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Abstract:
We present the results of high level band structure calculations on the
important layered compounds LaSr2Mn2O7 and La2CaCu2O6; both of which
have the structure of the m = 2 member of the Ruddlesden-Popper phases
and comprise intergrowths of double perovskite slabs with rock-salt
slabs. The cuprate additionally has an ordered oxygen defect. For
further comparison, the band structure of tetragonal La2CuO4 has also
been calculated. The manganite is a material exhibiting giant
magnetoresistance (GMR) effects and the cuprates can be doped to give
superconductors. The calculations have been performed using the
TB-LMTO-ASA programs within the local (spin) density approximation
L(S)DA; for the manganite, spin-polarized calculations result in a
magnetic ground state; calculations on the ferromagnet and two
antiferromagnetic structures are compared. The calculations show up
similarities and differences between the bonding patterns of these two
structurally related compounds that display widely different ground
states when they are doped. The instabilities on or near the Fermi
surface possibly implicated in the stabilization of the different ground
states are, however, quite similar in character.
