the Mn-moments being larger in the La-r ich regime. (C) 2001 Elsevier Science B.V. All rights reserved.