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

Abstract Ab-initio local-spin density calculations of the structural and magnetic properties of mixed La 1− x Ca x MnO 3 perovskites showing colossal magnetoresistance are reported. For LaMnO 3 our calculations predict an orthorhombic (Pnma) distortion of the crystal, a layered-type antiferromagnetic order and a narrow insulating gap ( E g =162 meV). CaMnO 3 is predicted to be nearly cubic, insulating ( E g =452 meV) and shows rock-salt type antiferromagnetism. Substitution of La by Ca leads to a gradual reduction of the geometrical distortion. At a 50/50 ratio of Ca and La, the groundstate is collinear layered antiferromagnetic and metallic. In disordered alloys with x ∼0.25 or x ∼0.75 the substitutional disorder leads to a weakly noncollinear groundstate, the canting of the Mn-moments being larger in the La-rich regime.